Documents Ganeti version 3.1
Ganeti is a virtualization cluster management software. You are expected to be a system administrator familiar with your Linux distribution and the Xen or KVM virtualization environments before using it.
The various components of Ganeti all have man pages and interactive help. This manual though will help you getting familiar with the system by explaining the most common operations, grouped by related use.
After a terminology glossary and a section on the prerequisites needed to use this manual, the rest of this document is divided in sections for the different targets that a command affects: instance, nodes, etc.
This section provides a small introduction to Ganeti terminology, which might be useful when reading the rest of the document.
A set of machines (nodes) that cooperate to offer a coherent, highly available virtualization service under a single administration domain.
A physical machine which is member of a cluster. Nodes are the basic cluster infrastructure, and they don’t need to be fault tolerant in order to achieve high availability for instances.
Node can be added and removed (if they host no instances) at will from the cluster. In a HA cluster and only with HA instances, the loss of any single node will not cause disk data loss for any instance; of course, a node crash will cause the crash of its primary instances.
A node belonging to a cluster can be in one of the following roles at a given time:
master node, which is the node from which the cluster is controlled
master candidate node, only nodes in this role have the full cluster configuration and knowledge, and only master candidates can become the master node
regular node, which is the state in which most nodes will be on bigger clusters (>20 nodes)
drained node, nodes in this state are functioning normally but the cannot receive new instances; the intention is that nodes in this role have some issue and they are being evacuated for hardware repairs
offline node, in which there is a record in the cluster configuration about the node, but the daemons on the master node will not talk to this node; any instances declared as having an offline node as either primary or secondary will be flagged as an error in the cluster verify operation
Depending on the role, each node will run a set of daemons:
the ganeti-noded daemon, which controls the manipulation of this node’s hardware resources; it runs on all nodes which are in a cluster
the ganeti-confd daemon (Ganeti 2.1+) which runs on all master candidates and answers queries about the cluster configuration.
the ganeti-wconfd daemon (Ganeti 2.12+) which runs on the master node and allows control of the cluster
the ganeti-luxid daemon which runs on the master node and answers queries related to the live state of the cluster, and schedules cluster jobs
the ganeti-rapi daemon which runs on the master node and offers an HTTP-based API for the cluster
the ganeti-kvmd daemon which runs on all KVM-enabled nodes when the cluster parameter user_shutdown is enabled, and determines whether the instance was shutdown by a user or an administrator
the ganeti-mond daemon which runs on all nodes and collects information about the cluster
the ganeti-metad daemon which is started on demand and provides information about the cluster to OS install scripts or instances.
Beside the node role, there are other node flags that influence its behaviour:
the master_capable flag denotes whether the node can ever become a master candidate; setting this to ‘no’ means that auto-promotion will never make this node a master candidate; this flag can be useful for a remote node that only runs local instances, and having it become a master is impractical due to networking or other constraints
the vm_capable flag denotes whether the node can host instances or not; for example, one might use a non-vm_capable node just as a master candidate, for configuration backups; setting this flag to no disallows placement of instances of this node, deactivates hypervisor and related checks on it (e.g. bridge checks, LVM check, etc.), and removes it from cluster capacity computations
A virtual machine which runs on a cluster. It can be a fault tolerant, highly available entity.
An instance has various parameters, which are classified in three
categories: hypervisor related-parameters (called hvparams), general
parameters (called beparams) and per network-card parameters (called
nicparams). All these parameters can be modified either at instance
level or via defaults at cluster level.
The are multiple options for the storage provided to an instance; while the instance sees the same virtual drive in all cases, the node-level configuration varies between them.
There are several disk templates you can choose from:
disklessThe instance has no disks. Only used for special purpose operating systems or for testing.
file *The instance will use plain files as backend for its disks. No redundancy is provided, and this is somewhat more difficult to configure for high performance.
sharedfile *The instance will use plain files as backend, but Ganeti assumes that those files will be available and in sync automatically on all nodes. This allows live migration and failover of instances using this method.
plainThe instance will use LVM devices as backend for its disks. No redundancy is provided.
drbdNote
This is only valid for multi-node clusters using DRBD 8.0+
A mirror is set between the local node and a remote one, which must be specified with the second value of the –node option. Use this option to obtain a highly available instance that can be failed over to a remote node should the primary one fail.
Note
Ganeti does not support DRBD stacked devices: DRBD stacked setup is not fully symmetric and as such it is not working with live migration.
rbdThe instance will use Volumes inside a RADOS cluster as backend for its disks. It will access them using the RADOS block device (RBD).
gluster *The instance will use a Gluster volume for instance storage. Disk
images will be stored in the top-level ganeti/ directory of the
volume. This directory will be created automatically for you.
extThe instance will use an external storage provider. See ganeti-extstorage-interface(7) for how to implement one.
Note
Disk templates marked with an asterisk require Ganeti to access the
file system. Ganeti will refuse to do so unless you whitelist the
relevant paths in the file storage paths configuration which,
with default configure-time paths is located
in /etc/ganeti/file-storage-paths.
The default paths used by Ganeti are:
Disk template |
Default path |
|---|---|
|
|
|
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Those paths can be changed at gnt-cluster init time. See
gnt-cluster(8) for details.
A framework for using external (user-provided) scripts to compute the placement of instances on the cluster nodes. This eliminates the need to manually specify nodes in instance add, instance moves, node evacuate, etc.
In order for Ganeti to be able to use these scripts, they must be place
in the iallocator directory (usually lib/ganeti/iallocators under
the installation prefix, e.g. /usr/local).
An instance has a primary and depending on the disk configuration, might also have a secondary node. The instance always runs on the primary node and only uses its secondary node for disk replication.
Similarly, the term of primary and secondary instances when talking about a node refers to the set of instances having the given node as primary, respectively secondary.
While not directly visible by an end-user, it’s useful to know that a basic cluster operation (e.g. starting an instance) is represented internally by Ganeti as an OpCode (abbreviation from operation code). These OpCodes are executed as part of a Job. The OpCodes in a single Job are processed serially by Ganeti, but different Jobs will be processed (depending on resource availability) in parallel. They will not be executed in the submission order, but depending on resource availability, locks and (starting with Ganeti 2.3) priority. An earlier job may have to wait for a lock while a newer job doesn’t need any locks and can be executed right away. Operations requiring a certain order need to be submitted as a single job, or the client must submit one job at a time and wait for it to finish before continuing.
For example, shutting down the entire cluster can be done by running the
command gnt-instance shutdown --all, which will submit for each
instance a separate job containing the “shutdown instance” OpCode.
You need to have your Ganeti cluster installed and configured before you try any of the commands in this document. Please follow the Ganeti installation tutorial for instructions on how to do that.
The add operation might seem complex due to the many parameters it accepts, but once you have understood the (few) required parameters and the customisation capabilities you will see it is an easy operation.
The add operation requires at minimum five parameters:
the OS for the instance
the disk template
the disk count and size
the node specification or alternatively the iallocator to use
and finally the instance name
The OS for the instance must be visible in the output of the command
gnt-os list and specifies which guest OS to install on the instance.
The disk template specifies what kind of storage to use as backend for the (virtual) disks presented to the instance; note that for instances with multiple virtual disks, they all must be of the same type.
The node(s) on which the instance will run can be given either manually,
via the -n option, or computed automatically by Ganeti, if you have
installed any iallocator script.
With the above parameters in mind, the command is:
$ gnt-instance add \
-n TARGET_NODE:SECONDARY_NODE \
-o OS_TYPE \
-t DISK_TEMPLATE -s DISK_SIZE \
INSTANCE_NAME
The instance name must be resolvable (e.g. exist in DNS) and usually points to an address in the same subnet as the cluster itself.
The above command has the minimum required options; other options you can give include, among others:
The maximum/minimum memory size (-B maxmem, -B minmem)
(-B memory can be used to specify only one size)
The number of virtual CPUs (-B vcpus)
Arguments for the NICs of the instance; by default, a single-NIC
instance is created. The IP and/or bridge of the NIC can be changed
via --net 0:ip=IP,link=BRIDGE
See ganeti-instance(8) for the detailed option list.
For example if you want to create an highly available instance, with a
single disk of 50GB and the default memory size, having primary node
node1 and secondary node node3, use the following command:
$ gnt-instance add -n node1:node3 -o debootstrap -t drbd -s 50G \
instance1
There is a also a command for batch instance creation from a
specification file, see the batch-create operation in the
gnt-instance manual page.
Removing an instance is even easier than creating one. This operation is irreversible and destroys all the contents of your instance. Use with care:
$ gnt-instance remove INSTANCE_NAME
Instances are automatically started at instance creation time. To manually start one which is currently stopped you can run:
$ gnt-instance startup INSTANCE_NAME
Ganeti will start an instance with up to its maximum instance memory. If not enough memory is available Ganeti will use all the available memory down to the instance minimum memory. If not even that amount of memory is free Ganeti will refuse to start the instance.
Note, that this will not work when an instance is in a permanently
stopped state offline. In this case, you will first have to
put it back to online mode by running:
$ gnt-instance modify --online INSTANCE_NAME
The command to stop the running instance is:
$ gnt-instance shutdown INSTANCE_NAME
If you want to shut the instance down more permanently, so that it does not require dynamically allocated resources (memory and vcpus), after shutting down an instance, execute the following:
$ gnt-instance modify --offline INSTANCE_NAME
Warning
Do not use the Xen or KVM commands directly to stop
instances. If you run for example xl shutdown or xl destroy
on an instance Ganeti will automatically restart it (via
the ganeti-watcher(8) command which is launched via cron).
Instances can also be shutdown by the user from within the instance, in which case they will marked accordingly and the ganeti-watcher(8) will not restart them. See gnt-cluster(8) for details.
There are two ways to get information about instances: listing instances, which does a tabular output containing a given set of fields about each instance, and querying detailed information about a set of instances.
The command to see all the instances configured and their status is:
$ gnt-instance list
The command can return a custom set of information when using the -o
option (as always, check the manpage for a detailed specification). Each
instance will be represented on a line, thus making it easy to parse
this output via the usual shell utilities (grep, sed, etc.).
To get more detailed information about an instance, you can run:
$ gnt-instance info INSTANCE
which will give a multi-line block of information about the instance, it’s hardware resources (especially its disks and their redundancy status), etc. This is harder to parse and is more expensive than the list operation, but returns much more detailed information.
Ganeti will always make sure an instance has a value between its maximum and its minimum memory available as runtime memory. As of version 2.6 Ganeti will only choose a size different than the maximum size when starting up, failing over, or migrating an instance on a node with less than the maximum memory available. It won’t resize other instances in order to free up space for an instance.
If you find that you need more memory on a node any instance can be manually resized without downtime, with the command:
$ gnt-instance modify -m SIZE INSTANCE_NAME
The same command can also be used to increase the memory available on an instance, provided that enough free memory is available on its node, and the specified size is not larger than the maximum memory size the instance had when it was first booted (an instance will be unable to see new memory above the maximum that was specified to the hypervisor at its boot time, if it needs to grow further a reboot becomes necessary).
You can create a snapshot of an instance disk and its Ganeti configuration, which then you can backup, or import into another cluster. The way to export an instance is:
$ gnt-backup export -n TARGET_NODE INSTANCE_NAME
The target node can be any node in the cluster with enough space under
/srv/ganeti to hold the instance image. Use the --noshutdown
option to snapshot an instance without rebooting it. Note that Ganeti
only keeps one snapshot for an instance - any previous snapshot of the
same instance existing cluster-wide under /srv/ganeti will be
removed by this operation: if you want to keep them, you need to move
them out of the Ganeti exports directory.
Importing an instance is similar to creating a new one, but additionally one must specify the location of the snapshot. The command is:
$ gnt-backup import -n TARGET_NODE \
--src-node=NODE --src-dir=DIR INSTANCE_NAME
By default, parameters will be read from the export information, but you can of course pass them in via the command line - most of the options available for the command gnt-instance add are supported here too.
There is a possibility to import a foreign instance whose disk data is already stored as LVM volumes without going through copying it: the disk adoption mode.
For this, ensure that the original, non-managed instance is stopped, then create a Ganeti instance in the usual way, except that instead of passing the disk information you specify the current volumes:
$ gnt-instance add -t plain -n HOME_NODE ... \
--disk 0:adopt=lv_name[,vg=vg_name] INSTANCE_NAME
This will take over the given logical volumes, rename them to the Ganeti
standard (UUID-based), and without installing the OS on them start
directly the instance. If you configure the hypervisor similar to the
non-managed configuration that the instance had, the transition should
be seamless for the instance. For more than one disk, just pass another
disk parameter (e.g. --disk 1:adopt=...).
The kernel that instances uses to bootup can come either from the node, or from instances themselves, depending on the setup.
With Xen PVM, there are three options.
First, you can use a kernel from the node, by setting the hypervisor parameters as such:
kernel_path to a valid file on the node (and appropriately
initrd_path)
kernel_args optionally set to a valid Linux setting (e.g. ro)
root_path to a valid setting (e.g. /dev/xvda1)
bootloader_path and bootloader_args to empty
Alternatively, you can delegate the kernel management to instances, and
use either pvgrub or the deprecated pygrub. For this, you must
install the kernels and initrds in the instance and create a valid GRUB
v1 configuration file.
For pvgrub (new in version 2.4.2), you need to set:
kernel_path to point to the pvgrub loader present on the node
(e.g. /usr/lib/xen/boot/pv-grub-x86_32.gz)
kernel_args to the path to the GRUB config file, relative to the
instance (e.g. (hd0,0)/grub/menu.lst)
root_path must be empty
bootloader_path and bootloader_args to empty
While pygrub is deprecated, here is how you can configure it:
bootloader_path to the pygrub binary (e.g. /usr/bin/pygrub)
the other settings are not important
More information can be found in the Xen wiki pages for pvgrub and pygrub.
For KVM also the kernel can be loaded either way.
For loading the kernels from the node, you need to set:
kernel_path to a valid value
initrd_path optionally set if you use an initrd
kernel_args optionally set to a valid value (e.g. ro)
If you want instead to have the instance boot from its disk (and execute
its bootloader), simply set the kernel_path parameter to an empty
string, and all the others will be ignored.
Note
This section only applies to multi-node clusters
There are three ways to exchange an instance’s primary and secondary nodes; the right one to choose depends on how the instance has been created and the status of its current primary node. See Restoring redundancy for DRBD-based instances for information on changing the secondary node. Note that it’s only possible to change the primary node to the secondary and vice-versa; a direct change of the primary node with a third node, while keeping the current secondary is not possible in a single step, only via multiple operations as detailed in Instance relocation.
If an instance is built in highly available mode you can at any time fail it over to its secondary node, even if the primary has somehow failed and it’s not up anymore. Doing it is really easy, on the master node you can just run:
$ gnt-instance failover INSTANCE_NAME
That’s it. After the command completes the secondary node is now the primary, and vice-versa.
The instance will be started with an amount of memory between its
maxmem and its minmem value, depending on the free memory on its
target node, or the operation will fail if that’s not possible. See
Startup/shutdown for details.
If the instance’s disk template is of type rbd, then you can specify the target node (which can be any node) explicitly, or specify an iallocator plugin. If you omit both, the default iallocator will be used to determine the target node:
$ gnt-instance failover -n TARGET_NODE INSTANCE_NAME
If an instance is built in highly available mode, it currently runs and both its nodes are running fine, you can migrate it over to its secondary node, without downtime. On the master node you need to run:
$ gnt-instance migrate INSTANCE_NAME
The current load on the instance and its memory size will influence how long the migration will take. In any case, for both KVM and Xen hypervisors, the migration will be transparent to the instance.
If the destination node has less memory than the instance’s current
runtime memory, but at least the instance’s minimum memory available
Ganeti will automatically reduce the instance runtime memory before
migrating it, unless the --no-runtime-changes option is passed, in
which case the target node should have at least the instance’s current
runtime memory free.
If the instance’s disk template is of type rbd, then you can specify the target node (which can be any node) explicitly, or specify an iallocator plugin. If you omit both, the default iallocator will be used to determine the target node:
$ gnt-instance migrate -n TARGET_NODE INSTANCE_NAME
If an instance has not been create as mirrored, then the only way to change its primary node is to execute the move command:
$ gnt-instance move -n NEW_NODE INSTANCE
This has a few prerequisites:
the instance must be stopped
its current primary node must be on-line and healthy
the disks of the instance must not have any errors
Since this operation actually copies the data from the old node to the new node, expect it to take proportional to the size of the instance’s disks and the speed of both the nodes’ I/O system and their networking.
Disk failures are a common cause of errors in any server deployment. Ganeti offers protection from single-node failure if your instances were created in HA mode, and it also offers ways to restore redundancy after a failure.
It is important to note that for Ganeti to be able to do any disk operation, the Linux machines on top of which Ganeti runs must be consistent; for LVM, this means that the LVM commands must not return failures; it is common that after a complete disk failure, any LVM command aborts with an error similar to:
$ vgs
/dev/sdb1: read failed after 0 of 4096 at 0: Input/output error
/dev/sdb1: read failed after 0 of 4096 at 750153695232: Input/output error
/dev/sdb1: read failed after 0 of 4096 at 0: Input/output error
Couldn't find device with uuid 't30jmN-4Rcf-Fr5e-CURS-pawt-z0jU-m1TgeJ'.
Couldn't find all physical volumes for volume group xenvg.
Before restoring an instance’s disks to healthy status, it’s needed to fix the volume group used by Ganeti so that we can actually create and manage the logical volumes. This is usually done in a multi-step process:
first, if the disk is completely gone and LVM commands exit with “Couldn’t find device with uuid…” then you need to run the command:
$ vgreduce --removemissing VOLUME_GROUP
after the above command, the LVM commands should be executing normally (warnings are normal, but the commands will not fail completely).
if the failed disk is still visible in the output of the pvs
command, you need to deactivate it from allocations by running:
$ pvs -x n /dev/DISK
At this point, the volume group should be consistent and any bad physical volumes should not longer be available for allocation.
Note that since version 2.1 Ganeti provides some commands to automate these two operations, see Generalized storage handling.
A DRBD instance has two nodes, and the storage on one of them has failed. Depending on which node (primary or secondary) has failed, you have three options at hand:
if the storage on the primary node has failed, you need to re-create the disks on it
if the storage on the secondary node has failed, you can either re-create the disks on it or change the secondary and recreate redundancy on the new secondary node
Of course, at any point it’s possible to force re-creation of disks even though everything is already fine.
For all three cases, the replace-disks operation can be used:
# re-create disks on the primary node
$ gnt-instance replace-disks -p INSTANCE_NAME
# re-create disks on the current secondary
$ gnt-instance replace-disks -s INSTANCE_NAME
# change the secondary node, via manual specification
$ gnt-instance replace-disks -n NODE INSTANCE_NAME
# change the secondary node, via an iallocator script
$ gnt-instance replace-disks -I SCRIPT INSTANCE_NAME
# since Ganeti 2.1: automatically fix the primary or secondary node
$ gnt-instance replace-disks -a INSTANCE_NAME
Since the process involves copying all data from the working node to the target node, it will take a while, depending on the instance’s disk size, node I/O system and network speed. But it is (barring any network interruption) completely transparent for the instance.
Added in version 2.1.
For non-redundant instances, there isn’t a copy (except backups) to
re-create the disks. But it’s possible to at-least re-create empty
disks, after which a reinstall can be run, via the recreate-disks
command:
$ gnt-instance recreate-disks INSTANCE
Note that this will fail if the disks already exists. The instance can
be assigned to new nodes automatically by specifying an iallocator
through the --iallocator option.
It is possible to convert between a non-redundant instance of type
plain (LVM storage) and redundant drbd via the gnt-instance
modify command:
# start with a non-redundant instance
$ gnt-instance add -t plain ... INSTANCE
# later convert it to redundant
$ gnt-instance stop INSTANCE
$ gnt-instance modify -t drbd -n NEW_SECONDARY INSTANCE
$ gnt-instance start INSTANCE
# and convert it back
$ gnt-instance stop INSTANCE
$ gnt-instance modify -t plain INSTANCE
$ gnt-instance start INSTANCE
The conversion must be done while the instance is stopped, and converting from plain to drbd template presents a small risk, especially if the instance has multiple disks and/or if one node fails during the conversion procedure). As such, it’s recommended (as always) to make sure that downtime for manual recovery is acceptable and that the instance has up-to-date backups.
From an instance’s primary node you can have access to its disks. Never ever mount the underlying logical volume manually on a fault tolerant instance, or will break replication and your data will be inconsistent. The correct way to access an instance’s disks is to run (on the master node, as usual) the command:
$ gnt-instance activate-disks INSTANCE
And then, on the primary node of the instance, access the device that gets created. For example, you could mount the given disks, then edit files on the filesystem, etc.
Note that with partitioned disks (as opposed to whole-disk filesystems), you will need to use a tool like kpartx(8):
# on node1
$ gnt-instance activate-disks instance1
node3:disk/0:…
$ ssh node3
# on node 3
$ kpartx -l /dev/…
$ kpartx -a /dev/…
$ mount /dev/mapper/… /mnt/
# edit files under mnt as desired
$ umount /mnt/
$ kpartx -d /dev/…
$ exit
# back to node 1
After you’ve finished you can deactivate them with the deactivate-disks command, which works in the same way:
$ gnt-instance deactivate-disks INSTANCE
Note that if any process started by you is still using the disks, the above command will error out, and you must cleanup and ensure that the above command runs successfully before you start the instance, otherwise the instance will suffer corruption.
The command to access a running instance’s console is:
$ gnt-instance console INSTANCE_NAME
Use the console normally and then type ^] when done, to exit.
There is a wrapper command for rebooting instances:
$ gnt-instance reboot instance2
By default, this does the equivalent of shutting down and then starting the instance, but it accepts parameters to perform a soft-reboot (via the hypervisor), a hard reboot (hypervisor shutdown and then startup) or a full one (the default, which also de-configures and then configures again the disks of the instance).
Should you have any problems with instance operating systems the command to see a complete status for all your nodes is:
$ gnt-os diagnose
While it is not possible to move an instance from nodes (A, B) to
nodes (C, D) in a single move, it is possible to do so in a few
steps:
# instance is located on A, B
$ gnt-instance replace-disks -n nodeC instance1
# instance has moved from (A, B) to (A, C)
# we now flip the primary/secondary nodes
$ gnt-instance migrate instance1
# instance lives on (C, A)
# we can then change A to D via:
$ gnt-instance replace-disks -n nodeD instance1
Which brings it into the final configuration of (C, D). Note that we
needed to do two replace-disks operation (two copies of the instance
disks), because we needed to get rid of both the original nodes (A and
B).
Ganeti used to describe NICs of an Instance with an IP, a MAC, a connectivity link and mode. This had three major shortcomings:
there was no easy way to assign a unique IP to an instance
network info (subnet, gateway, domain, etc.) was not available on target node (kvm-ifup, hooks, etc)
one should explicitly pass L2 info (mode, and link) to every NIC
Plus there was no easy way to get the current networking overview (which instances are on the same L2 or L3 network, which IPs are reserved, etc).
All the above required an external management tool that has an overall view and provides the corresponding info to Ganeti.
gnt-network aims to support a big part of this functionality inside Ganeti and abstract the network as a separate entity. Currently, a Ganeti network provides the following:
A single IPv4 pool, subnet and gateway
Connectivity info per nodegroup (mode, link)
MAC prefix for each NIC inside the network
IPv6 prefix/Gateway related to this network
Tags
IP pool management ensures IP uniqueness inside this network. The user can pass ip=pool,network=test and will:
Get the first available IP in the pool
Inherit the connectivity mode and link of the network’s netparams
NIC will obtain the MAC prefix of the network
All network related info will be available as environment variables in kvm-ifup scripts and hooks, so that they can dynamically manage all networking-related setup on the host.
To create a network do:
# gnt-network add --network=192.0.2.0/24 --gateway=192.0.2.1 test
Please see all other available options (–add-reserved-ips, –mac-prefix, –network6, –gateway6, –tags).
Currently, IPv6 info is not used by Ganeti itself. It only gets exported to NIC configuration scripts and hooks via environment variables.
To make this network available on a nodegroup you should specify the connectivity mode and link during connection:
# gnt-network connect --nic-parameters mode=bridged,link=br100 test default nodegroup1
To add a NIC inside this network:
# gnt-instance modify --net -1:add,ip=pool,network=test inst1
This will let a NIC obtain a unique IP inside this network, and inherit the nodegroup’s netparams (bridged, br100). IP here is optional. If missing the NIC will just get the L2 info.
To move an existing NIC from a network to another and remove its IP:
# gnt-instance modify --net -1:ip=none,network=test1 inst1
This will release the old IP from the old IP pool and the NIC will inherit the new nicparams.
On the above actions there is a extra option –no-conflicts-ckeck. This does not check for conflicting setups. Specifically:
When a network is added, IPs of nodes and master are not being checked.
When connecting a network on a nodegroup, IPs of instances inside this nodegroup are not checked whether they reside inside the subnet or not.
When specifying explicitly a IP without passing a network, Ganeti will not check if this IP is included inside any available network on the nodegroup.
All the aforementioned steps assure NIC configuration from the Ganeti perspective. Of course this has nothing to do, how the instance eventually will get the desired connectivity (IPv4, IPv6, default routes, DNS info, etc) and where will the IP resolve. This functionality is managed by the external components.
Let’s assume that the VM will need to obtain a dynamic IP via DHCP, get a SLAAC address, and use DHCPv6 for other configuration information (in case RFC-6106 is not supported by the client, e.g. Windows). This means that the following external services are needed:
A DHCP server
An IPv6 router sending Router Advertisements
A DHCPv6 server exporting DNS info
A dynamic DNS server
These components must be configured dynamically and on a per NIC basis. The way to do this is by using custom kvm-ifup scripts and hooks.
There are much fewer node operations available than for instances, but they are equivalently important for maintaining a healthy cluster.
It is at any time possible to extend the cluster with one more node, by using the node add operation:
$ gnt-node add NEW_NODE
If the cluster has a replication network defined, then you need to pass
the -s REPLICATION_IP parameter to this option.
A variation of this command can be used to re-configure a node if its Ganeti configuration is broken, for example if it has been reinstalled by mistake:
$ gnt-node add --readd EXISTING_NODE
This will reinitialise the node as if it’s been newly added, but while
keeping its existing configuration in the cluster (primary/secondary IP,
etc.), in other words you won’t need to use -s here.
A node can be in different roles, as explained in the Ganeti terminology section. Promoting a node to the master role is special, while the other roles are handled all via a single command.
If you want to promote a different node to the master role (for whatever reason), run on any other master-candidate node the command:
$ gnt-cluster master-failover
and the node you ran it on is now the new master. In case you try to run this on a non master-candidate node, you will get an error telling you which nodes are valid.
The gnt-node modify command can be used to select a new role:
# change to master candidate
$ gnt-node modify -C yes NODE
# change to drained status
$ gnt-node modify -D yes NODE
# change to offline status
$ gnt-node modify -O yes NODE
# change to regular mode (reset all flags)
$ gnt-node modify -O no -D no -C no NODE
Note that the cluster requires that at any point in time, a certain
number of nodes are master candidates, so changing from master candidate
to other roles might fail. It is recommended to either force the
operation (via the --force option) or first change the number of
master candidates in the cluster - see Standard operations.
There are two steps of moving instances off a node:
moving the primary instances (actually converting them into secondary instances)
moving the secondary instances (including any instances converted in the step above)
For this step, you can use either individual instance move commands (as seen in Changing the primary node) or the bulk per-node versions; these are:
$ gnt-node migrate NODE
$ gnt-node evacuate -s NODE
Note that the instance “move” command doesn’t currently have a node equivalent.
Both these commands, or the equivalent per-instance command, will make this node the secondary node for the respective instances, whereas their current secondary node will become primary. Note that it is not possible to change in one step the primary node to another node as primary, while keeping the same secondary node.
For the evacuation of secondary instances, a command called gnt-node evacuate is provided and its syntax is:
$ gnt-node evacuate -I IALLOCATOR_SCRIPT NODE
$ gnt-node evacuate -n DESTINATION_NODE NODE
The first version will compute the new secondary for each instance in turn using the given iallocator script, whereas the second one will simply move all instances to DESTINATION_NODE.
Once a node no longer has any instances (neither primary nor secondary), it’s easy to remove it from the cluster:
$ gnt-node remove NODE_NAME
This will deconfigure the node, stop the ganeti daemons on it and leave it hopefully like before it joined to the cluster.
The gnt-node modify -s command can be used to change the secondary IP of a node. This operation can only be performed if:
No instance is active on the target node
The new target IP is reachable from the master’s secondary IP
Also this operation will not allow to change a node from single-homed (same primary and secondary ip) to multi-homed (separate replication network) or vice versa, unless:
The target node is the master node and –force is passed.
The target cluster is single-homed and the new primary ip is a change to single homed for a particular node.
The target cluster is multi-homed and the new primary ip is a change to multi homed for a particular node.
For example to do a single-homed to multi-homed conversion:
$ gnt-node modify --force -s SECONDARY_IP MASTER_NAME
$ gnt-node modify -s SECONDARY_IP NODE1_NAME
$ gnt-node modify -s SECONDARY_IP NODE2_NAME
$ gnt-node modify -s SECONDARY_IP NODE3_NAME
...
The same commands can be used for multi-homed to single-homed except the secondary IPs should be the same as the primaries for each node, for that case.
When using LVM (either standalone or with DRBD), it can become tedious to debug and fix it in case of errors. Furthermore, even file-based storage can become complicated to handle manually on many hosts. Ganeti provides a couple of commands to help with automation.
This is a command specific to LVM handling. It allows listing the
logical volumes on a given node or on all nodes and their association to
instances via the volumes command:
$ gnt-node volumes
Node PhysDev VG Name Size Instance
node1 /dev/sdb1 xenvg e61fbc97-….disk0 512M instance17
node1 /dev/sdb1 xenvg ebd1a7d1-….disk0 512M instance19
node2 /dev/sdb1 xenvg 0af08a3d-….disk0 512M instance20
node2 /dev/sdb1 xenvg cc012285-….disk0 512M instance16
node2 /dev/sdb1 xenvg f0fac192-….disk0 512M instance18
The above command maps each logical volume to a volume group and underlying physical volume and (possibly) to an instance.
Added in version 2.1.
Starting with Ganeti 2.1, a new storage framework has been implemented that tries to abstract the handling of the storage type the cluster uses.
First is listing the backend storage and their space situation:
$ gnt-node list-storage
Node Type Name Size Used Free Allocatable
node1 lvm-vg xenvg 3.6T 0M 3.6T Y
node2 lvm-vg xenvg 3.6T 0M 3.6T Y
node3 lvm-vg xenvg 3.6T 2.0G 3.6T Y
The default is to list LVM physical volumes. It’s also possible to list the LVM volume groups:
$ gnt-node list-storage -t lvm-vg
Node Type Name Size Used Free Allocatable
node1 lvm-vg xenvg 3.6T 0M 3.6T Y
node2 lvm-vg xenvg 3.6T 0M 3.6T Y
node3 lvm-vg xenvg 3.6T 2.0G 3.6T Y
Next is repairing storage units, which is currently only implemented for
volume groups and does the equivalent of vgreduce --removemissing:
$ gnt-node repair-storage node2 lvm-vg xenvg
Sun Oct 25 22:21:45 2009 Repairing storage unit 'xenvg' on node2 ...
Last is the modification of volume properties, which is (again) only
implemented for LVM physical volumes and allows toggling the
allocatable value:
$ gnt-node modify-storage --allocatable=no node2 lvm-pv /dev/sdb1
All these commands are needed when recovering a node from a disk failure:
first, we need to recover from complete LVM failure (due to missing
disk), by running the repair-storage command
second, we need to change allocation on any partially-broken disk
(i.e. LVM still sees it, but it has bad blocks) by running
modify-storage
then we can evacuate the instances as needed
Beside the cluster initialisation command (which is detailed in the Ganeti installation tutorial document) and the master failover command which is explained under node handling, there are a couple of other cluster operations available.
One of the few commands that can be run on any node (not only the
master) is the getmaster command:
# on node2
$ gnt-cluster getmaster
node1.example.com
It is possible to query and change global cluster parameters via the
info and modify commands:
$ gnt-cluster info
Cluster name: cluster.example.com
Cluster UUID: 07805e6f-f0af-4310-95f1-572862ee939c
Creation time: 2009-09-25 05:04:15
Modification time: 2009-10-18 22:11:47
Master node: node1.example.com
Architecture (this node): 64bit (x86_64)
…
Tags: foo
Default hypervisor: xen-pvm
Enabled hypervisors: xen-pvm
Hypervisor parameters:
- xen-pvm:
root_path: /dev/sda1
…
Cluster parameters:
- candidate pool size: 10
…
Default instance parameters:
- default:
memory: 128
…
Default nic parameters:
- default:
link: xen-br0
…
There various parameters above can be changed via the modify
commands as follows:
the hypervisor parameters can be changed via modify -H
xen-pvm:root_path=…, and so on for other hypervisors/key/values
the “default instance parameters” are changeable via modify -B
parameter=value… syntax
the cluster parameters are changeable via separate options to the
modify command (e.g. --candidate-pool-size, etc.)
For detailed option list see the gnt-cluster(8) man page.
The cluster version can be obtained via the version command:
$ gnt-cluster version
Software version: 2.1.0
Internode protocol: 20
Configuration format: 2010000
OS api version: 15
Export interface: 0
This is not very useful except when debugging Ganeti.
There are two commands provided for replicating files to all nodes of a cluster and for running commands on all the nodes:
$ gnt-cluster copyfile /path/to/file
$ gnt-cluster command ls -l /path/to/file
These are simple wrappers over scp/ssh and more advanced usage can be obtained using dsh(1) and similar commands. But they are useful to update an OS script from the master node, for example.
There are three commands that relate to global cluster checks. The first
one is verify which gives an overview on the cluster state,
highlighting any issues. In normal operation, this command should return
no ERROR messages:
$ gnt-cluster verify
Sun Oct 25 23:08:58 2009 * Verifying global settings
Sun Oct 25 23:08:58 2009 * Gathering data (2 nodes)
Sun Oct 25 23:09:00 2009 * Verifying node status
Sun Oct 25 23:09:00 2009 * Verifying instance status
Sun Oct 25 23:09:00 2009 * Verifying orphan volumes
Sun Oct 25 23:09:00 2009 * Verifying remaining instances
Sun Oct 25 23:09:00 2009 * Verifying N+1 Memory redundancy
Sun Oct 25 23:09:00 2009 * Other Notes
Sun Oct 25 23:09:00 2009 - NOTICE: 5 non-redundant instance(s) found.
Sun Oct 25 23:09:00 2009 * Hooks Results
The second command is verify-disks, which checks that the instance’s
disks have the correct status based on the desired instance state
(up/down):
$ gnt-cluster verify-disks
Note that this command will show no output when disks are healthy.
The last command is used to repair any discrepancies in Ganeti’s recorded disk size and the actual disk size (disk size information is needed for proper activation and growth of DRBD-based disks):
$ gnt-cluster repair-disk-sizes
Sun Oct 25 23:13:16 2009 - INFO: Disk 0 of instance instance1 has mismatched size, correcting: recorded 512, actual 2048
Sun Oct 25 23:13:17 2009 - WARNING: Invalid result from node node4, ignoring node results
The above shows one instance having wrong disk size, and a node which returned invalid data, and thus we ignored all primary instances of that node.
If the verify command complains about file mismatches between the master
and other nodes, due to some node problems or if you manually modified
configuration files, you can force an push of the master configuration
to all other nodes via the redist-conf command:
$ gnt-cluster redist-conf
This command will be silent unless there are problems sending updates to the other nodes.
It is possible to rename a cluster, or to change its IP address, via the
rename command. If only the IP has changed, you need to pass the
current name and Ganeti will realise its IP has changed:
$ gnt-cluster rename cluster.example.com
This will rename the cluster to 'cluster.example.com'. If
you are connected over the network to the cluster name, the operation
is very dangerous as the IP address will be removed from the node and
the change may not go through. Continue?
y/[n]/?: y
Failure: prerequisites not met for this operation:
Neither the name nor the IP address of the cluster has changed
In the above output, neither value has changed since the cluster initialisation so the operation is not completed.
The job queue execution in Ganeti 2.0 and higher can be inspected,
suspended and resumed via the queue command:
$ gnt-cluster queue info
The drain flag is unset
$ gnt-cluster queue drain
$ gnt-instance stop instance1
Failed to submit job for instance1: Job queue is drained, refusing job
$ gnt-cluster queue info
The drain flag is set
$ gnt-cluster queue undrain
This is most useful if you have an active cluster and you need to upgrade the Ganeti software, or simply restart the software on any node:
suspend the queue via queue drain
wait until there are no more running jobs via gnt-job list
restart the master or another node, or upgrade the software
resume the queue via queue undrain
Note
this command only stores a local flag file, and if you failover the master, it will not have effect on the new master.
The ganeti-watcher(8) is a program, usually scheduled via
cron, that takes care of cluster maintenance operations (restarting
downed instances, activating down DRBD disks, etc.). However, during
maintenance and troubleshooting, this can get in your way; disabling it
via commenting out the cron job is not so good as this can be
forgotten. Thus there are some commands for automated control of the
watcher: pause, info and continue:
$ gnt-cluster watcher info
The watcher is not paused.
$ gnt-cluster watcher pause 1h
The watcher is paused until Mon Oct 26 00:30:37 2009.
$ gnt-cluster watcher info
The watcher is paused until Mon Oct 26 00:30:37 2009.
$ ganeti-watcher -d
2009-10-25 23:30:47,984: pid=28867 ganeti-watcher:486 DEBUG Pause has been set, exiting
$ gnt-cluster watcher continue
The watcher is no longer paused.
$ ganeti-watcher -d
2009-10-25 23:31:04,789: pid=28976 ganeti-watcher:345 DEBUG Archived 0 jobs, left 0
2009-10-25 23:31:05,884: pid=28976 ganeti-watcher:280 DEBUG Got data from cluster, writing instance status file
2009-10-25 23:31:06,061: pid=28976 ganeti-watcher:150 DEBUG Data didn't change, just touching status file
$ gnt-cluster watcher info
The watcher is not paused.
The exact details of the argument to the pause command are available
in the manpage.
Note
this command only stores a local flag file, and if you failover the master, it will not have effect on the new master.
If the cluster parameter maintain_node_health is enabled (see the
manpage for gnt-cluster, the init and modify subcommands),
then the following will happen automatically:
the watcher will shutdown any instances running on offline nodes
the watcher will deactivate any DRBD devices on offline nodes
In the future, more actions are planned, so only enable this parameter if the nodes are completely dedicated to Ganeti; otherwise it might be possible to lose data due to auto-maintenance actions.
The usual method to cleanup a cluster is to run gnt-cluster destroy
however if the Ganeti installation is broken in any way then this will
not run.
It is possible in such a case to cleanup manually most if not all traces of a cluster installation by following these steps on all of the nodes:
Shutdown all instances. This depends on the virtualisation method used (Xen, KVM, etc.):
Xen: run
xl listandxl destroyon all the non-Domain-0 instancesKVM: kill all the KVM processes
chroot: kill all processes under the chroot mountpoints
If using DRBD, shutdown all DRBD minors (which should by at this time
no-longer in use by instances); on each node, run drbdsetup
/dev/drbdN down for each active DRBD minor.
If using LVM, cleanup the Ganeti volume group; if only Ganeti created
logical volumes (and you are not sharing the volume group with the
OS, for example), then simply running lvremove -f xenvg (replace
‘xenvg’ with your volume group name) should do the required cleanup.
If using file-based storage, remove recursively all files and
directories under your file-storage directory: rm -rf
/srv/ganeti/file-storage/* replacing the path with the correct path
for your cluster.
Stop the ganeti daemons (/etc/init.d/ganeti stop) and kill any
that remain alive (pgrep ganeti and pkill ganeti).
Remove the ganeti state directory (rm -rf /var/lib/ganeti/*),
replacing the path with the correct path for your installation.
If using RBD, run rbd unmap /dev/rbdN to unmap the RBD disks.
Then remove the RBD disk images used by Ganeti, identified by their
UUIDs (rbd rm uuid.rbd.diskN).
On the master node, remove the cluster from the master-netdev (usually
xen-br0 for bridged mode, otherwise eth0 or similar), by running
ip a del $clusterip/32 dev xen-br0 (use the correct cluster ip and
network device name).
At this point, the machines are ready for a cluster creation; in case you want to remove Ganeti completely, you need to also undo some of the SSH changes and log directories:
rm -rf /var/log/ganeti /srv/ganeti (replace with the correct
paths)
remove from /root/.ssh the keys that Ganeti added (check the
authorized_keys and id_dsa files)
regenerate the host’s SSH keys (check the OpenSSH startup scripts)
uninstall Ganeti
Otherwise, if you plan to re-create the cluster, you can just go ahead
and rerun gnt-cluster init.
Ganeti uses both SSL and SSH keys, and actively modifies the SSH keys on the nodes. As result, in order to replace these keys, a few extra steps need to be followed: Cluster Keys Replacement
Ganeti comes with a comprehensive list of hypervisor parameters (called
hvparams internally) which can be set at cluster or instance level.
For now, this section will only cover KVM and only the most important ones. Please refer to the ganeti-instance(8) man page for a complete documentation.
On cluster level, parameters can be changed using the gnt-cluster command:
$ gnt-cluster modify -H kvm:param1=value,param2=value
On instance level, please use gnt-instance:abbr:
$ gnt-instance modify -H param1=value,param2=value
By default KVM will emulate the qemu64 CPU type. This CPU lacks many
features/flags of modern CPUs and recent Linux versions or Windows guests
might even refuse/fail to boot.
However, this will ensure maximum compatibilty for live migration between nodes with different CPU types. In general you should aim to have a homogenous cluster with matching CPU types. If that is the case, you can simply pass through the node’s CPU type/model and provide your instances with all features of your hardware.
$ gnt-cluster modify -H kvm:cpu_type=host
If you have CPUs of different generations in your cluster, you need to find the oldest one and configure this as the common denominator.
You can query your qemu version which CPU types it knows:
$ qemu-system-x86_64 -cpu help
You can then use gnt-cluster command to test the CPU types against all
your nodes and choose one that works on all of them (replace $CPU_TYPE
with e.g. EPYC-v3 or Cooperlake).
$ gnt-cluster command ‘qemu-system-x86_64 -cpu $CPU_TYPE,+pcid,+ssbd,+md-clear,enforce -machine accel=kvm -nographic -nodefaults -boot c,reboot-timeout=1 -no-reboot’
You can then proceed and set cpu_type accordingly:
$ gnt-cluster modify -H kvm:cpu_type=Cooperlake
Ganeti offers multiple options to access your instance. If your Instance
supports it, you can enable the serial console with the serial_console
parameter. You can access your console from the master node using
$ gnt-instance console %INSTANCE%
When you use direct kernel boot (e.g. kernel_path points to a kernel on
your node) Ganeti will automatically append serial options to the kernel_args
parameter. If you use a fully virtualized KVM boot, make sure to configure
serial parameters inside your instance (e.g. through GRUB).
If you would like to use a graphical console, you can either enable VNC or Spice. While the latter has improved performance, the first has a wider range of clients available.
To enable Spice, you need to configure spice_bind and set it either to
a valid listening IPv4/IPv6 address (including 0.0.0.0 or 127.0.0.1) or the
name of a network interface. Please check out all other spice_* parameters
in the gnt-instance(8) man pageto configure TLS, set compression
etc.
To enable VNC, you need to configure vnc_bind_address. This parameter only
allows IPv4 addresses to be specified. Please check out all other vnc_*
parameters in the gnt-instance(8) man page.
Please keep in mind that you can always configure the serial console but VNC
and Spice only work exclusively. Configuring both will result in an error from
gnt-instance or gnt-cluster.
Ganeti supports both disk I/O modes threads and native and they can be
controlled through the disk_aio parameter. In most cases native seems
to perforem better, however threads is still Ganeti’s default.
If you care about reliable storage, we recommend setting disk_cache to
none, but depending on your usecase you should also look into the other
possible values listed and explained in gnt-instance(8).
If you are using a storage backend that permits live migration (e.g. drbd,
rbd or sharedfile) you may want to look at the relevant parameters.
migration_bandwidth sets the amount of bandwidth QEMU is allowed to use
for memory transfers (in megabyte/second) and migration_downtime sets
the amount of time an instance is allowed to be frozen to transfer the remainding
memory (in milliseconds). Keep in mind if your instance’s memory changes fast
and the migration downtime window is too small a live migration might run endlessly.
At the same time, setting the migration downtime window to a larger value might
break or at least confuse the software running in your instance.
If you have configured your cluster to use a separate network for replication traffic, live migration traffic will use that network as well.
You may also use postcopy-ram migration which means that an instance will
migrate early over to the secondary node and fetch the remaining memory from
the source afterwards. Keep in mind that regular migration will copy memory first
and only migrate the instance over if that succeeds. If the destination node
dies in the process, the instance will not be touched by this and keep running
on the source node. With the postcopy method both nodes need to stay alive
until everything has been transferred, otherwise the instance will die.
Ganeti defaults to using VirtIO devices for disks and networking. If an instance
requires it, you may also switch the disk type to IDE or SCSI or emulate certain
NIC types like e1000. Please check the gnt-instance(8) man page for
the parameters disk_type and nic_type for all possible values. The setting
always applies to all disks and NICs for a given instance.
While setting up the details of the storage options is generally out of scope for this document, there are some tips that we can share with you
If you run your DRBD replication across 10Gbe links or faster, the default settings will usually prevent you from saturating those links. The following settings have proven to speed up things. Please keep in mind that any changes to these parameters will not affect running instances.
$ gnt-cluster modify –disk-parameters drbd:disk-barriers=n,protocol=C $ gnt-cluster modify –disk-parameters drbd:dynamic-resync=true,c-plan-ahead=20,c-min-rate=104857600,c-max-rate=1073741824 $ gnt-cluster modify –disk-parameters drbd:net-custom=’–max-buffers=16000 –max-epoch-size=16000’
With GlusterFS or RBD in combination with KVM you have the option to either use
kernelspace access (through blockdevices) or through userspace implementations
provided by QEMU. The latter will possibly speed things up. You can switch the
access mode through gnt-cluster (default is kernelspace):
$ gnt-cluster modify –disk-parameters rbd:access=userspace
Starting with Ganeti 2.8, a monitoring daemon is available, providing information about the status and the performance of the system.
The monitoring daemon runs on every node, listening on TCP port 1815. Each instance of the daemon provides information related to the node it is running on.
The queries to the monitoring agent will be HTTP GET requests on port 1815. The answer will be encoded in JSON format and will depend on the specific accessed resource.
If a request is sent to a non-existing resource, a 404 error will be returned by the HTTP server.
The following paragraphs will present the existing resources supported by the current protocol version, that is version 1.
/¶The root resource. It will return the list of the supported protocol version numbers.
Currently, this will include only version 1.
/1¶Not an actual resource per-se, it is the root of all the resources of protocol version 1.
If requested through GET, the null JSON value will be returned.
/1/list/collectors¶Returns a list of tuples (kind, category, name) showing all the collectors available in the system.
/1/report/all¶A list of the reports of all the data collectors, as a JSON list.
Status reporting collectors will provide their output in non-verbose format.
The verbose format can be requested by adding the parameter verbose=1 to the
request.
/1/report/[category]/[collector_name]¶Returns the report of the collector [collector_name] that belongs to the
specified [category].
The category has to be written in lowercase.
If a collector does not belong to any category, default will have to be
used as the value for [category].
Status reporting collectors will provide their output in non-verbose format.
The verbose format can be requested by adding the parameter verbose=1 to the
request.
The tool harep can be used to automatically fix some problems that are
present in the cluster.
It is mainly meant to be regularly and automatically executed
as a cron job. This is quite evident by considering that, when executed, it does
not immediately fix all the issues of the instances of the cluster, but it
cycles the instances through a series of states, one at every harep
execution. Every state performs a step towards the resolution of the problem.
This process goes on until the instance is brought back to the healthy state,
or the tool realizes that it is not able to fix the instance, and
therefore marks it as in failure state.
By default, harep checks the status of the cluster but it is not allowed to
perform any modification. Modification must be explicitly allowed by an
appropriate use of tags. Tagging can be applied at various levels, and can
enable different kinds of autorepair, as hereafter described.
All the tags that authorize harep to perform modifications follow this
syntax:
ganeti:watcher:autorepair:<type>
where <type> indicates the kind of intervention that can be performed. Every
possible value of <type> includes at least all the authorization of the
previous one, plus its own. The possible values, in increasing order of
severity, are:
fix-storage allows a disk replacement or another operation that
fixes the instance backend storage without affecting the instance
itself. This can for example recover from a broken drbd secondary, but
risks data loss if something is wrong on the primary but the secondary
was somehow recoverable.
migrate allows an instance migration. This can recover from a
drained primary, but can cause an instance crash in some cases (bugs).
failover allows instance reboot on the secondary. This can recover
from an offline primary, but the instance will lose its running state.
reinstall allows disks to be recreated and an instance to be
reinstalled. This can recover from primary&secondary both being
offline, or from an offline primary in the case of non-redundant
instances. It causes data loss.
These autorepair tags can be applied to a cluster, a nodegroup or an instance, and will act where they are applied and to everything in the entities sub-tree (e.g. a tag applied to a nodegroup will apply to all the instances contained in that nodegroup, but not to the rest of the cluster).
If there are multiple ganeti:watcher:autorepair:<type> tags in an
object (cluster, node group or instance), the least destructive tag
takes precedence. When multiplicity happens across objects, the nearest
tag wins. For example, if in a cluster with two instances, I1 and
I2, I1 has failover, and the cluster itself has both
fix-storage and reinstall, I1 will end up with failover
and I2 with fix-storage.
Sometimes it is useful to stop harep from performing its task temporarily, and it is useful to be able to do so without disrupting its configuration, that is, without removing the authorization tags. In order to do this, suspend tags are provided.
Suspend tags can be added to cluster, nodegroup or instances, and act on the
entire entities sub-tree. No operation will be performed by harep on the
instances protected by a suspend tag. Their syntax is as follows:
ganeti:watcher:autorepair:suspend[:<timestamp>]
If there are multiple suspend tags in an object, the form without timestamp takes precedence (permanent suspension); or, if all object tags have a timestamp, the one with the highest timestamp.
Tags with a timestamp will be automatically removed when the time indicated by the timestamp is passed. Indefinite suspension tags have to be removed manually.
Harep will report about the result of its actions both through its CLI, and by adding tags to the instances it operated on. Such tags will follow the syntax hereby described:
ganeti:watcher:autorepair:result:<type>:<id>:<timestamp>:<result>:<jobs>
If this tag is present a repair of type type has been performed on
the instance and has been completed by timestamp. The result is
either success, failure or enoperm, and jobs is a
+-separated list of jobs that were executed for this repair.
An enoperm result is an error state due to permission problems. It
is returned when the repair cannot proceed because it would require to perform
an operation that is not allowed by the ganeti:watcher:autorepair:<type> tag
that is defining the instance autorepair permissions.
NB: if an instance repair ends up in a failure state, it will not be touched
again by harep until it has been manually fixed by the system administrator
and the ganeti:watcher:autorepair:result:failure:* tag has been manually
removed.
The various jobs submitted by the instance/node/cluster commands can be
examined, canceled and archived by various invocations of the
gnt-job command.
First is the job list command:
$ gnt-job list
17771 success INSTANCE_QUERY_DATA
17773 success CLUSTER_VERIFY_DISKS
17775 success CLUSTER_REPAIR_DISK_SIZES
17776 error CLUSTER_RENAME(cluster.example.com)
17780 success CLUSTER_REDIST_CONF
17792 success INSTANCE_REBOOT(instance1.example.com)
More detailed information about a job can be found via the info
command:
$ gnt-job info 17776
Job ID: 17776
Status: error
Received: 2009-10-25 23:18:02.180569
Processing start: 2009-10-25 23:18:02.200335 (delta 0.019766s)
Processing end: 2009-10-25 23:18:02.279743 (delta 0.079408s)
Total processing time: 0.099174 seconds
Opcodes:
OP_CLUSTER_RENAME
Status: error
Processing start: 2009-10-25 23:18:02.200335
Processing end: 2009-10-25 23:18:02.252282
Input fields:
name: cluster.example.com
Result:
OpPrereqError
[Neither the name nor the IP address of the cluster has changed]
Execution log:
During the execution of a job, it’s possible to follow the output of a
job, similar to the log that one get from the gnt- commands, via the
watch command:
$ gnt-instance add --submit … instance1
JobID: 17818
$ gnt-job watch 17818
Output from job 17818 follows
-----------------------------
Mon Oct 26 00:22:48 2009 - INFO: Selected nodes for instance instance1 via iallocator dumb: node1, node2
Mon Oct 26 00:22:49 2009 * creating instance disks...
Mon Oct 26 00:22:52 2009 adding instance instance1 to cluster config
Mon Oct 26 00:22:52 2009 - INFO: Waiting for instance instance1 to sync disks.
…
Mon Oct 26 00:23:03 2009 creating os for instance instance1 on node node1
Mon Oct 26 00:23:03 2009 * running the instance OS create scripts...
Mon Oct 26 00:23:13 2009 * starting instance...
$
This is useful if you need to follow a job’s progress from multiple terminals.
A job that has not yet started to run can be canceled:
$ gnt-job cancel 17810
But not one that has already started execution:
$ gnt-job cancel 17805
Job 17805 is no longer waiting in the queue
There are two queues for jobs: the current and the archive
queue. Jobs are initially submitted to the current queue, and they stay
in that queue until they have finished execution (either successfully or
not). At that point, they can be moved into the archive queue using e.g.
gnt-job autoarchive all. The ganeti-watcher script will do this
automatically 6 hours after a job is finished. The ganeti-cleaner
script will then remove archived the jobs from the archive directory
after three weeks.
Note that gnt-job list only shows jobs in the current queue.
Archived jobs can be viewed using gnt-job info <id>.
Since Ganeti 2.4, it is possible to extend the Ganeti deployment with two custom scenarios: Ganeti inside Ganeti and multi-site model.
It is sometimes useful to be able to use a Ganeti instance as a Ganeti node (part of another cluster, usually). One example scenario is two small clusters, where we want to have an additional master candidate that holds the cluster configuration and can be used for helping with the master voting process.
However, these Ganeti instance should not host instances themselves, and
should not be considered in the normal capacity planning, evacuation
strategies, etc. In order to accomplish this, mark these nodes as
non-vm_capable:
$ gnt-node modify --vm-capable=no node3
The vm_capable status can be listed as usual via gnt-node list:
$ gnt-node list -oname,vm_capable
Node VMCapable
node1 Y
node2 Y
node3 N
When this flag is set, the cluster will not do any operations that relate to instances on such nodes, e.g. hypervisor operations, disk-related operations, etc. Basically they will just keep the ssconf files, and if master candidates the full configuration.
If Ganeti is deployed in multi-site model, with each site being a node group (so that instances are not relocated across the WAN by mistake), it is conceivable that either the WAN latency is high or that some sites have a lower reliability than others. In this case, it doesn’t make sense to replicate the job information across all sites (or even outside of a “central” node group), so it should be possible to restrict which nodes can become master candidates via the auto-promotion algorithm.
Ganeti 2.4 introduces for this purpose a new master_capable flag,
which (when unset) prevents nodes from being marked as master
candidates, either manually or automatically.
As usual, the node modify operation can change this flag:
$ gnt-node modify --auto-promote --master-capable=no node3
Fri Jan 7 06:23:07 2011 - INFO: Demoting from master candidate
Fri Jan 7 06:23:08 2011 - INFO: Promoted nodes to master candidate role: node4
Modified node node3
- master_capable -> False
- master_candidate -> False
And the node list operation will list this flag:
$ gnt-node list -oname,master_capable node1 node2 node3
Node MasterCapable
node1 Y
node2 Y
node3 N
Note that marking a node both not vm_capable and not
master_capable makes the node practically unusable from Ganeti’s
point of view. Hence these two flags should be used probably in
contrast: some nodes will be only master candidates (master_capable but
not vm_capable), and other nodes will only hold instances (vm_capable
but not master_capable).
Beside the usual gnt- and ganeti- commands which are provided
and installed in $prefix/sbin at install time, there are a couple of
other tools installed which are used seldom but can be helpful in some
cases.
The lvmstrap tool, introduced in Configuring LVM section,
has two modes of operation:
diskinfo shows the discovered disks on the system and their status
create takes all not-in-use disks and creates a volume group out
of them
Warning
The create argument to this command causes data-loss!
The cfgupgrade tools is used to upgrade between major (and minor)
Ganeti versions, and to roll back. Point-releases are usually
transparent for the admin.
More information about the upgrade procedure is listed on the wiki at http://code.google.com/p/ganeti/wiki/UpgradeNotes.
There is also a script designed to upgrade from Ganeti 1.2 to 2.0,
called cfgupgrade12.
Note
This command is not actively maintained; make sure you backup your configuration before using it
This can be used as an alternative to direct editing of the main configuration file if Ganeti has a bug and prevents you, for example, from removing an instance or a node from the configuration file.
Warning
This command will erase existing instances if given as arguments!
This tool is used to exercise either the hardware of machines or alternatively the Ganeti software. It is safe to run on an existing cluster as long as you don’t pass it existing instance names.
The command will, by default, execute a comprehensive set of operations against a list of instances, these being:
creation
disk replacement (for redundant instances)
failover and migration (for redundant instances)
move (for non-redundant instances)
disk growth
add disks, remove disk
add NICs, remove NICs
export and then import
rename
reboot
shutdown/startup
and finally removal of the test instances
Executing all these operations will test that the hardware performs well: the creation, disk replace, disk add and disk growth will exercise the storage and network; the migrate command will test the memory of the systems. Depending on the passed options, it can also test that the instance OS definitions are executing properly the rename, import and export operations.
This tool takes the Ganeti configuration and outputs a “sanitized” version, by randomizing or clearing:
DRBD secrets and cluster public key (always)
host names (optional)
IPs (optional)
OS names (optional)
LV names (optional, only useful for very old clusters which still have instances whose LVs are based on the instance name)
By default, all optional items are activated except the LV name
randomization. When passing --no-randomization, which disables the
optional items (i.e. just the DRBD secrets and cluster public keys are
randomized), the resulting file can be used as a safety copy of the
cluster config - while not trivial, the layout of the cluster can be
recreated from it and if the instance disks have not been lost it
permits recovery from the loss of all master candidates.
Ganeti can either be run entirely as root, or with every daemon running as
its own specific user (if the parameters --with-user-prefix and/or
--with-group-prefix have been specified at ./configure-time).
In case split users are activated, they are required to exist on the system, and they need to belong to the proper groups in order for the access permissions to files and programs to be correct.
The users-setup tool, when run, takes care of setting up the proper
users and groups.
When invoked without parameters, the tool runs in interactive mode, showing the list of actions it will perform and asking for confirmation before proceeding.
Providing the --yes-do-it parameter to the tool prevents the confirmation
from being asked, and the users and groups will be created immediately.
Below is a list (which might not be up-to-date) of additional projects that can be useful in a Ganeti deployment. They can be downloaded from the project site (http://www.ganeti.org) and the repositories are also on the project git site (https://github.com/ganeti).
The ganeti-nbma software is designed to allow instances to live on a
separate, virtual network from the nodes, and in an environment where
nodes are not guaranteed to be able to reach each other via multicasting
or broadcasting. For more information see the README in the source
archive.