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:

  CONFIG_TEXT: 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 will be fixed in future updates.

Resolution

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

   For rpm-based OS (CentOS, RHEL, CloudLinux)

   # yum install gcc libmemcached-devel zlib-devel
   # yum install plesk-php56-devel plesk-php70-devel plesk-php71-devel plesk-php72-devel plesk-php73-devel

   For deb-based OS (Debian, Ubuntu)

   # apt install autoconf automake gcc libmemcached-dev libhashkit-dev pkg-config plesk-php..-dev zlib1g-dev

2. 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.