“Error establishing a Redis connection” with dockerized WordPress 6.7.1

Hello Till,

I’m reaching out regarding an issue we’ve encountered when using the Redis Object Cache plugin with a fresh installation of WordPress 6.7.1. Despite following the official setup guidelines, our WordPress site fails with the following error:

Error establishing a Redis connection

Connection refused

WordPress is unable to establish a connection to Redis. This means that the connection information in your wp-config.php file are incorrect, or that the Redis server is not reachable.

• Is the correct Redis host and port set?
• Is the Redis server running?

If you need help, please read the?installation instructions.

To disable Redis, delete the object-cache.php file in the /wp-content/ directory.

Here are the details of our setup:

1. WordPress Version: 6.7.1 (fresh installation)
2. Redis Plugin Version: Redis Object Cache 2.5.4
3. Server Environment:
   • Dockerized Setup: Using docker-compose
   • Relevant Containers:
     • WordPress (wordpress:php8.0-fpm)
     • Redis (redis:alpine)
     • WP-CLI (custom-wordpress-cli built on the official WP-CLI image)
     • Nginx (nginx:alpine) for frontend
     • MariaDB (mariadb:latest) for the database
     • Varnish (varnish:stable) for caching
4. Redis Configuration:
   • Redis is running in the my-redis container and is reachable from other containers within the Docker bridge network (my_network).
   • Redis configuration: Default Alpine Redis settings (bind *, protected-mode no).
5. wp-config.php Constants for Redis
   • define("WP_REDIS_HOST", "my-redis");
   • define("WP_REDIS_PORT", 6379);
   • define("WP_REDIS_DATABASE", 0);
   • define("WP_REDIS_DEBUG", true);
   • define("WP_DEBUG", true);
   • define("WP_DEBUG_LOG", true);
   • define("WP_DEBUG_DISPLAY", false);
   • @ini_set("display_errors", 0);
   • define("WP_REDIS_TIMEOUT", 5);
   • define("WP_REDIS_READ_TIMEOUT", 5);
6. Plugin Behavior:
   • Activating the plugin creates the object-cache.php drop-in at /wp-content/.
   • The Redis server is accessible (PONG response from Redis CLI within the WordPress container).
   • Enabling Object Cache via the plugin causes the “Error establishing a Redis connection” issue.

Steps we’ve tried:

1. Verified network connectivity:
   • Pinged my-redis from the WordPress container (ping my-redis works).
   • Successfully executed redis-cli -h my-redis ping from the WordPress container (PONG response).
2. Reviewed Redis logs:
   • No errors in Redis logs, and CONFIG GET shows the expected settings (bind, protected-mode, etc.).
3. Tested Redis connectivity from WP-CLI:
   • WP-CLI reports Redis as reachable, but enabling Object Cache causes the same error.
4. Tried replacing the object-cache.php file:
   • Replaced it with the latest version from the plugin’s GitHub repository (branch: develop).
5. Reinstalled the plugin:
   • Deactivated, uninstalled, and reinstalled the Redis Object Cache plugin. The error persisted.
6. Checked for known compatibility issues:
   • Verified that Redis Object Cache 2.5.4 supports Redis 7.4.1 and PHP 8.0.

Summary of issue

• Redis is reachable and functional, yet WordPress fails to connect when Object Cache is enabled.
• The error specifically points to RedisException: Connection refused in /wp-content/object-cache.php.
• We suspect a compatibility issue between Redis Object Cache and WordPress 6.7.1 but have not found evidence of this in community forums or issue trackers.

Questions:

1. Are there known issues with the Redis Object Cache plugin and WordPress 6.7.1 or Redis 7.4.1?
2. Could this be related to the object-cache.php drop-in, or should we consider alternative configurations for Redis?
3. Are there any additional debug steps or alternative plugin versions (e.g., pre-releases) we should test?