Which redis port to use for object caching or, other custom uses
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This article is to assist customers with using the proper redis port to use for object caching, or for any other use case requiring Redis access. Examples where you'd need to use this are with the redis-cache plugin, which you'd need to use if you want object caching when also using Advanced Custom Fields Pro - Currently Advanced Custom Fields does not work with Pagely's own Redis object-cache.php drop-in.
Many object caching plugins will default to port 6379. It is extremely important that port 6379 is not utilized. The answer is always to utilize 6380. Using port 6379 will lose important configuration data and cause your site(s) to become unavailable until that data gets reapplied.
As an example, here's how we would configure the redis-cache plugin:
1. Define the Redis Port and Cache Key
Note: This step must be performed before installing the redis-cache plugin.
Edit the wp-config.php file for the app you are working on. Add the define for the Redis port and the cache key. The cache key has to be unique for each app. Two apps can not share the same cache key.
define('WP_REDIS_PORT', 6380); define('WP_CACHE_KEY_SALT','my-site-nickname-here');
If you are on an HA plan, you'll also need to specify the private IP address of the primary node. This can be gained by running ifconfig on the primary server and looking for a 10.x.x.x IP:
These constants are specific to the redis-cache plugin. Please consult the documentation for any other plugins in order to determine the correct definitions it may need.
2. Install the Redis-Cache Plugin
You can install it via the WP dashboard or using the following command via the app root:
wp plugin install redis-cache
3. Activate the Plugin and Verify the Redis Port/Cache Key are Correct
Log into the WP dashboard and activate the redis-cache plugin (this can also be done via command line). Once the plugin is activated go to Settings --> Redis on the left panel of the dashboard. In this section, verify the port is 6380 and that your cache key prefix is set. Once everything looks good, click "Enable Object Cache"