Docker: redis in different container, redis-cli connects, redis object cahce not

Which port is your Redis installation listening on and which is it mapped to in the container?

It’s mapped the the default port and yes, it is mapped to the container, hence the command redis-cli works:

redis-cli -h redis -p 6379
redis:6379> ping
PONG

This is the command running inside the wordpress container. So there is a connection to the redis installation active in the redis container.

Can you run sudo netstat -lntp in both the host and its container?

Sure thing, and thank you for your help:

From the wordpress container:

bash-4.3# sudo netstat -lntp                                                                                                                       
Active Internet connections (only servers)
Proto Recv-Q Send-Q Local Address           Foreign Address         State       PID/Program name    
tcp        0      0 127.0.0.1:9000          0.0.0.0:*               LISTEN      61/php-fpm.conf)
tcp        0      0 0.0.0.0:80              0.0.0.0:*               LISTEN      62/nginx: master pr
tcp        0      0 :::80                   :::*                    LISTEN      62/nginx: master pr

From the host OS (CoreOS)

Active Internet connections (only servers)
Proto Recv-Q Send-Q Local Address           Foreign Address         State       PID/Program name    
tcp6       0      0 :::22                   :::*                    LISTEN      1/systemd           
tcp6       0      0 :::3000                 :::*                    LISTEN      12444/docker-proxy  
tcp6       0      0 :::443                  :::*                    LISTEN      2142/docker-proxy   
tcp6       0      0 :::64738                :::*                    LISTEN      10836/docker-proxy  
tcp6       0      0 :::2376                 :::*                    LISTEN      1/systemd           
tcp6       0      0 :::2222                 :::*                    LISTEN      12380/docker-proxy  
tcp6       0      0 :::8080                 :::*                    LISTEN      30383/docker-proxy  
tcp6       0      0 :::80                   :::*                    LISTEN      2151/docker-proxy   

This is from inside the redis container:

ctive Internet connections (only servers)
Proto Recv-Q Send-Q Local Address           Foreign Address         State       PID/Program name    
tcp        0      0 0.0.0.0:6379            0.0.0.0:*               LISTEN      -
tcp        0      0 :::6379                 :::*                    LISTEN      -

I just fought through this and discovered that my PHP define('WP_REDIS_HOST', 'redis'); was being added at the wrong time.

I was using a custom plugin (generated on container creation) to add a few defines. It turns out that this is too late – the defines needed to be in wp-config.php.

A quick custom PHP file with $r = new Redis(); $r->connect(...) was successful, even though the plugin itself was failing.

The timing issue was discovered by enabling WP_DEBUG and seeing that the PHP-Redis connection was failing (PHP warning message) on line 418 of wp-content/object-cache.php. After a var_dump($parameters); it became clear that my define()s were not being included early enough as the $parameters object didn’t have my own credentials. This makes sense – as an opcache, plugin behaviour should be included in caching, so the cache needs to be initialized before plugins.

During this process I disabled the password on the Redis container. Haven’t turned it back on yet, but it should work now…

Yes, indeed the position of the config lines is crucial.
I moved them now to just below the SALT and database configurations and it loads without issues.

Thanks guys for your help ??

Awesome!

If anyone is curious, my stack is here: https://github.com/emcniece/docker-wordpress

??
Here is my repo: https://github.com/Gymnae/docker-wordpress

The little snippet which adds the redis object config cache to wp-config.php

# sed redis config into config.php
sed -i "/#@-/a /** redis dropin */\n define( 'WP_REDIS_HOST', 'redis');\n define( 'WP_REDIS_CLIENT', 'pecl');" wp-config.php

I copied docker-entrypoint.sh and Dockerfile from the original wordpress docker image, but adjusted them to my (baseimages) needs