Using Redis with WordPress

There are a number of Redis plugins for WordPress, only some of which are compatible with Platform.sh. We’ve tested and recommend WP Redis and Redis Object Cache, both of which require a minimal amount of configuration.

Requirements

1. Add a Redis service

To create a Redis service, add the following to your services configuration:

rediscache:
  type: redis:6.0

That creates a service named rediscache with the type redis, specifically version 6.0.

2. Expose the Redis service to your application

Next open a connection to the new Redis service. In the relationships section of your app configuration, add the following:

relationships:
  redis: "rediscache:redis"

The key (left side) is the name that’s exposed to the application in the PLATFORM_RELATIONSHIPS variable. The value (right side) is the name of the service you specified in step 1 (rediscache) and the endpoint (redis). If you named the service something different in step 1, change rediscache to that.

3. Add the Redis PHP extension

Add the Redis extension for PHP in one of two ways:

• In your app configuration (for extension versions tied to the PHP version)
• Using a builder script (if you need more control over the extension version)

4. Add the Redis library

If you’re using Composer to build WordPress, install your chosen Redis plugin with a Composer command depending on the plugin:

composer require "wpackagist-plugin/wp-redis":"^1.1.4"

composer require "wpackagist-plugin/redis-cache":"^2.0.23"

Then commit the resulting changes to your composer.json and composer.lock files.

Configuration

To enable the Redis cache to work with WordPress, the object-cache.php file needs to be copied from the plugin’s directory to the wp-content directory. Add the following line to the bottom of your build hook in your app configuration, adjusting the paths based on where your plugins are located:

hooks:
  build: |
    ...
    if [ -f wordpress/wp-content/plugins/wp-redis/object-cache.php ]; then
        cp wordpress/wp-content/plugins/wp-redis/object-cache.php wordpress/wp-content/object-cache.php
    fi    

hooks:
  build: |
    ...
    if [ -f wordpress/wp-content/plugins/redis-cache/includes/object-cache.php ]; then
        cp wordpress/wp-content/plugins/redis-cache/includes/object-cache.php wordpress/wp-content/object-cache.php
    fi    

It should now look something like:

hooks:
  build: |
    set -e
    bash .platform-scripts/install-redis.sh 6.0.12
    # Copy manually-provided plugins into the plugins directory.
    # This allows manually-provided and composer-provided plugins to coexist.
    rsync -a plugins/* wordpress/wp-content/plugins/

    if [ -f wordpress/wp-content/plugins/redis-cache/includes/object-cache.php ]; then
      cp wordpress/wp-content/plugins/redis-cache/includes/object-cache.php wordpress/wp-content/object-cache.php
    fi    

Each plugin requires slightly different configuration. Place the code for your chosen plugin in the wp-config.php file, somewhere before the final require_once(ABSPATH . 'wp-settings.php'); line.

<?php

if ($config->hasRelationship('redis') && extension_loaded('redis')) {
    $credentials = $config->credentials('redis');
    $redis_server = array(
        'host'     => $credentials['host'],
        'port'     => $credentials['port'],
        'auth'     => $credentials['password'],
    );
}

<?php

if ($config->hasRelationship('redis') && extension_loaded('redis')) {
    $credentials = $config->credentials('redis');

    define('WP_REDIS_CLIENT', 'phpredis');
    define('WP_REDIS_HOST', $credentials['host']);
    define('WP_REDIS_PORT', $credentials['port']);
}

These sections set up the parameters the plugins look for to connect to the Redis server. If you used a different name for the relationship above, change it accordingly. This code has no impact when run on a local development environment.

Once you have committed the above changes and pushed, you need to activate the plugins.

Verifying Redis is running

Run this command in a SSH session in your environment: platform redis info. You should run it before you push all this new code to your repository.

This should give you a baseline of activity on your Redis installation. There should be very little memory allocated to the Redis cache.

After you push this code, you should run the command and notice that allocated memory starts jumping.

To verify the plugins are working, add a redis command to the WP CLI tool. While in a SSH session in your environment, you can run wp help redis to see the available commands your chosen plugin has added.