How to deal with persistent storage (e.g. database

Question

How do people deal with persistent storage for your Docker containers?

I am currently using this approach: build the image, e.g. for PostgreSQL, and then start the container with

docker run --volumes-from c0dbc34fd631 -d app_name/postgres

IMHO, that has the drawback, that I must not ever (by accident) delete container "c0dbc34fd631".

Another idea would be to mount host volumes "-v" into the container, however, the userid within the container does not necessarily match the userid from the host, and then permissions might be messed up.

Note: Instead of --volumes-from 'cryptic_id' you can also use --volumes-from my-data-container where my-data-container is a name you assigned to a data-only container, e.g. docker run --name my-data-container ... (see the accepted answer)

Answer 1

While this is still a part of Docker that needs some work, you should put the volume in the Dockerfile with the VOLUME instruction so you don't need to copy the volumes from another container.

That will make your containers less inter-dependent and you don't have to worry about the deletion of one container affecting another.

Answer 2

In Docker release v1.0, binding a mount of a file or directory on the host machine can be done by the given command:

$ docker run -v /host:/container ...

The above volume could be used as a persistent storage on the host running Docker.

Answer 3

Use Persistent Volume Claim (PVC) from Kubernetes, which is a Docker container management and scheduling tool:

Persistent Volumes

The advantages of using Kubernetes for this purpose are that:

• You can use any storage like NFS or other storage and even when the node is down, the storage need not be.
• Moreover the data in such volumes can be configured to be retained even after the container itself is destroyed - so that it can be reclaimed, if necessary, by another container.

Answer 4

If you want to move your volumes around you should also look at Flocker.

From the README:

Flocker is a data volume manager and multi-host Docker cluster management tool. With it you can control your data using the same tools you use for your stateless applications by harnessing the power of ZFS on Linux.

This means that you can run your databases, queues and key-value stores in Docker and move them around as easily as the rest of your application.

Answer 5

It depends on your scenario (this isn't really suitable for a production environment), but here is one way:

Creating a MySQL Docker Container

This gist of it is to use a directory on your host for data persistence.

Answer 6

Docker 1.9.0 and above

Use volume API

docker volume create --name hello
docker run -d -v hello:/container/path/for/volume container_image my_command

This means that the data-only container pattern must be abandoned in favour of the new volumes.

Actually the volume API is only a better way to achieve what was the data-container pattern.

If you create a container with a -v volume_name:/container/fs/path Docker will automatically create a named volume for you that can:

1. Be listed through the docker volume ls
2. Be identified through the docker volume inspect volume_name
3. Backed up as a normal directory
4. Backed up as before through a --volumes-from connection

The new volume API adds a useful command that lets you identify dangling volumes:

docker volume ls -f dangling=true

And then remove it through its name:

docker volume rm <volume name>

As @mpugach underlines in the comments, you can get rid of all the dangling volumes with a nice one-liner:

docker volume rm $(docker volume ls -f dangling=true -q)
# Or using 1.13.x
docker volume prune

Docker 1.8.x and below

The approach that seems to work best for production is to use a data only container.

The data only container is run on a barebones image and actually does nothing except exposing a data volume.

Then you can run any other container to have access to the data container volumes:

docker run --volumes-from data-container some-other-container command-to-execute

• Here you can get a good picture of how to arrange the different containers.
• Here there is a good insight on how volumes work.

In this blog post there is a good description of the so-called container as volume pattern which clarifies the main point of having data only containers.

Docker documentation has now the DEFINITIVE description of the container as volume/s pattern.

Following is the backup/restore procedure for Docker 1.8.x and below.

BACKUP:

sudo docker run --rm --volumes-from DATA -v $(pwd):/backup busybox tar cvf /backup/backup.tar /data

• --rm: remove the container when it exits
• --volumes-from DATA: attach to the volumes shared by the DATA container
• -v $(pwd):/backup: bind mount the current directory into the container; to write the tar file to
• busybox: a small simpler image - good for quick maintenance
• tar cvf /backup/backup.tar /data: creates an uncompressed tar file of all the files in the /data directory

RESTORE:

# Create a new data container
$ sudo docker run -v /data -name DATA2 busybox true
# untar the backup files into the new container᾿s data volume
$ sudo docker run --rm --volumes-from DATA2 -v $(pwd):/backup busybox tar xvf /backup/backup.tar
data/
data/sven.txt
# Compare to the original container
$ sudo docker run --rm --volumes-from DATA -v `pwd`:/backup busybox ls /data
sven.txt

Here is a nice article from the excellent Brian Goff explaining why it is good to use the same image for a container and a data container.