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MySQL 5.7 Reference Manual  /  InnoDB Cluster  /  Using MySQL Router with InnoDB Cluster

20.3 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.

Note

Do not attempt to configure MySQL Router manually to redirect to the ports of an InnoDB cluster. Always use the --bootstrap option as this ensures that MySQL Router takes its configuration from the InnoDB cluster's metadata. See Cluster Metadata and State.

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. You need the MASTER key of the InnoDB cluster to auto-configure MySQL Router.

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 type 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 creates a configuration 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
Tip

When you change the topology of a cluster by adding another server instance after you have bootstrapped MySQL Router, you need to update bootstrap_server_addresses based on the updated metadata. Either restart MySQL Router using the --bootstrap option, or manually edit the bootstrap_server_addresses section of the mysqlrouter.conf file and restart MySQL Router.

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 Section 19.3, “Setting Up MySQL as a Document Store”. The default available TCP ports are:

  • 6446 - for Classic MySQL protocol read-write sessions, which MySQL Router redirects incoming connections to primary server instances.

  • 6447 - for Classic MySQL protocol read-only sessions, which MySQL Router redirects incoming connections to one of the secondary server instances.

  • 64460 - for X Protocol read-write sessions, which MySQL Router redirects incoming connections to primary server instances.

  • 64470 - for X Protocol read-only sessions, which MySQL Router redirects incoming connections to one of the secondary server instances.

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, read-write sessions are redirected to the single primary, with a multi-primary cluster read-write sessions are redirected to one of the primary instances. For incoming read-only connections MySQL Router redirects connections to one of the secondary instances in a round-robin fashion.

Once bootstrapped and configured, start MySQL Router:

shell> mysqlrouter &

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 |
+--------+

Testing High Availability

To test if high availability works, simulate an unexpected halt by killing an instance. The cluster detects the fact that the instance left the cluster and reconfigures itself. Exactly how the cluster reconfigures itself depends on whether you are using a single-primary or multi-primary cluster, and the role the instance serves within the cluster.

In single-primary mode:

  • If the current primary leaves the cluster, one of the secondary instances is elected as the new primary, with instances prioritized by the lowest server_uuid. MySQL Router redirects read-write connections to the newly elected primary.

  • If a current secondary leaves the cluster, MySQL Router stops redirecting read-only connections to the instance.

For more information see Section 17.4.1.1, “Single-Primary Mode”.

In multi-primary mode:

  • If a current "R/W" instance leaves the cluster, MySQL Router redirects read-write connections to other primaries.

  • If a current "R/O" instance leaves the cluster,

For more information see Section 17.4.1.2, “Multi-Primary Mode”.

There are various ways to simulate an instance leaving a cluster, for example you can forcibly stop the MySQL server on an instance, or use the AdminAPI dba.killSandboxInstance() if testing a sandbox deployment. In this example assume there is a single-primary sandbox cluster deployment with three server instances and the instance listening at port 3310 is the current primary. Simulate the instance leaving the cluster unexpectedly:

mysql-js> dba.killSandboxInstance(3310)

Switch to SQL mode in MySQL Shell using the \sql command and verify the port variable to check which instance you are connected to. Notice that the first SELECT statement fails as the connection to the original primary was lost. This means the current session has been closed, MySQL Shell automatically reconnects for you and when you issue the command again the new port is confirmed.

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)

This shows that the InnoDB cluster provided us with automatic failover, that MySQL Router has automatically reconnected us to the new primary instance, and that we have high availability.

MySQL Router and Metadata Servers

When MySQL Router is bootstrapped against a cluster, it records the server instance's addresses in its configuration file. If any additional instances are added to the cluster after bootstrapping the MySQL Router, they are not automatically detected and therefore are not used for connection routing.

To ensure that newly added instances are routed to correctly you must bootstrap MySQL Router against the cluster to read the updated metadata. This means that you must restart MySQL Router and include the --bootstrap option.


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