Leverage WordPress Object Cache with Vultr Managed Databases for Redis

Updated on November 12, 2023
Leverage WordPress Object Cache with Vultr Managed Databases for Redis header image

Introduction

Redis is an open-source in-memory database that works as an object caching solution for Content Management Systems (CMS) such as WordPress. Object caching keeps database query results in memory and delivers them faster when users make similar requests. For example, when a WordPress page loads on your site, the MySQL database server sends the first response, and any additional requests receive responses from the WordPress Object Cache memory

By integrating WordPress with a Vultr Managed Database for Redis, the request handling process between your MySQL database gets improved with Object Caching enabled by the Redis database which improves your general site performance. Follow the steps in this article to leverage WordPress Object Cache with a Vultr Managed Database for Redis

Prerequisites

Before you begin:

Install the WordPress Redis Object Cache Plugin

Redis Object Cache is a persistent object cache plugin that stores MySQL database responses to an existing Redis database. When a WordPress user makes a request, the MySQL database returns a result and the generated response is cached to your Redis database and served until expiry. Install the Redis Object Cache plugin on your WordPress site as described in the steps below.

  1. Using a web browser such as Chrome, log in to your WordPress administrator dashboard

     https://example.com/wp-admin
  2. On the left navigation bar, find and click Plugins

  3. On the Plugins page, click Add New

  4. Enter the keyword Redis Object Cache in the Search Plugins field

  5. Within the search results, find the Redis Object Cache plugin

    Install the Redis Object Cache Plugin on WordPress

  6. Click Install Now to install the plugin on your WordPress site

  7. Click Activate to enable the plugin

Configure the Redis Object Cache Plugin

To enable the Redis Object Cache plugin and store all WordPress database responses to your Vultr Managed Database for Redis, make changes to your wp-config.php file as described below.

  1. Using SSH, access your WordPress server as a non-root user with sudo privileges

     $ ssh example-user@SERVER-IP

    When using a control panel such as cPanel or Plesk without SSH access, enable Redis on your account to integrate PHP with Redis

  2. Install the PHP Redis extension

    On Ubuntu or Debian servers:

     $ sudo apt install php-redis

    On CentOS, Rocky Linux, or RHEL-based servers:

     $ dnf install php-redis
  3. Navigate to your WordPress web root directory. Usually, /var/www/html or /var/www/public_html

     $ cd /var/www/html
  4. List files in the directory to verify that all WordPress files are available

     $ ls
  5. Back up the WordPress wp-config.php file

     $ sudo cp wp-config.php wp-config.ORIG
  6. Using a text editor such as Nano, edit the wp-config.php file

     $ sudo nano wp-config.php
  7. Find the following WordPress debugging directive

     define( 'WP_DEBUG', false );
  8. Change it from false to true to display any configuration errors

     define( 'WP_DEBUG', true );
  9. Add the following configurations at the end of the file. Replace all example values with your actual Vultr Managed Database for Redis details

     define( 'WP_REDIS_SCHEME', 'tls' );
     define( 'WP_REDIS_HOST', 'vultr-prod-example.vultrdb.com' );
     define( 'WP_REDIS_PORT', 16752 );
     define( 'WP_REDIS_PASSWORD', 'Vultr-Redis-Password' );
     define( 'WP_REDIS_DATABASE', 0 );
     define( 'WP_REDIS_TIMEOUT', 1 );
     define( 'WP_REDIS_READ_TIMEOUT', 1 );
     define( 'WP_REDIS_RETRY_INTERVAL', 3 );

    Save and close the file.

    Below is what the above Redis connection directives represent:

    • WP_REDIS_SCHEME: Defines the connection mechanism to your Redis database tls enforces a secure TLS connection to the database
    • WP_REDIS_HOST: Sets the Vultr Managed Database for Redis hostname
    • WP_REDIS_PORT: Sets the Vultr Managed Database for Redis connection port
    • WP_REDIS_PASSWORD: Sets the Vultr Managed Database for Redis default user password to use for authentication to the database
    • WP_REDIS_DATABASE: Defines the target Redis database to bind your WordPress site. Redis Cluster database values range from 0 to 15, select your desired database number depending on your Vultr Managed Database for Redis cluster usage
    • WP_REDIS_TIMEOUT: Sets the maximum time in seconds a connection to the Redis database should wait before terminating in case of a failure. 1 sets the waiting time to 1 second
    • WP_REDIS_READ_TIMEOUT: Defines the maximum time WordPress should wait to receive Redis responses. When the time elapses, the operation becomes unsuccessful
    • WP_REDIS_RETRY_INTERVAL: Sets the time in milliseconds a failed connection to the Redis database should restart. 3 instructs WordPress to retry the connection after every 3 milliseconds, 1000 sets the retry interval to 1 second
  10. In a new web browser session, access your WordPress administrator dashboard

     https://example.com/wp-admin
  11. On the main navigation menu, find and click Settings

  12. Select Redis from the list of dropdown options

    Open the Redis Plugin Page

  13. Within the Redis Object Cache plugin page, verify that the Redis value is Reachable

  14. Navigate to Diagnostics and verify that your wp-config.php changes display in the log output like the one below:

     Status: Drop-in not installed
     PhpRedis: 5.1.1
     Metrics recorded: 0
     Filesystem: Working
     WP_REDIS_SCHEME: "tcp"
     WP_REDIS_HOST: "vultr-prod-example.vultrdb.com"
     WP_REDIS_PORT: 16752
     WP_REDIS_DATABASE: 0
     WP_REDIS_TIMEOUT: 1
     WP_REDIS_READ_TIMEOUT: 1
     WP_REDIS_PASSWORD: ••••••••
     Drop-ins: []
  15. Navigate back to the Overview tab, and click Enable Object Cache to connect your Vultr Managed Database for Redis with your WordPress Site

    Enable Redis Object Cache on WordPress

  16. When successful, verify that the Status field changes to Connected and the connection details display on your plugin page

    Connect the WordPress Redis Object Cache Plugin to a Vultr Managed Database for Redis

    If the connection fails and the Status field is Not Connected, navigate to Diagnostics and view the details on why your connection fails

Test the WordPress Object Caching Data

To test that your WordPress data is available in the Vultr Managed Database for Redis as the Object Cache storage, install the Redis CLI tool on your server and view your cached data as described below.

  1. Using SSH, access your WordPress server console

     $ ssh example-user@SERVER-IP
  2. Install the Redis CLI tool on your server

     $ sudo apt install redis
  3. Using your Vultr Managed Database for Redis connection string, connect to the database cluster

     $ redis-cli -u rediss://default:[YOUR_PASSWORD]@[-vultrdb.com]:16752
  4. When successful, verify that the Redis cluster works correctly

     > ping

    Output:

     PONG
  5. Select your WordPress Redis database. For this article, the database 0 applied in your wp-config.php file

     > select 0
  6. View the available data in the database

     > keys *

    Your output should look like the one below:

     94) "wp:post-queries:wp_query-bd439aca13dc14dc82d1e7533b47b441-0.24954800 1695929332"
     95) "wp:default:is_blog_installed"
     96) "wp:post-queries:wp_query-58900d8f14e49bfe6854751899db67b8-0.14774800 1695929332"
     97) "wp:posts:9"
     98) "wp:site-transient:wp_remote_block_patterns_8b4fc2c6224785bc57d976c11baeaeb5"
     99) "wp:comment-queries:get_comments-fbb001ab5aa3f7e15b8511e52af82c41-0.72589800 1695928288"
     100) "wp:post-queries:wp_query-b0801891911659cc716c426655d11a0d-0.23627600 1695929330"
     101) "wp:post-queries:wp_query-916b5df869e5920ac3e40e95396e0e90-0.24954800 16959293320.23554800 1695929330"
     102) "wp:post-queries:wp_query-b53a158b77118c629e053f0d7bafbc03-0.26738100 16959293170.23184000 1695929317"
     103) "wp:post-queries:wp_query-4687a2847791544c62c28a7fe5e1a1a9-0.23275500 16959293170.23184000 1695929317"
     104) "wp:post-queries:wp_query-9efcb4c3e7cedb5ca63c3e3941fd10f3-0.22376600 1695929330"
     105) "wp:comment-queries:get_comments-a0c619f46f1580e85878c1b708cdefd9-0.72589800 1695928288"
     106) "wp:posts:5"

    As displayed in the above output, all cached WordPress database responses are available in the Vultr Managed Database for Redis. When users perform similar requests, the Vultr Managed Database for Redis sends the cached responses which increases the general site response time with no need for new MySQL database queries.

Troubleshooting

Depending on your WordPress configuration environment, you may encounter any of the following errors you can fix using the recommended solutions.

HTTP Error 500

The HTTP error 500 represents a configuration error within your web server files. For example, if the wp-config.php file has misconfigured values, PHP throws an error to the web server causing the error 500 notice. In case the above error displays, fix it in the steps below.

  1. Navigate to your web server logs directory. For example when using Nginx /var/log/nginx, Apache /var/log/apache2

     $ cd /var/log/nginx
  2. View the web server error logs

     $ sudo cat error.log

    When using custom error logs in your configuration, for example, example.com.error.log, view the file instead

    Output:

     2023/09/28 19:00:52 [error] 60867#60867: *972 FastCGI sent in stderr: "PHP message: PHP Fatal error:  Uncaught Error: Undefined constant "tls" in /var/www/example.com/wp-config.php:3
     Stack trace:
     #0 /var/www/example.com/wp-load.php(50): require_once()
     #1 /var/www/example.com/wp-admin/admin.php(34): require_once('...')
     #2 /var/www/example.com/wp-admin/options-privacy.php(10): require_once('...')
  3. Find the latest error entry returned at the time you load the WordPress site. For example, the above output points to a corrupted wp-config.php file. Rename the file

     $ sudo mv wp-config.php wp-config-error.php
  4. Recover the original wp-config.php file to fix the error

     $ sudo cp /var/www/example.com/wp-config-ORIG.php  /var/www/example.com/wp-config.php 
  5. View the contents of your error wp-config.php file and verify the source of the error. Usually, a string with missing single quotation marks '' can corrupt the file

  6. Revisit your WordPress site and verify that the HTTP error 500 does not display again. If persistent, view the latest web server error log entry

     https://example.com

Redis Object Cache Diagnostics Errors

  1. If you receive the following READ error:

     Ping:
     Connection Exception: read error on connection to vultr-prod-EXAMPLE.vultrdb.com:16752 (RedisException)
     Errors: [
         "read error on connection to vultr-prod-EXAMPLE.vultrdb.com:16752"

    Verify that you are using the correct Redis connection scheme in your wp-config.php file. By default, a Vultr Managed Database for Redis requires a tls connection

  2. If you receive the following Connection Refused error:

     Ping:
     Connection Exception: read error on connection to vultr-prod-a238a852-b0e6-44a5-ab05-e7148f81d820-vultr-prod-8c01.vultrdb.com:16752 (RedisException)
     Errors: [
         "Connection refused"
     ]

    Verify that the Vultr Managed Database for Redis details applied in your wp-config.php file are correct

  3. If you receive the following Redis Server Went Away error:

     Ping:
     Connection Exception: Redis server went away (RedisException)
     Errors: [
     Redis server went away"
     ]

    Verify your Vultr Managed Database for Redis cluster status that it's set to Running

    Vultr Managed Database for Redis Status

    Also, ensure that the Redis connection details are above all configurations in the wp-config.php file and below the <? php directive

  4. Error Establishing a RedisConnection

    Error establishing a Redis Database Connection

    Add the Redis connection details at the top of the wp-config.php file, but below the <? php directive

Conclusion

You have integrated WordPress with a Vultr Managed Database for Redis Cluster. Using one managed database cluster, you can connect multiple WordPress databases to different database IDs and perform object caching to improve your general site performance. Each time site visitors view and visit your WordPress site, database responses get cached to your Redis database which offers faster responses with the same data. For more Redis Object Cache Plugin configuration options, visit the project repository.

Next Steps

To implement more solutions and leverage your WordPress server resources, visit the following resources: