Documents Ganeti version 2.6
Contents
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 the its primary instances.
A node belonging to a cluster can be in one of the following roles at a given time:
Depending on the role, each node will run a set of daemons:
Beside the node role, there are other node flags that influence its behaviour:
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 five disk templates you can choose from:
Note
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.
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.
Tags are short strings that can be attached to either to cluster itself, or to nodes or instances. They are useful as a very simplistic information store for helping with cluster administration, for example by attaching owner information to each instance after it’s created:
$ gnt-instance add … instance1
$ gnt-instance add-tags instance1 owner:user2
And then by listing each instance and its tags, this information could be used for contacting the users of each instance.
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 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:
See the manpage for gnt-instance 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 minumum 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 xm shutdown or xm destroy on an instance Ganeti will automatically restart it (via the ganeti-watcher command which is launched via cron).
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:
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:
While pygrub is deprecated, here is how you can configure it:
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:
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 at 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:
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 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:
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.
New 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.
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 -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 -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).
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:
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.
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.
New 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 Name Size Used Free
node1 /dev/sda7 673.8G 0M 673.8G
node1 /dev/sdb1 698.6G 1.5G 697.1G
node2 /dev/sda7 673.8G 0M 673.8G
node2 /dev/sdb1 698.6G 1.0G 697.6G
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 Name Size
node1 xenvg 1.3T
node2 xenvg 1.3T
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:
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:
For detailed option list see the gnt-cluster(8) man page.
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:
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 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:
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:
- Xen: run xm list and xm destroy on all the non-Domain-0 instances
- KVM: kill all the KVM processes
- chroot: kill all processes under the chroot mountpoints
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:
Otherwise, if you plan to re-create the cluster, you can just go ahead and rerun gnt-cluster init.
The tags handling (addition, removal, listing) is similar for all the objects that support it (instances, nodes, and the cluster).
Note that the set of characters present in a tag and the maximum tag length are restricted. Currently the maximum length is 128 characters, there can be at most 4096 tags per object, and the set of characters is comprised by alphanumeric characters and additionally .+*/:@-.
Tags can be added via add-tags:
$ gnt-instance add-tags INSTANCE a b c
$ gnt-node add-tags INSTANCE a b c
$ gnt-cluster add-tags a b c
The above commands add three tags to an instance, to a node and to the cluster. Note that the cluster command only takes tags as arguments, whereas the node and instance commands first required the node and instance name.
Tags can also be added from a file, via the --from=FILENAME argument. The file is expected to contain one tag per line.
Tags can also be remove via a syntax very similar to the add one:
$ gnt-instance remove-tags INSTANCE a b c
And listed via:
$ gnt-instance list-tags
$ gnt-node list-tags
$ gnt-cluster list-tags
It is also possible to execute a global search on the all tags defined in the cluster configuration, via a cluster command:
$ gnt-cluster search-tags REGEXP
The parameter expected is a regular expression (see regex(7)). This will return all tags that match the search, together with the object they are defined in (the names being show in a hierarchical kind of way):
$ gnt-cluster search-tags o
/cluster foo
/instances/instance1 owner:bar
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:
Warning
The create argument to this command causes data-loss!
The cfgupgrade tools is used to upgrade between major (and minor) Ganeti versions. 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:
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:
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.
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://code.google.com/p/ganeti/) and the repositories are also on the project git site (http://git.ganeti.org).
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.
Before Ganeti version 2.5, this was a standalone project; since that version it is integrated into the Ganeti codebase (see Ganeti quick installation guide for instructions on how to enable it). If you run an older Ganeti version, you will have to download and build it separately.
For more information and installation instructions, see the README file in the source archive.