MySQL InnoDB Cluster provides a complete high availability solution for MySQL. By using AdminAPI, which is included with MySQL Shell, you can easily configure and administer a group of at least three MySQL server instances to function as an InnoDB Cluster.

Each MySQL server instance in an InnoDB Cluster runs MySQL Group Replication, which provides the mechanism to replicate data within an InnoDB Cluster, with built-in failover. AdminAPI removes the need to work directly with Group Replication in an InnoDB Cluster, but for more information see Group Replication which explains the details. From MySQL 8.0.27, you can also set up InnoDB ClusterSet (see Chapter 8, MySQL InnoDB ClusterSet) to provide disaster tolerance for InnoDB Cluster deployments by linking a primary InnoDB Cluster with one or more replicas of itself in alternate locations, such as different datacenters.

MySQL Router can automatically configure itself based on the cluster you deploy, connecting client applications transparently to the server instances. In the event of an unexpected failure of a server instance the cluster reconfigures automatically. In the default single-primary mode, an InnoDB Cluster has a single read-write server instance - the primary. Multiple secondary server instances are replicas of the primary. If the primary fails, a secondary is automatically promoted to the role of primary. MySQL Router detects this and forwards client applications to the new primary. Advanced users can also configure a cluster to have multiple primaries.

The following diagram shows an overview of how the technologies work together:

Figure 7.1 InnoDB Cluster overview

Three MySQL servers are grouped together as a high availability cluster. One of the servers is the read/write primary instance, and the other two are read-only secondary instances. Group Replication is used to replicate data from the primary instance to the secondary instances. MySQL Router connects client applications (in this example, a MySQL Connector) to the primary instance.

Important

InnoDB Cluster does not provide support for MySQL NDB Cluster. NDB Cluster depends on the NDB storage engine as well as a number of programs specific to NDB Cluster which are not furnished with MySQL Server 8.0; NDB is available only as part of the MySQL NDB Cluster distribution. In addition, the MySQL server binary (mysqld) that is supplied with MySQL Server 8.0 cannot be used with NDB Cluster. For more information about MySQL NDB Cluster, see MySQL NDB Cluster 8.0. MySQL Server Using InnoDB Compared with NDB Cluster, provides information about the differences between the InnoDB and NDB storage engines.

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