Documents ganeti version 1.2
In order to allow customisation of operations, ganeti will run scripts under /etc/ganeti/hooks based on certain rules.
This is similar to the /etc/network/ structure present in Debian for network interface handling.
For every operation, two sets of scripts are run:
pre phase (for authorization/checking)
post phase (for logging)
Also, for each operation, the scripts are run on one or more nodes, depending on the operation type.
Note that, even though we call them scripts, we are actually talking about any executable.
The pre scripts have a definite target: to check that the operation is allowed given the site-specific constraints. You could have, for example, a rule that says every new instance is required to exists in a database; to implement this, you could write a script that checks the new instance parameters against your database.
The objective of these scripts should be their return code (zero or non-zero for success and failure). However, if they modify the environment in any way, they should be idempotent, as failed executions could be restarted and thus the script(s) run again with exactly the same parameters.
Note that if a node is unreachable at the time a hooks is run, this will not be interpreted as a deny for the execution. In other words, only an actual error returned from a script will cause abort, and not an unreachable node.
Therefore, if you want to guarantee that a hook script is run and denies an action, it's best to put it on the master node.
These scripts should do whatever you need as a reaction to the completion of an operation. Their return code is not checked (but logged), and they should not depend on the fact that the pre scripts have been run.
The allowed names for the scripts consist of (similar to run-parts(8)) upper and lower case, digits, underscores and hyphens. In other words, the regexp ^[a-zA-Z0-9_-]+$. Also, non-executable scripts will be ignored.
On a single node, the scripts in a directory are run in lexicographic order (more exactly, the python string comparison order). It is advisable to implement the usual NN-name convention where NN is a two digit number.
For an operation whose hooks are run on multiple nodes, there is no specific ordering of nodes with regard to hooks execution; you should assume that the scripts are run in parallel on the target nodes (keeping on each node the above specified ordering). If you need any kind of inter-node synchronisation, you have to implement it yourself in the scripts.
The scripts will be run as follows:
no command line arguments
no controlling tty
stdin is
actually /dev/null
stdout and
stderr are directed to
files
the PATH is reset to
/sbin:/bin:/usr/sbin:/usr/bin
the environment is cleared, and only ganeti-specific variables will be left
All informations about the cluster is passed using environment variables. Different operations will have sligthly different environments, but most of the variables are common.
Table 1. Operation list
| Operation ID | Directory prefix | Description | Command | Supported env. variables | pre hooks | post hooks |
|---|---|---|---|---|---|---|
| OP_INIT_CLUSTER | cluster-init | Initialises the cluster | gnt-cluster init | CLUSTER, MASTER | master node, cluster name | |
| OP_MASTER_FAILOVER | master-failover | Changes the master | gnt-cluster master-failover | OLD_MASTER, NEW_MASTER | the new master | all nodes |
| OP_ADD_NODE | node-add | Adds a new node to the cluster | gnt-node add | NODE_NAME, NODE_PIP, NODE_SIP | all existing nodes | all existing nodes plus the new node |
| OP_REMOVE_NODE | node-remove | Removes a node from the cluster | gnt-node remove | NODE_NAME | all existing nodes except the removed node | |
| OP_INSTANCE_ADD | instance-add | Creates a new instance | gnt-instance add | INSTANCE_NAME, INSTANCE_PRIMARY, INSTANCE_SECONDARIES, DISK_TEMPLATE, MEM_SIZE, DISK_SIZE, SWAP_SIZE, VCPUS, INSTANCE_IP, INSTANCE_ADD_MODE, SRC_NODE, SRC_PATH, SRC_IMAGE | master node, primary and secondary nodes | |
| OP_BACKUP_EXPORT | instance-export | Export the instance | gnt-backup export | INSTANCE_NAME, EXPORT_NODE, EXPORT_DO_SHUTDOWN | ||
| OP_INSTANCE_START | instance-start | Starts an instance | gnt-instance start | INSTANCE_NAME, INSTANCE_PRIMARY, INSTANCE_SECONDARIES, FORCE | ||
| OP_INSTANCE_SHUTDOWN | instance-shutdown | Stops an instance | gnt-instance shutdown | INSTANCE_NAME, INSTANCE_PRIMARY, INSTANCE_SECONDARIES | ||
| OP_INSTANCE_MODIFY | instance-modify | Modifies the instance parameters. | gnt-instance modify | INSTANCE_NAME, MEM_SIZE, VCPUS, INSTANCE_IP | ||
| OP_INSTANCE_FAILOVER | instance-failover | Failover an instance | gnt-instance start | INSTANCE_NAME, INSTANCE_PRIMARY, INSTANCE_SECONDARIES, IGNORE_CONSISTENCY | ||
| OP_INSTANCE_REMOVE | instance-remove | Remove an instance | gnt-instance remove | INSTANCE_NAME, INSTANCE_PRIMARY, INSTANCE_SECONDARIES | master node | |
| OP_INSTANCE_ADD_MDDRBD | mirror-add | Adds a mirror component | gnt-instance add-mirror | INSTANCE_NAME, NEW_SECONDARY, DISK_NAME | ||
| OP_INSTANCE_REMOVE_MDDRBD | mirror-remove | Removes a mirror component | gnt-instance remove-mirror | INSTANCE_NAME, OLD_SECONDARY, DISK_NAME, DISK_ID | ||
| OP_INSTANCE_REPLACE_DISKS | mirror-replace | Replace all mirror components | gnt-instance replace-disks | INSTANCE_NAME, OLD_SECONDARY, NEW_SECONDARY | ||
Note that all variables listed here are actually prefixed
with GANETI_ in order to provide a
different namespace.
This is the list of environment variables supported by all operations:
Documents the hooks interface version. In case this doesnt match what the script expects, it should not run. The documents conforms to the version 1.
one of PRE or
POST denoting which phase are we
in.
the cluster name
the master node
one of the OP_* values from
the table of operations
one of INSTANCE, NODE, CLUSTER, showing the target of the operation.
This is the list of variables which are specific to one or more operations.
The name of the instance which is the target of the operation.
The disk type for the instance.
The (OS) disk size for the instance.
The name of the instance OS.
The name of the node which is the primary for the instance.
Space-separated list of secondary nodes for the instance.
The target node of this operation (not the node on which the hook runs).
The primary IP of the target node (the one over which inter-node communication is done).
The secondary IP of the target node (the one over which drbd replication is done). This can be equal to the primary ip, in case the cluster is not dual-homed.
The old, respectively the new master for the master failover operation.
This is provided by some operations when the user gave this flag.
The user has specified this flag. It is used when failing over instances in case the primary node is down.
The memory, disk, swap size and the number of processor selected for the instance (in gnt-instance add or gnt-instance modify).
If defined, the instance IP in the gnt-instance add and gnt-instance set commands. If not defined, it means that no IP has been defined.
The disk template type when creating the instance.
The mode of the create: either
create for create from scratch or
import for restoring from an
exported image.
In case the instance has been added by import, these variables are defined and point to the source node, source path (the directory containing the image and the config file) and the source disk image file.
The disk name (either sda or sdb) in mirror operations (add/remove mirror).
The disk id for mirror remove operations. You can look this up using gnt-instance info.
The name of the node on which the new mirror componet is being added. This can be the name of the current secondary, if the new mirror is on the same secondary.
The name of the old secondary. This is used in both replace-disks and remove-mirror. Note that this can be equal to the new secondary (only replace-disks has both variables) if the secondary node hasn't actually changed).
The node on which the exported image of the instance was done.
This variable tells if the instance has been shutdown or not while doing the export. In the "was shutdown" case, it's likely that the filesystem is consistent, whereas in the "did not shutdown" case, the filesystem would need a check (journal replay or full fsck) in order to guarantee consistency.