Procedure to migrate an existing MariaDB Galera Cluster from wsrep_ssl_mode=SERVER (encryption only) to SERVER_X509 (encryption plus X.509 verification) with a node-by-node rolling restart.
Most clusters running the default wsrep_ssl_mode=SERVER encrypt replication traffic but do not authenticate peers (see Encryption vs Authentication in Galera Cluster). This guide migrates such a cluster to SERVER_X509, which adds X.509 certificate verification, without a flag day.
wsrep_ssl_mode is read-only and can only be changed at startup, so each node must be restarted to adopt the new mode.
Confirm every node has a certificate signed by the cluster CA. At this stage certificate subjects do not need to match anything — only chain validity is required for SERVER_X509.
Perform a rolling change, one node at a time:
Set wsrep_ssl_mode=SERVER_X509 in the [mariadb] section of the node's configuration file.
Restart the node.
Confirm the node rejoins the cluster and reaches the Synced state before continuing.
Repeat for each remaining node.
Once every node has been restarted with SERVER_X509, the cluster verifies certificate chains on every inter-node connection.
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