Re-using existing volume with docker compose

Question

I have setup two standalone docker containers, one runs a webserver another one runs a mysql for it. Right now I was attempting to have it working with docker-compose. All is nice and it runs well, but I was wondering how could I re-use existing volumes from the existing standalone containers that I have previously created (since I want to retain the data from them).

I saw people suggesting to use external: true command for this, but could not get the right syntax so far.

Is external: true the correct way approach for this, or should I approach this differently? Or can I just specify the path to the volume within docker-compose.yml and make it use the old existing volume?

score 28 · Answer 1 · edited Oct 30 '21 at 03:05

Yes you can do it normally, just an example below: Set external to true and set name to the name of the volume you want to mount.

version: "3.5"
services:
  transmission:
    image: linuxserver/transmission
    container_name: transmission
    volumes:
      - transmission-config:/config
      - /path/to/downloads:/downloads
    ports:
      - 51413:51413
      - 51413:51413/udp
    networks:
      - rede
    restart: always

networks:
  rede:
    external: true
    name: rede
volumes:
  transmission-config:
    external: true
    name: transmission-config

score 11 · Accepted Answer · edited May 22 '23 at 15:17

11

Per the documentation, using the external flag allows you to use volumes created outside the scope of the docker-compose file.

However, it is advisable to create a fresh volume via the docker-compose file and copy the existing data from the old volumes to the new volumes

edited May 22 '23 at 15:17

SwDevMan81

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answered Feb 11 '20 at 03:32

Shenal Silva

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15

Why is it advisable to create a fresh volume? – FatFingersJackson Feb 26 '21 at 04:47
1

Documentation link should be: https://docs.docker.com/compose/compose-file/#external-1 – rumski20 Jun 21 '22 at 20:33

score 1 · Answer 3 · edited Nov 03 '22 at 19:37

You can create a volume explicitly using the docker volume create command, or Docker can create a volume during container or service creation. When you create a volume, it is stored within a directory on the Docker host. When you mount the volume into a container, this directory is what is mounted into the container.

If your system is running, you can exec into the mysql container, copy and move it outside.

docker cp "${container_id}":/path_to_folder /path_to_server

Re-using existing volume with docker compose

3 Answers3