Why can't redis access the disk in docker-compose?

Question

I tried a very simple first test of a python app with a redis according to the docker documentation. This crashes after a while because redis cannot persist. I don't have a clue why. You can find the public repo here: Github repo

My current docker-compose.yml is:

web:
  build: .
  ports:
   - "5000:5000"
  volumes:
   - .:/code
  links:
   - redis
redis:
  image: redis:latest
  volumes:
  - ./data:/data

Edit: this is an excerpt of the log:

1:M 09 Feb 10:51:15.130 # Background saving error
1:M 09 Feb 10:51:21.072 * 100 changes in 300 seconds. Saving...
1:M 09 Feb 10:51:21.073 * Background saving started by pid 345
345:C 09 Feb 10:51:21.074 # Failed opening .rdb for saving: Permission denied
1:M 09 Feb 10:51:21.173 # Background saving error
1:M 09 Feb 10:51:27.011 * 100 changes in 300 seconds. Saving...
1:M 09 Feb 10:51:27.011 * Background saving started by pid 346
346:C 09 Feb 10:51:27.013 # Failed opening .rdb for saving: Permission denied

Edit2: this is the complete error Redis throws in python:

MISCONF Redis is configured to save RDB snapshots, but is currently not able to persist on disk. Commands that may modify the data set are disabled. Please check Redis logs for details about the error

The funny thing is, I don't do anything to the redis image.

Answer 1

It is a permission error, log into the redis container via docker exec -it redis_container_name bash and ensure it has write permissions on /data.

It probably does not, and you can fix it several ways: use a docker volume instead of bind-mounting the host, or try to fix permissions from the host by having matching uid/gid with the owner in the container.

Also, as stated in the docker hub page, you should set redis' command to:

web:
  build: .
  ports:
   - "5000:5000"
  volumes:
   - .:/code
  links:
   - redis
redis:
  image: redis:latest
  command: redis-server --appendonly yes
  volumes:
  - ./data:/data

if you intend to persist data.

Since your data folder has the wrong permissions set, start by deleting it and letting docker-compose make a new one.