The ganeti-watcher is a periodically run script which is responsible for keeping the instances in the correct status. It has two separate functions, one for the master node and another one that runs on every node.
Its primary function is to try to keep running all instances which are marked as up in the configuration file, by trying to start them a limited number of times.
Its other function is to "repair" DRBD links by reactivating the block devices of instances which have secondaries on nodes that have been rebooted.
The watcher will restart any down daemons that are appropriate for the current node.
In addition, it will execute any scripts which exist under the "watcher" directory in the ganeti hooks directory (/usr/local/etc/ganeti/hooks). This should be used for lightweight actions, like starting any extra daemons.
If the cluster parameter maintain_node_health is enabled, then the watcher will also shutdown instances and DRBD devices if the node is declared as offline by known master candidates.
The watcher does synchronous queries but will submit jobs for executing the changes. Due to locking, it could be that the jobs execute much later than the watcher executes them.
The command has a state file located at /usr/local/var/lib/ganeti/watcher.data (only used on the master) and a log file at /usr/local/var/log/ganeti/watcher.log. Removal of either file will not affect correct operation; the removal of the state file will just cause the restart counters for the instances to reset to zero.
Report bugs to http://code.google.com/p/ganeti/ or contact the developers using the ganeti mailing list <ganeti@googlegroups.com>.
Ganeti overview and specifications: ganeti(7) (general overview), ganeti-os-interface(7) (guest OS definitions).
Ganeti commands: gnt-cluster(8) (cluster-wide commands), gnt-job(8) (job-related commands), gnt-node(8) (node-related commands), gnt-instance(8) (instance commands), gnt-os(8) (guest OS commands), gnt-backup(8) (instance import/export commands), gnt-debug(8) (debug commands).
Ganeti daemons: ganeti-watcher(8) (automatic instance restarter), ganeti-cleaner(8) (job queue cleaner), ganeti-noded(8) (node daemon), ganeti-masterd(8) (master daemon), ganeti-rapi(8) (remote API daemon).
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