Sharing a file between a persistent and a non persistent Docker Container

Question

I'm using Caprover with Docker to run a Django project (Django-Cookiecutter) which is non persistent. I'm also running a persistent app on the same server which imports csv data. I need the two apps to basically share a file together. This is how i imagined it:

1. The importer app imports csv data and stores it as a json file inside a specific folder.
2. The Django app accesses the json file in that folder and uses a script i wrote to import the json into the database. I'm struggling to understand how i can access the folder inside my importer app containing the json file from my django app. Does anyone have an idea on how i can make this happen between those two docker containers?

Answer 1

You can share a directory or file between the two containers by mounting the same directory in both containers. Here's a simple docker-compose example where two containers mount the same directory. Then the first container writes to a file and the second container reads from it.

Example

version: '3'

services:
  writer:
    image: alpine
    command:
      [
        "sh",
        "-c",
        "echo hello from writer >/shared-writer/hello.txt"
      ]
    volumes:
      - .:/shared-writer
  reader:
    image: alpine
    depends_on:
      - writer
    command: [ "cat", "/shared-reader/hello.txt" ]
    volumes:
      - .:/shared-reader

Notice:

• They both mount the current directory.
• The first container writes to a file inside the mounted volume.
• The second container reads from same file inside the mounted volume.
• The containers use different mount points (/shared-writer and /shared-reader) to demonstrate that the same directory from your host can be mounted in different locations in the containers.

Output

$ docker-compose up
Starting shared-mount-example_writer_1 ... done
Starting shared-mount-example_reader_1 ... done
Attaching to shared-mount-example_writer_1, shared-mount-example_reader_1
reader_1  | hello from writer
shared-mount-example_writer_1 exited with code 0
shared-mount-example_reader_1 exited with code 0