I'm having trouble creating an image of a docker redis container with the data in the redis database. At the moment I'm doing this:
docker pull redis
docker run --name my-redis -p 6379:6379 -d redis
redis-cli
127.0.0.1:6379> set hello world
OK
127.0.0.1:6379> save
OK
127.0.0.1:6379> exit
docker stop my-redis
docker commit my-redis redis_with_data
docker run --name my-redis2 -p 6379:6379 -d redis_with_data
redis-cli
127.0.0.1:6379> keys *
(empty list or set)
I'm obviously not understanding something pretty basic here. Doesn't docker commit create a new image from an existing container?
okay, i've been doing some digging. The default redis image on hub.docker uses a data-volume which is then mounted at /data in a container. In order to share this volume between containers, you have to start a new container with the following argument:
docker run -d --volumes-from <name-of-container-you-want-the-data-from> \
--name <new-container-name> -p 6379:6379 redis
Note that the order of the arguments is important, otherwise docker run will fail silently.
docker volume ls
will tell you which data volumes have already been created by docker on your computer. I haven't yet found a way to give these volumes a trivial name, rather than a long random string.
I also haven't yet found a way to mount a data-volume, but rather just use the --volumes-from command.
Okay. I now have it working, but it's cludgey.
With
docker volume ls
docker volume inspect <id of docker volume>
you can find the path of the docker volume on the local file-system. You can then mount this in a new container as follows:
docker run -d -v /var/lib/docker/volumes/<some incredibly long string>/_data:/data \
--name my-redis2 -p 6379:6379 redis
This is obviously not the way you're meant to do this. I'll carry on digging.
I put all that i've discovered upto now in a blog post: my blog post on medium.com
Maybe that will be useful for somebody
Data in docker is not persistent, when you restart the container your data will be gone. To prevent this you have to share a map on the host machine with your container. When you container restarts it will get the data from the map on the host.
You can read more about it in the Docker docs: https://docs.docker.com/engine/tutorials/dockervolumes/#data-volumes
From the redis container docs:
Run redis-server
docker run -d --name redis -p 6379:6379 dockerfile/redis
Run redis-server with persistent data directory. (creates dump.rdb)
docker run -d -p 6379:6379 -v <data-dir>:/data --name redis dockerfile/redis
Run redis-server with persistent data directory and password.
docker run -d -p 6379:6379 -v <data-dir>:/data --name redis dockerfile/redis redis-server /etc/redis/redis.conf --requirepass <password>
Using data volume and sharing RDB file manually is not ugly, actually that's what data volume is designed for, to separate data from container.
But if you really need/want to save data to image and share it that way, you can just change the redis working directory from volume /data to somewhere else:
Option 1 is changing --dir when start the redis container:
docker run -d redis --dir /tmp
Then you can follow your steps to create new image. Note that only /tmp could be used by this method due to permission issue.
Option 2 is creating a new image with changed WORKDIR:
FROM redis
RUN mkdir /opt/redis && chown redis:redis /opt/redis
WORKDIR /opt/redis
Then docker build -t redis-new-image and use this image to do your job.