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# Merging clusters

With `cluster-merge` from the `tools` directory it is possible to merge two or more clusters into one single cluster.

If anything goes wrong at any point the script suggests you rollback steps you’ve to perform manually if there are any. The point of no return is when the master daemon is started the first time after merging the configuration files. A rollback at this point would involve a lot of manual work.

For the internal design of this tool have a look at the Automated Ganeti Cluster Merger <design-2.1.rst> document.

## Merge Clusters

The tool has to be invoked on the cluster you like to merge the other clusters into.

The usage of `cluster-merge` is as follows:

    cluster-merge [--debug|--verbose] [--watcher-pause-period SECONDS] \
    [--groups [merge|rename]] <cluster> [<cluster...>]

You can provide multiple clusters. The tool will then go over every cluster in serial and perform the steps to merge it into the invoking cluster.

These options can be used to control the behaviour of the tool:

`--debug`/`--verbose`
  These options are mutually exclusive and increase the level of output to either debug output or just more verbose output like action performed right now.
`--watcher-pause-period`
  Define the period of time in seconds the watcher shall be disabled, default is 1800 seconds (30 minutes).
`--groups`
  This option controls how `cluster-merge` handles duplicate node group names on the merging clusters. If `merge` is specified then all node groups with the same name will be merged into one. If `rename` is specified, then conflicting node groups on the remove clusters will have their cluster name appended to the group name. If this option is not speicifed, then `cluster-merge` will refuse to continue if it finds conflicting group names, otherwise it will proceed as normal.

## Rollback

If for any reason something in the merge doesn’t work the way it should `cluster-merge` will abort, provide an error message and optionally rollback steps. Please be aware that after a certain point there’s no easy way to rollback the cluster to its previous state. If you’ve reached that point the tool will not provide any rollback steps.

If you end up with rollback steps, please perform them before invoking the tool again. It doesn’t keep state over invokations.

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