how to define a general mount point in docker compose - docker

Question

I would like to define a general mount volume - along with all the options I would like to have it associated - that can be reused across multiple services. In fact, I'm developing a project which uses the same source for several microservices.
That way, the volume will be simpler to manage and modify.
To start off, I used the old way which took advantage of volumes_from:
shared:
image: phusion/baseimage
volumes:
- ./code:/var/www/html
nginx:
build: docker/nginx
ports:
- "8080:80"
links:
- php
volumes_from:
- shared
This works, but I had to define a shared service to make it work. As of the 3.0 version, volumes can be used, so I would like to define a general volume and use it into my nginx service, but I'm not finding the right syntax:
version: '3.3'
volumes:
vol_test:
type: bind
source: ./code
target: /var/www/html
volume:
nocopy: true
services:
nginx:
build: docker/nginx
ports:
- "8080:80"
volumes:
- vol_test
Update
I've found that defining a volume the way I want could not be possible, since the following definition:
volumes:
data-volume:
type: bind
source: ./code
target: /var/www/html
volume:
nocopy: true
will produce this output when calling docker-compose up:
ERROR: The Compose file './docker-compose.yml' is invalid because:
volumes.data-volume value Additional properties are not allowed ('volume', 'source', 'type', 'target' were unexpected)
I guess I still have to use the volumes_from way then. Can anybody confirm that?

Answer 1

I can confirm your observation: If you want to mount a host directory, you'll have to use the bind mount syntax.

Answer 2

You do not have to use volume_from anymore. Form
https://docs.docker.com/compose/compose-file/#volumes:
But, if you want to reuse a volume across multiple services, then
define a named volume in the top-level volumes key. Use named volumes
with services, swarms, and stack files.
They even specifically address your issue:
Note: The top-level volumes key defines a named volume and references it from each service’s volumes list. This replaces
volumes_from in earlier versions of the Compose file format. See Use
volumes and Volume Plugins for general information on volumes.
So, for a MWE I defined an empty volume and referenced it in two services. This is the compose file:
version: '3.3'
volumes:
vol_test:
services:
reader:
image: ubuntu
tty: true
command: bash -c "sleep 1; cat /volume/file;exit 0"
volumes:
- vol_test:/volume
writer:
image: ubuntu
tty: true
command: bash -c "date | tee /volume/file; exit 0"
volumes:
- vol_test:/volume
This gives us the following behavior:
$ date; docker-compose up
So 27. Aug 11:54:13 CEST 2017
Creating network "dockercomposetest_default" with the default driver
Creating dockercomposetest_writer_1 ...
Creating dockercomposetest_reader_1 ...
Creating dockercomposetest_writer_1
Creating dockercomposetest_reader_1 ... done
Attaching to dockercomposetest_writer_1, dockercomposetest_reader_1
writer_1 | 27 09:54:15 UTC 2017
reader_1 | 27 09:54:15 UTC 2017
Gracefully stopping... (press Ctrl+C again to force)