Using Memcached with Drupal 9.x

Platform.sh recommends using Redis for caching with Drupal over Memcached, as Redis offers better performance when dealing with larger values as Drupal tends to produce. But Memcached is also available if desired and is fully supported.

Requirements 

Add a Memcached service 

1. Configure the service 

Use the memcached type to define the service:

.platform/services.yaml
<SERVICE_NAME>:
    type: memcached:<VERSION>

Note that if you later change the name, it’s treated as an entirely new service. This removes all data from your service. Always backup your data before changing the service.

2. Add the relationship 

Use the memcached endpoint to define the relationship:

.platform.app.yaml
relationships:
    <RELATIONSHIP_NAME>: "<SERVICE_NAME>:memcached"

You can define <SERVICE_NAME> and <RELATIONSHIP_NAME> as you like, but it’s best if they’re distinct.

For PHP, enable the extension for the service:

.platform.app.yaml
runtime:
    extensions:
        - memcached

Example Configuration 

Service definition

.platform/services.yaml
cachemc:
    type: memcached:1.6

App configuration

.platform.app.yaml
relationships:
    memcachedcache: "cachemc:memcached"

runtime:
    extensions:
        - memcached

Add the Drupal module 

You need to add the Memcache module to your project. If you’re using Composer to manage your Drupal site (which is recommended), run:

composer require drupal/memcache

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

Configuration 

The Drupal Memcache module must be configured via settings.platformsh.php.

Place the following at the end of settings.platformsh.php. Note the inline comments, as you may wish to customize it further. Also review the README.txt file that comes with the Memcache module, as it has a more information on possible configuration options. For instance, you may want to consider using Memcache for locking as well as configuring cache stampede protection.

The example below is intended as a “most common case” and has been tested with version 8.x-2.3 of the Memcache module.

<?php

// If you named your Memcached relationship something other than "memcachedcache", set that here.
$relationship_name = 'memcachedcache';

if ($platformsh->hasRelationship($relationship_name) && extension_loaded('memcached')) {
  $platformsh->registerFormatter('drupal-memcached', function($creds) {
    return sprintf("%s:%d", $creds['host'], $creds['port']);
  });

  // This is the line that tells Drupal to use Memcached as a backend.
  // Comment out just this line if you need to disable it for some reason and
  // fall back to the default database cache.
  $settings['cache']['default'] = 'cache.backend.memcache';

  $host = $platformsh->formattedCredentials($relationship_name, 'drupal-memcached');
  $settings['memcache']['servers'][$host] = 'default';

  // By default Drupal starts the cache_container on the database. The following
  // code overrides that.
  // Make sure that the $class_load->addPsr4 is pointing to the right location of
  // the Memcache module. The value below should be correct if Memcache was installed
  // using Drupal Composer.
  $memcache_exists = class_exists('Memcache', FALSE);
  $memcached_exists = class_exists('Memcached', FALSE);
  if ($memcache_exists || $memcached_exists) {
    $class_loader->addPsr4('Drupal\\memcache\\', 'modules/contrib/memcache/src');

    // If using a multisite configuration, adapt this line to include a site-unique
    // value.
    $settings['memcache']['key_prefix'] = $platformsh->environment;

    // Define custom bootstrap container definition to use Memcache for cache.container.
    $settings['bootstrap_container_definition'] = [
      'parameters' => [],
      'services' => [
        'database' => [
          'class' => 'Drupal\Core\Database\Connection',
          'factory' => 'Drupal\Core\Database\Database::getConnection',
          'arguments' => ['default'],
        ],
        'settings' => [
          'class' => 'Drupal\Core\Site\Settings',
          'factory' => 'Drupal\Core\Site\Settings::getInstance',
        ],
        'memcache.settings' => [
          'class' => 'Drupal\memcache\MemcacheSettings',
          'arguments' => ['@settings'],
        ],
        'memcache.factory' => [
          'class' => 'Drupal\memcache\Driver\MemcacheDriverFactory',
          'arguments' => ['@memcache.settings'],
        ],
        'memcache.timestamp.invalidator.bin' => [
          'class' => 'Drupal\memcache\Invalidator\MemcacheTimestampInvalidator',
          # Adjust tolerance factor as appropriate when not running memcache on localhost.
          'arguments' => ['@memcache.factory', 'memcache_bin_timestamps', 0.001],
        ],
        'memcache.backend.cache.container' => [
          'class' => 'Drupal\memcache\DrupalMemcacheInterface',
          'factory' => ['@memcache.factory', 'get'],
          'arguments' => ['container'],
        ],
        'lock.container' => [
          'class' => 'Drupal\memcache\Lock\MemcacheLockBackend',
          'arguments' => ['container', '@memcache.backend.cache.container'],
        ],
        'cache_tags_provider.container' => [
          'class' => 'Drupal\Core\Cache\DatabaseCacheTagsChecksum',
          'arguments' => ['@database'],
        ],
        'cache.container' => [
          'class' => 'Drupal\memcache\MemcacheBackend',
          'arguments' => ['container', '@memcache.backend.cache.container','@cache_tags_provider.container','@memcache.timestamp.invalidator.bin'],
        ],
      ],
    ];
  }
}