21.3 Using MySQL Router with InnoDB Cluster

This section describes how to use MySQL Router with InnoDB cluster to achieve high availability. Regardless of whether you have deployed a sandbox or production cluster, MySQL Router can configure itself based on the InnoDB cluster's metadata using the --bootstrap option. This configures MySQL Router automatically to route connections to the cluster's server instances. Client applications connect to the ports MySQL Router provides, without any need to be aware of the InnoDB cluster topology. In the event of a unexpected failure, the InnoDB cluster adjusts itself automatically and MySQL Router detects the change. This removes the need for your client application to handle failover. For more information, see Routing for MySQL InnoDB cluster.

The recommended deployment of MySQL Router is on the same host as the application. When using a sandbox deployment, everything is running on a single host, therefore you deploy MySQL Router to the same host. When using a production deployment, we recommend deploying one MySQL Router instance to each machine used to host one of your client applications. It is also possible to deploy MySQL Router to a common machine through which your application instances connect.

Assuming MySQL Router is already installed (see Installing MySQL Router), use the --bootstrap option to provide the location of a server instance that belongs to the InnoDB cluster. MySQL Router uses the included metadata cache plugin to retrieve the InnoDB cluster's metadata, consisting of a list of server instance addresses which make up the InnoDB cluster and their role in the cluster. You pass the URI-like connection string of the server that MySQL Router should retrieve the InnoDB cluster metadata from. For example:

shell> mysqlrouter --bootstrap ic@ic-1:3306 --user=mysqlrouter

You are prompted for the instance password and encryption key for MySQL Router to use. This encryption key is used to encrypt the instance password used by MySQL Router to connect to the cluster. The ports you can use to connect to the InnoDB cluster are also displayed. The MySQL Router bootstrap process creates a mysqlrouter.conf file, with the settings based on the cluster metadata retrieved from the address passed to the --bootstrap option, in the above example ic@ic-1:3306. Based on the InnoDB cluster metadata retrieved, MySQL Router automatically configures the mysqlrouter.conf file, including a metadata_cache section with bootstrap_server_addresses containing the addresses for all server instances in the cluster. For example:

[metadata_cache:prodCluster]
router_id=1
bootstrap_server_addresses=mysql://ic@ic-1:3306,mysql://ic@ic-2:3306,mysql://ic@ic-3:3306
user=mysql_router1_jy95yozko3k2
metadata_cluster=prodCluster
ttl=300

The generated MySQL Router configuration creates TCP ports which you use to connect to the cluster. Ports for communicating with the cluster using both Classic MySQL protocol and X Protocol are created. To use X Protocol the server instances must have X Plugin installed and configured. For a sandbox deployment, instances have X Plugin set up automatically. For a production deployment, if you want to use X Protocol you need to install and configure X Plugin on each instance, see Setting Up MySQL as a Document Store. The default available TCP ports are:

Depending on your MySQL Router configuration the port numbers might be different to the above. For example if you use the --conf-base-port option, or the group_replication_single_primary_mode variable. The exact ports are listed when you start MySQL Router.

The way incoming connections are redirected depends on the type of cluster being used. When using a single-primary cluster, by default MySQL Router publishes a X Protocol and a classic protocol port, which clients connect to for read-write sessions and which are redirected to the cluster's single primary. With a multi-primary cluster read-write sessions are redirected to one of the primary instances in a round-robin fashion. For example, this means that the first connection to port 6446 would be redirected to the ic-1 instance, the second connection to port 6446 would be redirected to the ic-2 instance, and so on. For incoming read-only connections MySQL Router redirects connections to one of the secondary instances, also in a round-robin fashion. To modify this behavior see the routing_strategy option.

Once bootstrapped and configured, start MySQL Router. If you used a system wide install with the --bootstrap option then issue:

shell> mysqlrouter &

If you installed MySQL Router to a directory using the --directory option, use the start.sh script found in the directory you installed to. Alternatively set up a service to start MySQL Router automatically when the system boots, see Starting MySQL Router. You can now connect a MySQL client, such as MySQL Shell to one of the incoming MySQL Router ports as described above and see how the client gets transparently connected to one of the InnoDB cluster instances.

shell> mysqlsh --uri root@localhost:6442

To verify which instance you are actually connected to, simply issue an SQL query against the port status variable.

mysql-js> \sql
Switching to SQL mode... Commands end with ;
mysql-sql> select @@port;
+--------+
| @@port |
+--------+
|   3310 |
+--------+

mysql-js> dba.killSandboxInstance(3310)

mysql-js> \sql
Switching to SQL mode... Commands end with ;
mysql-sql> SELECT @@port;
ERROR: 2013 (HY000): Lost connection to MySQL server during query
The global session got disconnected.
Attempting to reconnect to 'root@localhost:6446'...
The global session was successfully reconnected.
mysql-sql> SELECT @@port;
+--------+
| @@port |
+--------+
|   3330 |
+--------+
1 row in set (0.00 sec)