- the :command:`ganeti-masterd` daemon which runs on the master node and
allows control of the cluster
+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
+
+
Instance
~~~~~~~~
internall 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.
+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
passing the disk information you specify the current volumes::
gnt-instance add -t plain -n HOME_NODE ... \
- --disk 0:adopt=lv_name INSTANCE_NAME
+ --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
# later convert it to redundant
gnt-instance stop INSTANCE
- gnt-instance modify -t drbd INSTANCE
+ gnt-instance modify -t drbd -n NEW_SECONDARY INSTANCE
gnt-instance start INSTANCE
# and convert it back
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 masterfailover
+ 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
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 ``.+*/:-``.
+comprised by alphanumeric characters and additionally ``.+*/:@-``.
Operations
++++++++++
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 xen-devi-18.fra.corp.google.com on node mpgntac4.fra.corp.google.com
+ 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...
node1#
top-level queue directory, or look at its contents (it's a
JSON-formatted file).
+Special Ganeti deployments
+--------------------------
+
+Since Ganeti 2.4, it is possible to extend the Ganeti deployment with
+two custom scenarios: Ganeti inside Ganeti and multi-site model.
+
+Running Ganeti under Ganeti
++++++++++++++++++++++++++++
+
+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``::
+
+ node1# gnt-node modify --vm-capable=no node3
+
+The vm_capable status can be listed as usual via ``gnt-node list``::
+
+ node1# 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.
+
+Multi-site model
+++++++++++++++++
+
+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::
+
+ node1# 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::
+
+ node1# 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).
+
+
Ganeti tools
------------
recreated from it and if the instance disks have not been lost it
permits recovery from the loss of all master candidates.
+move-instance
++++++++++++++
+
+See :doc:`separate documentation for move-instance <move-instance>`.
+
+.. TODO: document cluster-merge tool
+
Other Ganeti projects
---------------------
projects / ganeti-local / blobdiff