Unfortunately with Docker, things become a little tricky when it comes to Redis configuration file, and the answer voted as best (im sure from people that did'nt actually tested it) it DOESNT work.
But what DOES WORK, fast, and without husles is this:
command: redis-server --bind redis-container-name --requirepass some-long-password --maxmemory 256mb --maxmemory-policy allkeys-lru --appendonly yes
You can pass all the variable options you want in the command section of the yaml docker file, by adding "--" in the front of it, followed by the variable value.
Never forget to set a password, and if possible close the port 6379.
Τhank me later.
PS: If you noticed at the command, i didnt use the typical 127.0.0.1, but instead the redis container name. This is done for the reason that docker assigns ip addresses internally via it's embedded dns server. In other words this bind address becomes dynamic, hence adding an extra layer of security.
If your redis container is called "redis" and you execute the command docker inspect -f '{{range .NetworkSettings.Networks}}{{.IPAddress}}{{end}}' redis
(for verifying the running container's internal ip address), as far as docker is concerned, the command give in docker file, will be translated internally to something like: redis-server --bind 172.19.0.5 --requirepass some-long-password --maxmemory 256mb --maxmemory-policy allkeys-lru --appendonly yes