Docker can't connect to redis from another service

It looks like your redis image is configured to listen on 127.0.0.1 rather than all interfaces. This is not an issue with the default redis images, so either use the official image from docker hub, or correct your configuration to listen on 0.0.0.0.

You'll be able to verify this with netshoot:

docker run --rm --net container:app_redis nicolaka/netshoot netstat -ltn

In the redis conf, listening on all interface is done by commenting out the "bind" line in redis.conf.