Switching to a new master (or new primary if to use the new naming) in a MySQL 8 InnoDB Cluster is simple with the MySQL Shell console and the function of the cluster variable – setPrimaryInstance.
Why would someone need to do it manually? One of the reasons may be because one of the nodes is on the same physical server and thus suppose a smaller latency.
First, get a cluster object of the cluster by connecting to the cluster API with MySQL Shell:
[root@db-cluster-1 ~]# mysqlsh MySQL Shell 8.0.28 Copyright (c) 2016, 2022, Oracle and/or its affiliates. Oracle is a registered trademark of Oracle Corporation and/or its affiliates. Other names may be trademarks of their respective owners. Type '\help' or '\?' for help; '\quit' to exit. MySQL JS > \connect clusteradmin@db-cluster-1 Creating a session to 'clusteradmin@db-cluster-1' Fetching schema names for autocompletion... Press ^C to stop. Your MySQL connection id is 166928419 (X protocol) Server version: 8.0.28 MySQL Community Server - GPL No default schema selected; type \use <schema> to set one. MySQL db-cluster-1:33060+ ssl JS > var cluster = dba.getCluster()
Second, show the status of the cluster to get the cluster topology and the exact nodes’ names, which will use as an argument of the setPrimaryInstance. Still, in the MySQL Shell Console:
MySQL db-cluster-1:33060+ ssl JS > cluster.status()
{
"clusterName": "mycluster1",
"defaultReplicaSet": {
"name": "default",
"primary": "db-cluster-2:3306",
"ssl": "REQUIRED",
"status": "OK",
"statusText": "Cluster is ONLINE and can tolerate up to ONE failure.",
"topology": {
"db-cluster-1:3306": {
"address": "db-cluster-1:3306",
"memberRole": "SECONDARY",
"mode": "R/O",
"readReplicas": {},
"replicationLag": null,
"role": "HA",
"status": "ONLINE",
"version": "8.0.28"
},
"db-cluster-2:3306": {
"address": "db-cluster-2:3306",
"memberRole": "PRIMARY",
"mode": "R/W",
"readReplicas": {},
"replicationLag": null,
"role": "HA",
"status": "ONLINE",
"version": "8.0.28"
},
"db-cluster-3:3306": {
"address": "db-cluster-3:3306",
"memberRole": "SECONDARY",
"mode": "R/O",
"readReplicas": {},
"replicationLag": null,
"role": "HA",
"status": "ONLINE",
"version": "8.0.28"
}
},
"topologyMode": "Single-Primary"
},
"groupInformationSourceMember": "db-cluster-2:3306"
}