Command substitution in docker-compose.yml when scaling a service with multiple instances

Question

The docker-compose.yml file I am using is following:

services:
  web:
    image: nginx:stable-alpine
    ports:
      - "8080-8130:80"
    volumes:
      - ${TEMPDIR}:/run

I launch 20 containers with the following command:

TEMPDIR=`mktemp -d` docker-compose up -d --scale web=20

All of the containers launch ok, but they all have the same temp volume mounted at /run, whereas I need each running container to have a unique temp volume. I understand that the problem is that the above yml file is doing Variable Substitution whereas what I need is Command Substitution but I could not find any way of doing that in the official reference , especially when launching multiple instances of the same docker image. Is there some way to fix this problem?

Answer 1

Maybe what you are looking for is tmpfs .

Mount a temporary file system inside the container. Can be a single value or a list.

You can use it simply like this

services:
  web:
    image: nginx:stable-alpine
    ports:
      - "8080-8130:80"
    tmpfs: /run

Here are the references:

• tmpfs on Docker
• tmpfs on Docker compose