Step 5: Configure Wordpress to use Redis 

Table of Contents

Step 5: Configure Wordpress to use Redis
- Connect WP to Redis
- Troubleshooting

We know that our Redis Docker container is working. Now, let’s configure Wordpress to use our new service.

Log into Wordpress at http://blog.example.com/wp-admin
Add the Redis Object Cache plugin
1. Plugins -> Add New -> Search for Redis Object Cache
2. Install and then activate it
Go to the plugin configuration panel
1. Settings -> Redis
Click Enable Object Cache
Click Show Diagnostics

You will notice that the status reads Not Connected. Clicking Show Diagnostics will show additional details. You will also notice that the host is 127.0.0.1. However, our Redis server is running on a different host, not on the localhost (127.0.0.1). From the perspective of Wordpress, localhost is container wordpressdocker_wordpress_1. Redis is running on container wordpressdocker_redis_1.

Docker knows about this container because we included it in the depends_on property. So, we only need to set the server address to redis. Docker will take care of the rest of the work.

Connect WP to Redis 

The Redis plugin help document page provides the information on variables that we can use to configure Redis to work without Docker container.

WP_REDIS_HOST: Defines a host other than 127.0.0.1

WP_CACHE_KEY_SALT: Separates the cache keys of Wordpress from other services that might use the same Redis instance. It guarantees uniqueness.

Add these two variables to your wp-config.php file. You can change the WP_CACHE_KEY_SALT to something unique.

define('WP_REDIS_HOST', 'redis');
define('WP_CACHE_KEY_SALT', 'wp-docker-5DknvYepdjyJMo8gDqrLhrpAJUQ');

We can modify wp-config.php easily because it is part of the Wordpress volume data. Nifty!

nano wordpress/wp-config.php

File contents of wp-config.php

define('WP_REDIS_HOST', 'redis');
define('WP_CACHE_KEY_SALT', 'wp-docker-5DknvYepdjyJMo8gDqrLhrpAJUQ');

// ** MySQL settings - You can get this info from your web host ** //
/** The name of the database for WordPress */
define('DB_NAME', 'wordpress');
.
.
.

Refresh the webpage. The status should have updated.

Overview Output

Status:    Connected
Client:    Predis (v1.1.1)
Key Prefix:    wp-docker-5DknvYepdjyJMo8gDqrLhrpAJUQ

You can see the cached information in the Diagnostics frame.

Diagnostics Output

Status: Connected
Client: Predis (v1.1.1)
Drop-in: Valid
Ping: PONG
Redis Extension: Not Found
Predis Client: 1.1.1
PHP Version: 7.2.16
Multisite: No
Global Prefix: "wp_"
Blog Prefix: "wp_"
WP_REDIS_HOST: "redis"
WP_CACHE_KEY_SALT: "wp-docker-5DknvYepdjyJMo8gDqrLhrpAJUQ"
Global Groups: {"0":"blog-details","1":"blog-id-cache","2":"blog-lookup","3":"global-posts","4":"networks","5":"rss","6":"sites","7":"site-details","8":"site-lookup","9":"site-options","10":"site-transient","11":"users","12":"useremail","13":"userlogins","14":"usermeta","15":"user_meta","16":"userslugs","33":"blog_meta"}
Ignored Groups: ["counts","plugins","themes"]
Dropins:
 - Redis Object Cache Drop-In v1.4.1 by Till Krüss
Plugins:
 - Akismet Anti-Spam v4.1.1 by Automattic (Inactive)
 - Hello Dolly v1.7.1 by Matt Mullenweg (Inactive)
 - Redis Object Cache v1.4.1 by Till Krüss (Active)

Troubleshooting 

Do you need to troubleshoot this further? Open a shell connection to the Wordpress docker container.
```
docker exec -it wordpressdocker_wordpress_1 /bin/sh
```

Add some essential tools

apt update && apt install -y redis-tools iputils-ping

Output

root@vps298933:~/wordpress-docker# docker exec -it wordpressdocker_wordpress_1 /bin/sh
# apt update && apt install -y redis-tools iputils-ping
Get:1 http://security-cdn.debian.org/debian-security stretch/updates InRelease [94.3 kB]
Get:2 http://security-cdn.debian.org/debian-security buster/updates InRelease [38.3 kB]
Get:4 http://security-cdn.debian.org/debian-security stretch/updates/main amd64 Packages [481 kB]
Ign:3 http://cdn-fastly.deb.debian.org/debian stretch InRelease
Get:5 http://cdn-fastly.deb.debian.org/debian stretch-updates InRelease [91.0 kB]
Get:6 http://cdn-fastly.deb.debian.org/debian buster InRelease [158 kB]
Get:7 http://cdn-fastly.deb.debian.org/debian buster-updates InRelease [46.8 kB]
Get:8 http://cdn-fastly.deb.debian.org/debian stretch-updates/main amd64 Packages [11.1 kB]
Get:9 http://cdn-fastly.deb.debian.org/debian stretch Release [118 kB]
Get:10 http://cdn-fastly.deb.debian.org/debian buster/main amd64 Packages [7887 kB]
Get:11 http://cdn-fastly.deb.debian.org/debian stretch Release.gpg [2434 B]
Get:12 http://cdn-fastly.deb.debian.org/debian stretch/main amd64 Packages [7084 kB]
Fetched 16.0 MB in 5s (3165 kB/s)
Reading package lists... Done
Building dependency tree
Reading state information... Done
All packages are up to date.
Reading package lists... Done
Building dependency tree
Reading state information... Done
The following additional packages will be installed:
  libcap2 libcap2-bin libjemalloc1 libpam-cap
Suggested packages:
  ruby-redis
The following NEW packages will be installed:
  iputils-ping libcap2 libcap2-bin libjemalloc1 libpam-cap redis-tools
0 upgraded, 6 newly installed, 0 to remove and 0 not upgraded.
Need to get 667 kB of archives.
After this operation, 1863 kB of additional disk space will be used.
.
.
.

Test the connection to the Redis server.

Note

We have to specify the host using the -h switch because Redis is running on a different host called redis.

Ping the redis server using ping to test the network connection.
Ping redis using redis-cli to test the server functionality
View server info using redis-cli

Commands

ping redis                       #Checks the network connection
redis-cli -h redis ping          #Checks server response
redis-cli -h redis info server   #View the server info

Output

# ping redis
PING redis (192.168.192.2) 56(84) bytes of data.
64 bytes from wordpressdocker_redis_1.wordpressdocker_default (192.168.192.2): icmp_seq=1 ttl=64 time=0.211 ms
64 bytes from wordpressdocker_redis_1.wordpressdocker_default (192.168.192.2): icmp_seq=2 ttl=64 time=0.100 ms
^C
--- redis ping statistics ---
2 packets transmitted, 2 received, 0% packet loss, time 1001ms
rtt min/avg/max/mdev = 0.100/0.155/0.211/0.056 ms
#
# redis-cli -h redis ping
PONG
#
# redis-cli -h redis info server
# Server
redis_version:5.0.4
redis_git_sha1:00000000
redis_git_dirty:0
redis_build_id:c6d7e1572d62bb79
redis_mode:standalone
os:Linux 4.15.0-46-generic x86_64
arch_bits:64
multiplexing_api:epoll
atomicvar_api:atomic-builtin
gcc_version:6.3.0
process_id:1
run_id:21c1137b7c733b539977f3a7f6646a0b95a15654
tcp_port:6379
uptime_in_seconds:2510
uptime_in_days:0
hz:10
configured_hz:10
lru_clock:10425442
executable:/data/redis-server
config_file:
#
.
.
.

If these commands are successful, then the problem is in Wordpress.
Type exit to leave the SSH session.
```
exit
```
Check the wp-config.php file.

Step 5: Configure Wordpress to use Redis

Connect WP to Redis

Troubleshooting

Step 5: Configure Wordpress to use Redis 

Connect WP to Redis 

Troubleshooting 