Share a named volume among several services

General
1

First of all here is my scenario

+ tree
├── 1.yml
└── 2.yml

+ cat 1.yml
services:
    service1:
        image: bash
        volumes:
            - dir:/dir
volumes:
    dir:

+ cat 2.yml
services:
    service2:
        extends:
            file: 1.yml
            service: service1
        volumes:
            - dir:/dir

To notice

        extends:
            file: 1.yml
            service: service1

Now a little attention

+ docker compose -f 2.yml run --rm service2 ls -dl /dir
service "service2" refers to undefined volume dir: invalid compose project
+ docker compose -f 1.yml run --rm service1 ls -dl /dir
drwxr-xr-x    2 root     root          4096 Jul 26 08:22 /dir

As you can see, if I use service2, there is any problem.
While if I use service1… everything is ok.

Why?

2

You need to define a volumes: section in every compose file (doc).

Make sure to set a name:, as compose usually prefixes volumes per compose file.

1 Like
3

If I am not mistaken, the prefixes to container and volume names are based on the COMPOSE_PROJECT_NAME, and not the compose file name

The project name defaults to the name of the directory the compose files are in

@bluepuma77

1 Like
4

But if the section is particularly nourished

volumes:
    dir:
    dir2:
    dir3:
    dir4:
    dir5:
    dir6:
    dir7:
    ...

replicating it on each file I see it a too uncomfortable thing.
And if for example after a month I have to make a change, I have to remember to replicate it on each compose file: which is impossible, because I would not be able to remember the names of each individual compose file.

5

Why not simply place all services in the same compose file?

Alternatively you should be able to use a common base and then an extra service file on top.

docker compose -f docker-compose.base.yml -f docker-compose.override.yml up
1 Like