context or workdir for docker-compose

I think you're looking for working_dir. Search for "working_dir" in the docker-compose reference.

You can specify the working directory as follows.

version: '2'
services:
  test:
    build:
      context:    /path/to/source/dir/
      dockerfile: /path/to/custom-Dockerfile/relative/tocontextdir/Dockerfile
    working_dir: /app