7.8.1 Rejoining an Instance to a Cluster

If an instance leaves the cluster, for example because it lost connection, and for some reason it could not automatically rejoin the cluster, it might be necessary to rejoin it to the cluster at a later stage. To rejoin an instance to a cluster issue Cluster.rejoinInstance(instance).

Tip

If the instance has super_read_only=ON then you might need to confirm that AdminAPI can set super_read_only=OFF. See Instance Configuration in Super Read-only Mode for more information.

In the case where an instance has not had its configuration persisted (see Section 6.2.3, “Persisting Settings”), upon restart the instance does not rejoin the cluster automatically. The solution is to issue cluster.rejoinInstance() so that the instance is added to the cluster again and ensure the changes are persisted. Once the InnoDB Cluster configuration is persisted to the instance's option file it rejoins the cluster automatically.

If you are rejoining an instance which has changed in some way then you might have to modify the instance to make the rejoin process work correctly. For example, when you restore a MySQL Enterprise Backup backup, the server_uuid changes. Attempting to rejoin such an instance fails because InnoDB Cluster instances are identified by the server_uuid variable. In such a situation, information about the instance's old server_uuid must be removed from the InnoDB Cluster metadata and then a Cluster.rescan() must be executed to add the instance to the metadata using it's new server_uuid. For example:

cluster.removeInstance("root@instanceWithOldUUID:3306", {force: true})

cluster.rescan()

In this case you must pass the force option to the Cluster.removeInstance() method because the instance is unreachable from the cluster's perspective and we want to remove it from the InnoDB Cluster metadata anyway.

rejoinInstance() also checks the communication stack used by the instance and ensures it is supported by the cluster. If the cluster supports the communication stack, rejoinInstance() adds the instance to the cluster.