The problem is rather contrived so the solution is rarely needed. But if you'll ever find yourself in this situation apparently it's easy to get out. 😃

Suppose you want to run the same docker-compose with the same Dockerfile but from several subfolders and you don't like duplication. So you fave a folder structure like this:

project
  |- subproject1
    |- the_file.txt
  |- subproject2
    |- the_file.txt
  |- Dockerfile
  |- compose.yml

Now you'd like to run docker-compose -f ../compose.yml up from each of subproject1 and subproject2 and for docker-compose to set the context for the Dockerfile to each of the folders respectively.

You do it with $PWD as follows:

version: "3.9"
services:
  assignment:
    build:
      context: $PWD
      dockerfile: ../Dockerfile
    ports:
      - "8080:8080"
    depends_on:
      - "database"
  database:
    image: "mariadb:10.5"
    restart: "always"
    environment:
      MYSQL_ROOT_PASSWORD: "secret_pass"

in the compose.yml file. For the sake of argument we pretend we need a separate service with a database in each case.

Then you write your Dockerfile as usual:

FROM node:15

# Create app directory
WORKDIR /app

RUN npm install -g http-server

# Bundle app source
COPY . .

EXPOSE 8080
CMD [ "http-server", "-p", "8080" ]

And now for the subproject1 you should have the first text file exposed over the Web interface, and for the subproject2 the second text file.

Yep, as I told you from the start this is rarely needed because you rarely have two (or more) subprojects built with exactly the same Dockerfile. In the end it turned out I myself don't need this setup. But I spent surprisingly long time figuring (Googling) out the right config, so we all have it now laid out in the case we ever need it. 😃