How to read / understand a docker-compose.yml and what the "stdin_open: true tty: true" components do?

Question

Taking a course that deals with these; the actual specifics is not pertinent to the course, but I generally have interest in trying to understand things regardless.

I have a docker-compose.yml file which I 'call on', or 'spin up'. The file contains the following information:

services:
  redis:
    image: redis:latest
    expose:
      - "6379"

  sample0395:
    image: sample0395/base:latest
    stdin_open: true
    tty: true
    expose:
      - "8888"
    ports:
      - "8888:8888"

From what I understand, and just based on the hierarchy as shown:

• redis and sample0395 are 'services'
• redis:latest and sample0395/base:latest are the image_name:tag combinations
• expose and ports: list the ports (not sure what the difference is or what the significance is of the difference between these two)
• I have no idea what stdin_open or tty do, and cannot seem to get an understanding through google.

Answer 1

tty and stdin_open are analogous to the -t and -i arguments for the docker run command, respectively.

You use stdin_open when you need to work on a project outside the Docker container.

You use tty when you need to work on a project inside the Docker container.

To test this out, try running docker-compose up with either tty or stdin_open but not both and you'll find that with stdin_open you don't log in to the container's terminal while the opposite happens with tty.

As for your question regarding the difference between expose and ports, answers are found here.