20.1 Introducing InnoDB Cluster

MySQL InnoDB cluster provides a complete high availability solution for MySQL. MySQL Shell includes AdminAPI which enables you to easily configure and administer a group of at least three MySQL server instances to function as an InnoDB cluster. Each MySQL server instance runs MySQL Group Replication, which provides the mechanism to replicate data within InnoDB clusters, with built-in failover. AdminAPI removes the need to work directly with Group Replication in InnoDB clusters, but for more information see Chapter 17, Group Replication which explains the details. 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.


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 5.7; 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 5.7 cannot be used with NDB Cluster. For more information about MySQL NDB Cluster, see Chapter 21, MySQL NDB Cluster 7.5 and NDB Cluster 7.6. Section 21.1.6, “MySQL Server Using InnoDB Compared with NDB Cluster”, provides information about the differences between the InnoDB and NDB storage engines.

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

Figure 20.1 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. The cluster admin capability in MySQL Shell can connect directly to the primary instance using the MySQL X AdminAPI, or it can connect through MySQL Router like other client applications.

Using AdminAPI

MySQL Shell includes the AdminAPI, which is accessed through the dba global variable and its associated methods. The dba variable's methods enable you to deploy, configure, and administer InnoDB clusters. For example, use the dba.createCluster() method to create an InnoDB cluster.


MySQL Shell enables you to connect to servers over a socket connection, but AdminAPI requires TCP connections to a server instance. Do not use socket based connections with AdminAPI.

MySQL Shell provides online help for the AdminAPI. To list all available dba commands, use the dba.help() method. For online help on a specific method, use the general format object.help('methodname'). For example:

mysql-js> dba.help('getCluster')

Retrieves a cluster from the Metadata Store.


  name: Parameter to specify the name of the cluster to be returned.


If name is not specified, the default cluster will be returned.

If name is specified, and no cluster with the indicated name is found, an error
will be raised.