Define preferred SST donor for Galera Cluster

One of our customers recently ran into a problem, where he wanted to have a preferred donor for SST, whenever a node came up. The problem was, that the node did not come up, when the preferred donor was not running.

In the documentation, you can find the parameter wsrep_sst_donor, which prefers the specified node as SST donor. This is great, as long as the donor is actually running.

The problem can be fixed by adding a comma to the end of the value of wsrep_sst_donor, what would look like this:

wsrep_sst_donor="galera2,"

Note the comma at the end of the value. This trailing comma basically tells this node, that galera2 is the preferred donor, if galera2 is not available, any other available node will be used as donor.

You could also specify a secondary node, which is needed to be available for the node to come up:

wsrep_sst_donor="galera2,galera1"

In this case, galera1 wil be used as secondary donor if galera2 is not available. If both are not available, the node will refuse to come up.