MySQL Router  /  General Information  /  Routing for MySQL InnoDB cluster

1.1 Routing for MySQL InnoDB cluster

MySQL Router is part of InnoDB cluster, and is lightweight middleware that provides transparent routing between your application and back-end MySQL Servers. It can be used for a wide variety of use cases, such as providing high availability and scalability by effectively routing database traffic to appropriate back-end MySQL Servers. The pluggable architecture also enables developers to extend MySQL Router for custom use cases.

For additional details about how Router is part of InnoDB cluster, see InnoDB Cluster.

Introduction

For client applications to handle failover, they need to be aware of the InnoDB cluster topology and know which MySQL instance is the PRIMARY. While it is possible for applications to implement that logic, MySQL Router can provide and handle this functionality for you.

MySQL uses Group Replication to replicate databases across multiple servers while performing automatic failover in the event of a server failure. When used with a MySQL InnoDB cluster, MySQL Router acts as a proxy to hide the multiple MySQL instances on your network and map the data requests to one of the instances in the cluster. As long as there are enough online replicas, and communication between the components is intact, applications will be able to contact one of them. Router also makes it possible for this to happen by simply repointing applications to connect to Router instead of directly to MySQL.

Deploying Router with MySQL InnoDB cluster

The recommended deployment model for MySQL Router is with InnoDB cluster, with Router sitting on the same host as the application.

The steps for deploying Router with an InnoDB cluster after the cluster is configured are:

  1. Install MySQL Router.

    For details, see the Installation section.

  2. Bootstrap for an InnoDB cluster, and test.

    Router can be automatically configured by calling it with --bootstrap. During bootstrap, Router connects to the cluster, fetches its metadata, and configures itself for use. For details, see Chapter 3, Deploying MySQL Router.

  3. Set up Router for automatic startup.

    To make Router automatically start when the host reboots, you need to configure your system to start Router. This process is similar to how the MySQL server is configured to start automatically. For additional details, see Section 5.1, “Starting MySQL Router”.

For example, after creating a MySQL InnoDB cluster, you might configure Router using:

shell> mysqlrouter --bootstrap localhost:3310 --directory /opt/myrouter --user snoopy

This example bootstraps MySQL Router to an existing InnoDB cluster where:

  • localhost:3310 is the PRIMARY with a metadata server

  • Creates a self-contained installation with all generated directories and files at /opt/myrouter/

  • Only the host's system user named snoopy will have access to /opt/myrouter/*

  • Files and directories are generated under /opt/myrouter/ including start.sh, stop.sh, log/, and a fully functional MySQL Router configuration file named mysqlrouter.conf.

See the --bootstrap and related configuration options for information to modify how the bootstrap process is configured. For example, passing in --conf-use-sockets enables Unix domain socket connections because only TCP/IP connections are enabled by default.

Bootstrapping and group_replication_single_primary_mode

When bootstrapping, the available ports and sockets are affected by the group_replication_single_primary_mode MySQL server configuration option.

Note

This document refers to default bootstrapping behavior. Other MySQL Router configuration options may affect this behavior, and generated configuration values can be modified after bootstrapping.

  • With group_replication_single_primary_mode=ON (the default): Both Read-Write (primary) and Read-Only (secondary) ports are configured.

  • With group_replication_single_primary_mode=OFF: Only Read-Write (primary) ports are configured.

For example:

With group_replication_single_primary_mode=ON, all connections to ports 6446 and 64460 go to the single primary, and all connections to ports 6447 and 64470 go to the secondaries using the round-robin mode schedule.

shell> mysqlrouter --bootstrap localhost:3310

Classic MySQL protocol connections to cluster 'myCluster':
- Read/Write Connections: localhost:6446
- Read/Only Connections: localhost:6447

X protocol connections to cluster 'myCluster':
- Read/Write Connections: localhost:64460
- Read/Only Connections: localhost:64470

With group_replication_single_primary_mode=OFF, all connections to ports 6446 and 64460 go to the primaries using the round-robin mode schedule.

shell> mysqlrouter --bootstrap localhost:3310

Classic MySQL protocol connections to cluster 'myCluster':
- Read/Write Connections: localhost:6446

X protocol connections to cluster 'myCluster':
- Read/Write Connections: localhost:64460

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