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Ganeti customisation using hooks

================================

Documents ganeti version 2.0

.. contents::

Introduction

------------

In order to allow customisation of operations, ganeti runs scripts

under ``/etc/ganeti/hooks`` based on certain rules.

This is similar to the ``/etc/network/`` structure present in Debian

for network interface handling.

Organisation

------------

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.

*pre* scripts

~~~~~~~~~~~~~

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.

*post* scripts

~~~~~~~~~~~~~~

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.

Naming

~~~~~~

The allowed names for the scripts consist of (similar to *run-parts* )

upper and lower case, digits, underscores and hyphens. In other words,

the regexp ``^[a-zA-Z0-9_-]+$``. Also, non-executable scripts will be

ignored.

Order of execution

~~~~~~~~~~~~~~~~~~

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.

Execution environment

~~~~~~~~~~~~~~~~~~~~~

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

- PATH is reset to ``/sbin:/bin:/usr/sbin:/usr/bin``

- the environment is cleared, and only ganeti-specific variables will

  be left

All information about the cluster is passed using environment

variables. Different operations will have sligthly different

environments, but most of the variables are common.

Operation list

--------------

Node operations

~~~~~~~~~~~~~~~

OP_ADD_NODE

+++++++++++

Adds a node to the cluster.

:directory: node-add

:env. vars: NODE_NAME, NODE_PIP, NODE_SIP

:pre-execution: all existing nodes

:post-execution: all nodes plus the new node

OP_REMOVE_NODE

++++++++++++++

Removes a node from the cluster.

:directory: node-remove

:env. vars: NODE_NAME

:pre-execution: all existing nodes except the removed node

:post-execution: all existing nodes except the removed node

OP_NODE_SET_PARAMS

++++++++++++++++++

Changes a node's parameters.

:directory: node-modify

:env. vars: MASTER_CANDIDATE, OFFLINE, DRAINED

:pre-execution: master node, the target node

:post-execution: master node, the target node

Instance operations

~~~~~~~~~~~~~~~~~~~

All instance operations take at least the following variables:

INSTANCE_NAME, INSTANCE_PRIMARY, INSTANCE_SECONDARIES,

INSTANCE_OS_TYPE, INSTANCE_DISK_TEMPLATE, INSTANCE_MEMORY,

INSTANCE_DISK_SIZES, INSTANCE_VCPUS, INSTANCE_NIC_COUNT,

INSTANCE_NICn_IP, INSTANCE_NICn_BRIDGE, INSTANCE_NICn_MAC,

INSTANCE_DISK_COUNT, INSTANCE_DISKn_SIZE, INSTANCE_DISKn_MODE.

The INSTANCE_NICn_* and INSTANCE_DISKn_* variables represent the

properties of the *n* -th NIC and disk, and are zero-indexed.

OP_INSTANCE_ADD

+++++++++++++++

Creates a new instance.

:directory: instance-add

:env. vars: ADD_MODE, SRC_NODE, SRC_PATH, SRC_IMAGES

:pre-execution: master node, primary and secondary nodes

:post-execution: master node, primary and secondary nodes

OP_INSTANCE_REINSTALL

+++++++++++++++++++++

Reinstalls an instance.

:directory: instance-reinstall

:env. vars: only the standard instance vars

:pre-execution: master node, primary and secondary nodes

:post-execution: master node, primary and secondary nodes

OP_BACKUP_EXPORT

++++++++++++++++

Exports the instance.

:directory: instance-export

:env. vars: EXPORT_NODE, EXPORT_DO_SHUTDOWN

:pre-execution: master node, primary and secondary nodes

:post-execution: master node, primary and secondary nodes

OP_INSTANCE_START

+++++++++++++++++

Starts an instance.

:directory: instance-start

:env. vars: INSTANCE_NAME, INSTANCE_PRIMARY, INSTANCE_SECONDARIES, FORCE

:pre-execution: master node, primary and secondary nodes

:post-execution: master node, primary and secondary nodes

OP_INSTANCE_SHUTDOWN

++++++++++++++++++++

Stops an instance.

:directory: instance-shutdown

:env. vars: INSTANCE_NAME, INSTANCE_PRIMARY, INSTANCE_SECONDARIES

:pre-execution: master node, primary and secondary nodes

:post-execution: master node, primary and secondary nodes

OP_INSTANCE_REBOOT

++++++++++++++++++

Reboots an instance.

:directory: instance-reboot

:env. vars: IGNORE_SECONDARIES, REBOOT_TYPE

:pre-execution: master node, primary and secondary nodes

:post-execution: master node, primary and secondary nodes

OP_INSTANCE_MODIFY

++++++++++++++++++

Modifies the instance parameters.

:directory: instance-modify

:env. vars: INSTANCE_NAME, MEM_SIZE, VCPUS, INSTANCE_IP

:pre-execution: master node, primary and secondary nodes

:post-execution: master node, primary and secondary nodes

OP_INSTANCE_FAILOVER

++++++++++++++++++++

Failovers an instance.

:directory: instance-failover

:env. vars: IGNORE_CONSISTENCY

:pre-execution: master node, secondary node

:post-execution: master node, secondary node

OP_INSTANCE_MIGRATE

++++++++++++++++++++

Migrates an instance.

:directory: instance-failover

:env. vars: INSTANCE_MIGRATE_LIVE, INSTANCE_MIGRATE_CLEANUP

:pre-execution: master node, secondary node

:post-execution: master node, secondary node

OP_INSTANCE_REMOVE

++++++++++++++++++

Remove an instance.

:directory: instance-remove

:env. vars: INSTANCE_NAME, INSTANCE_PRIMARY, INSTANCE_SECONDARIES

:pre-execution: master node

:post-execution: master node

OP_INSTANCE_REPLACE_DISKS

+++++++++++++++++++++++++

Replace an instance's disks.

:directory: mirror-replace

:env. vars: MODE, NEW_SECONDARY, OLD_SECONDARY

:pre-execution: master node, primary and secondary nodes

:post-execution: master node, primary and secondary nodes

OP_INSTANCE_GROW_DISK

+++++++++++++++++++++

Grows the disk of an instance.

:directory: disk-grow

:env. vars: DISK, AMOUNT

:pre-execution: master node, primary node

:post-execution: master node, primary node

OP_INSTANCE_RENAME

++++++++++++++++++

Renames an instance.

:directory: instance-rename

:env. vars: INSTANCE_NEW_NAME

:pre-execution: master node, primary and secondary nodes

:post-execution: master node, primary and secondary nodes

Cluster operations

~~~~~~~~~~~~~~~~~~

OP_CLUSTER_VERIFY

+++++++++++++++++

Verifies the cluster status. This is a special LU with regard to

hooks, as the result of the opcode will be combined with the result of

post-execution hooks, in order to allow administrators to enhance the

cluster verification procedure.

:directory: cluster-verify

:env. vars: CLUSTER, MASTER, CLUSTER_TAGS, NODE_TAGS_<name>

:pre-execution: none

:post-execution: all nodes

OP_CLUSTER_RENAME

+++++++++++++++++

Renames the cluster.

:directory: cluster-rename

:env. vars: NEW_NAME

:pre-execution: master-node

:post-execution: master-node

OP_CLUSTER_SET_PARAMS

+++++++++++++++++++++

Modifies the cluster parameters.

:directory: cluster-modify

:env. vars: NEW_VG_NAME

:pre-execution: master node

:post-execution: master node

Obsolete operations

~~~~~~~~~~~~~~~~~~~

The following operations are no longer present or don't execute hooks

anymore in Ganeti 2.0:

- OP_INIT_CLUSTER

- OP_MASTER_FAILOVER

- OP_INSTANCE_ADD_MDDRBD

- OP_INSTANCE_REMOVE_MDDRBD

Environment variables

---------------------

Note that all variables listed here are actually prefixed with

*GANETI_* in order to provide a clear namespace.

Common variables

~~~~~~~~~~~~~~~~

This is the list of environment variables supported by all operations:

HOOKS_VERSION

  Documents the hooks interface version. In case this doesnt match

  what the script expects, it should not run. The documents conforms

  to the version 2.

HOOKS_PHASE

  One of *PRE* or *POST* denoting which phase are we in.

CLUSTER

  The cluster name.

MASTER

  The master node.

OP_CODE

  One of the *OP_* values from the list of operations.

OBJECT_TYPE

  One of ``INSTANCE``, ``NODE``, ``CLUSTER``.

DATA_DIR

  The path to the Ganeti configuration directory (to read, for

  example, the *ssconf* files).

Specialised variables

~~~~~~~~~~~~~~~~~~~~~

This is the list of variables which are specific to one or more

operations.

INSTANCE_NAME

  The name of the instance which is the target of the operation.

INSTANCE_DISK_TEMPLATE

  The disk type for the instance.

INSTANCE_DISK_COUNT

  The number of disks for the instance.

INSTANCE_DISKn_SIZE

  The size of disk *n* for the instance.

INSTANCE_DISKn_MODE

  Either *rw* for a read-write disk or *ro* for a read-only one.

INSTANCE_NIC_COUNT

  The number of NICs for the instance.

INSTANCE_NICn_BRIDGE

  The bridge to which the *n* -th NIC of the instance is attached.

INSTANCE_NICn_IP

  The IP (if any) of the *n* -th NIC of the instance.

INSTANCE_NICn_MAC

  The MAC address of the *n* -th NIC of the instance.

INSTANCE_OS_TYPE

  The name of the instance OS.

INSTANCE_PRIMARY

  The name of the node which is the primary for the instance.

INSTANCE_SECONDARIES

  Space-separated list of secondary nodes for the instance.

INSTANCE_MEMORY

  The memory size (in MiBs) of the instance.

INSTANCE_VCPUS

  The number of virtual CPUs for the instance.

INSTANCE_STATUS

  The run status of the instance.

NODE_NAME

  The target node of this operation (not the node on which the hook

  runs).

NODE_PIP

  The primary IP of the target node (the one over which inter-node

  communication is done).

NODE_SIP

  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.

FORCE

  This is provided by some operations when the user gave this flag.

IGNORE_CONSISTENCY

  The user has specified this flag. It is used when failing over

  instances in case the primary node is down.

ADD_MODE

  The mode of the instance create: either *create* for create from

  scratch or *import* for restoring from an exported image.

SRC_NODE, SRC_PATH, SRC_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.

NEW_SECONDARY

  The name of the node on which the new mirror component is being

  added. This can be the name of the current secondary, if the new

  mirror is on the same secondary.

OLD_SECONDARY

  The name of the old secondary in the replace-disks command Note that

  this can be equal to the new secondary if the secondary node hasn't

  actually changed.

EXPORT_NODE

  The node on which the exported image of the instance was done.

EXPORT_DO_SHUTDOWN

  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.

CLUSTER_TAGS

  The list of cluster tags, space separated.

NODE_TAGS_<name>

  The list of tags for node *<name>*, space separated.

Examples

--------

The startup of an instance will pass this environment to the hook

script::

  GANETI_CLUSTER=cluster1.example.com

  GANETI_DATA_DIR=/var/lib/ganeti

  GANETI_FORCE=False

  GANETI_HOOKS_PATH=instance-start

  GANETI_HOOKS_PHASE=post

  GANETI_HOOKS_VERSION=2

  GANETI_INSTANCE_DISK0_MODE=rw

  GANETI_INSTANCE_DISK0_SIZE=128

  GANETI_INSTANCE_DISK_COUNT=1

  GANETI_INSTANCE_DISK_TEMPLATE=drbd

  GANETI_INSTANCE_MEMORY=128

  GANETI_INSTANCE_NAME=instance2.example.com

  GANETI_INSTANCE_NIC0_BRIDGE=xen-br0

  GANETI_INSTANCE_NIC0_IP=

  GANETI_INSTANCE_NIC0_MAC=aa:00:00:a5:91:58

  GANETI_INSTANCE_NIC_COUNT=1

  GANETI_INSTANCE_OS_TYPE=debootstrap

  GANETI_INSTANCE_PRIMARY=node3.example.com

  GANETI_INSTANCE_SECONDARIES=node5.example.com

  GANETI_INSTANCE_STATUS=down

  GANETI_INSTANCE_VCPUS=1

  GANETI_MASTER=node1.example.com

  GANETI_OBJECT_TYPE=INSTANCE

  GANETI_OP_CODE=OP_INSTANCE_STARTUP

  GANETI_OP_TARGET=instance2.example.com