Redis Object Caching for WordPress in Trellis

Trellis supports two types of caching that work together:

• FastCGI Cache - Full page caching at the nginx level
• Object Cache - Database query and transient caching (Redis or Memcached)

These can be used independently or together for optimal performance.

Configuration #

Maximum Performance (FastCGI + Object Cache) #

Enable both FastCGI page caching and Redis object caching:

wordpress_sites:
  example.com:
    cache:
      enabled: true # Enables FastCGI page caching
      duration: 30s # FastCGI cache duration
    object_cache:
      enabled: true # Enables object caching
      provider: redis # Use Redis (or memcached)
      database: 0 # Redis database number

FastCGI Cache Only (Default/Backward Compatible) #

Existing configurations continue to work unchanged:

cache:
  enabled: true # FastCGI page caching only
  duration: 30s
  skip_cache_uri: /wp-admin/|/wp-json/|/xmlrpc.php
  skip_cache_cookie: comment_author|wordpress_[a-f0-9]+
  background_update: "on"

Object Cache Only #

If you need Redis object cache without page caching:

cache:
  enabled: false # Disable FastCGI page caching
object_cache:
  enabled: true # Enable object caching
  provider: redis # Use Redis (or memcached)
  database: 0 # Redis database number

Cache Types #

FastCGI Cache (Page Caching) #

• Purpose: Caches complete HTML pages
• Performance: Fastest possible page loads for cached content
• Best for: High-traffic sites with mostly static content
• Location: nginx level, bypasses PHP entirely

Redis Object Cache #

• Purpose: Caches database queries, transients, and objects
• Performance: Reduces database load significantly
• Best for: Database-heavy sites, complex queries
• Features: Persistent across page loads, shared data

Memcached Object Cache #

• Purpose: Alternative to Redis for object caching
• Performance: Similar to Redis, slightly different characteristics
• Best for: When Redis isn't available or preferred

WordPress Plugin Installation #

For Redis Object Cache #

Install a Redis object cache plugin in your WordPress site:

1. Redis Object Cache (recommended): https://wordpress.org/plugins/redis-cache/

composer require wpackagist-plugin/redis-cache

2. After deployment, activate the plugin and enable object caching:

wp plugin activate redis-cache
wp redis enable

For Memcached Object Cache #

Install a Memcached object cache plugin:

1. Memcached Object Cache: https://wordpress.org/plugins/memcached/

composer require wpackagist-plugin/memcached

2. The plugin typically auto-activates when it detects Memcached is available.

Configuration Examples #

Maximum Performance Setup #

wordpress_sites:
  example.com:
    cache:
      enabled: true # FastCGI page caching
      duration: 60s
    object_cache:
      enabled: true # Object caching
      provider: redis # Using Redis
      database: 0

Multiple Sites with Isolated Object Caches #

# Site 1
wordpress_sites:
  site1.com:
    cache:
      enabled: true
    object_cache:
      enabled: true
      provider: redis
      database: 0      # Redis DB 0

# Site 2
wordpress_sites:
  site2.com:
    cache:
      enabled: true
    object_cache:
      enabled: true
      provider: redis
      database: 1      # Redis DB 1

Mixed Cache Strategies #

# High-traffic marketing site (page cache only)
wordpress_sites:
  marketing.com:
    cache:
      enabled: true
      duration: 300s    # 5-minute page cache

# Database-heavy app (both caches)
wordpress_sites:
  app.com:
    cache:
      enabled: true
      duration: 30s
    object_cache:
      enabled: true
      provider: redis   # Adds object caching
      database: 0

Customizing Redis Configuration #

Global Redis Settings #

You can customize Redis settings in group_vars/all/main.yml:

# Increase memory allocation (default: 256mb)
redis_maxmemory: 512mb

# Change eviction policy (default: allkeys-lru)
redis_maxmemory_policy: allkeys-lru

# Enable Redis password
redis_requirepass: your_secure_password

# Persistence settings
redis_appendonly: "yes" # Enable AOF persistence

Advanced Configuration #

For more advanced Redis configuration, you can override any setting in group_vars/all/main.yml:

redis_extra_config:
  tcp-backlog: 511
  tcp-keepalive: 300
  supervised: systemd

Advanced Configurations #

Custom Redis Settings per Site #

wordpress_sites:
  example.com:
    cache:
      enabled: true
    object_cache:
      enabled: true
      provider: redis
      host: 127.0.0.1
      port: 6379
      database: 0
      password: secret_password
      prefix: custom_prefix_

Memcached Sessions + Redis Object Cache #

# In group_vars/all/main.yml
memcached_sessions: true # Use Memcached for PHP sessions

# In wordpress_sites.yml
wordpress_sites:
  example.com:
    cache:
      enabled: true # FastCGI page cache
    object_cache:
      enabled: true # Redis object cache
      provider: redis
      database: 0

This setup uses three different cache systems:

• Memcached: PHP sessions
• Redis: WordPress object cache
• FastCGI: Page cache

Monitoring #

Monitor Redis usage:

# Redis CLI
redis-cli

# Inside Redis CLI
INFO memory
INFO stats

# Monitor real-time commands
redis-cli MONITOR