Sharing volume between Docker containers

Question

I am using Docker to deploy some services and I want to share the Docker volumes between different containers.

Suppose I have a Docker container A which mounts a volume at /data. Here is its Dockerfile:

VOLUME /data

From my understanding, this will attach a volume to the container but it will not mount a host directory to the container. So the data inside this volume is still inside the container A.

I have another container B which provides an FTP service. It accesses the data under volume /public. Its Dockerfile is:

VOLUME /public

Now I want to link them together so that I can use B to manage A's data. From the Docker doc https://docs.docker.com/engine/userguide/containers/dockervolumes/ I shall use the --volumes-from flag to mount A's data volume to B. But this command will mount A's data to /data in B instead of /public, and in this case, the container B is not able to access the data. I didn't see any way to rename the mount point.

Any suggestions or best practices to handle this case?

---

The data-only container gives a good solution for this case. But if you want to use volumes-from and mount the data to different mount point, this question may be helpful! How to map volume paths using Docker's --volumes-from?

Answer 1

You may find a lot of pointers mentioning data-only containers and --volumes-from. However, since docker 1.9, volumes have become first class citizens, they can have names, and have more flexibility:

It's now easy to achieve the behavior you want, here's an example :

1. Create a named data volume with name service-data:

   docker volume create --name service-data
   

2. You can then create a container that mounts it in your /public folder by using the -v flag:

   docker run -t -i -v service-data:/public debian:jessie /bin/bash
   

   For testing purpose we create a small text file in our mapped folder:

   cd public
   echo 'hello' > 'hello.txt'
   

3. You may then attach your named volume to a second container, but this time under the data folder:

   docker run -t -i -v service-data:/data debian:jessie /bin/bash
   ls /data       #-->shows "hello.txt"
   

Just remember, if both containers are using different images, be careful with ownership and permissions!