Use Redis cache with Bedrock and Trellis

bedrock
9

Many thanks for sharing your insights + setups @strarsis & @Simeon, much appreciated…!

I went ahead and got Redis to work, a few thoughts / additions regarding the setup:

The forked Ansible role https://github.com/im-mortal/trellis-redis was a great starting point for me but there were a few things I needed to add / tweak so I forked that one as https://github.com/E-VANCE/trellis-redis.

  • The version-specific PHP package is missing, thus I couldn’t get Redis to work. Added this to /tasks/main.yml 
- name: Install php-redis (version specific)
  apt:
    pkg: php7.4-redis
    state: present
    update_cache: true
  notify: Restart php-fpm

NOTE: Could / should use a version-placeholder for upwards compatibility…

  • The default Redis-config only assigned 128mb as redis_maxmemory (which might be sensible, not sure as of now) but also set redis_maxmemory_policy to noeviction which makes Redis return a write error once the memory limit has been reached… Thus:
# Max memory values
redis_maxmemory: 2gb
redis_maxmemory_policy: volatile-ttl
redis_maxmemory_samples: 5

NOTE: See this great article regarding the memory aspects as well as the ansible-redis readme which has extensive explanations on the config variables / parameters

  • Setting the WP_REDIS_DEFAULT_EXPIRE_SECONDS constant via Bedrock’s config/application.php allows for a sensible key expiration, see #263 in WP Redis
  • Monitor the memory usage and check for plugins that put a great load on Redis, those can be excluded via the designated wp_cache_add_non_persistent_groups-function in WP Redis
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