Redis Object Cache plugin shows as Not connected

Symptoms

• The following optimization guide was implemented for Redis: How To Optimize WordPress With Redis And Docker

• WordPress > example.com > Log in > Plugins > Redis Object Cache Plugin > Settings shows as Not Connected:

  Not connected

• PHPRedis installed is 3.0:

  # rpm -qa | grep redis
  plesk-php73-redis-3.0.0-1centos.7.190906.1643.x86_64

Cause

Latest Redis required is PHPRedis 5.0.

This has been reported as bug ID PPP-45378 which has been fixed in Plesk 18.0.29.

Resolution

Workaround

At first, log into the server via SSH and prepare the environment:

• Then, use the following instructions to upgrade redis:

  Note: in the example below, instructions for PHP 7.3 are provided.

  1. Upgrade the redis extension:

     # /opt/plesk/php/7.3/bin/pecl upgrade redis

  2. It might show the following warning. Just press ‘Enter’ without specifying anything to continue the installation:

     # /opt/plesk/php/7.3/bin/pecl upgrade redis
     pecl/redis can optionally use PHP extension “igbinary” (version >= 2.0)
     pecl/redis can optionally use PHP extension “msgpack” (version >= 2.0)
     downloading redis-3.0.4.tgz …
     Starting to download redis-3.0.4.tgz (78,776 bytes)
     ………………done: 78,776 bytes
     15 source files, building
     running: phpize
     Configuring for:
     PHP Api Version: 20151012
     Zend Module Api No: 20151012
     Zend Extension Api No: 320151012
     libmemcached directory [no] :

  3. Register extension in configuration file:

     # echo “extension=redis.so” > /opt/plesk/php/7.3/etc/php.d/redis.ini

  4. Update PHP handlers information:

     # plesk bin php_handler –reread

  5. Restart Apache in Tools & Settings > Services Management.

     Note: In case FPM service is used, it is required to restart FPM service as well. It can be done through Tools & Settings > Services Management.