Integrate redis docker container and use it as LRU cache

[Pindar]

No description provided.

[mbabineau]

Thanks, it'll be great to get this cache in.

I may be missing something, but where are REDIS_PORT_6379_TCP_ADDR, REDIS_PORT_6379_TCP_PORT, CACHE_LRU_REDIS_DB, and CACHE_LRU_REDIS_PASSWORD getting set?

Also, it would be good to start redis-cache in the same way as docker-registry - that is, via runit. This ensures the container will restart in case of a failure. Note that this will break the use of --link, so maybe we use host networking (docker run --net=host) for both containers instead?

[Pindar]

@mbabineau hey yea so far it seems to work on mine but let's improve it further.

• the environment variables are set through the standard docker container linking (specially for the redis you find information on this page https://registry.hub.docker.com/_/redis/). The CACHE_LRU_REDIS_DB / CACHE_LRU_REDIS_PASSWORD variables are not set we could strip them out.
• regarding the startup with runit: so far as I have understood is that if you are running a docker container as deamon (-d) the default docker configuration would restart this container after a reboot automatically -- so there wouldn't be a need of runit/upstart but I might be wrong in this case because I haven't tested it yet. I just thought that if this is true we could get rid of runit and the custom AMI entirely what would make things a bit leaner (but this should be made in a separate pull request I guess)
• the docker linking would also work with runit if we can start the services in the correct order -- is this possible?

I have it running with S3 redirect and the redis cache and it's working fine so far but the cache is not so much in use because of the S3 redirects.