enketo_redis_* docker containers are sensitive to umask set at git clone time

[brontolosone]

Problem description

While setting up the docker containers per instructions, one can run into hard to debug problems. Symptom: the enketo_redis_* containers keep restarting which makes it so that the enketo container keeps restarting.

This turned out to be caused by redis not having read permissions for the redis config files bind-mounted into the container. Which turned out to be because of an assumption that these files will be world-readable on the host filesystem.

On Linux (maybe on OSX too? Is there a bind mount mechanism on OSX?), if one has an umask of 027, as one is totally entitled to have set, then after the git clone operation, the files/enketo/redis-enketo-*.conf files in the Central repo will be o=.
At container instantiation time these files are bind-mounted into the container. A bind mount doesn't change UIDs or permissions. Thus unless your host user UID happens to match the in-container redis uid (999), redis will crash on startup as it can't read its config file, leading to a docker restart loop on those containers.

One way to help users avoid this situation could be to simply amend the documentation.