Docker Docker Docker Compose What is Docker Compose MultiContainer Orchestration for DevTest

1. Core Command / Concept

Docker Compose allows you to define and run multi-container applications with a single command. docker-compose up

2. Step-by-Step

1. Create a new directory for your project and navigate to it: mkdir myproject && cd myproject
2. Create a new file named docker-compose.yml with the following content:

version: '3'
services:
  web:
    build: .
    ports:
      - "8080:80"

1. Run docker-compose up to start the containers: docker-compose up
2. Check the containers are running: docker ps
3. ⚠️ Stop all containers: docker-compose stop
4. Remove all containers: docker-compose rm
5. Remove the Docker network: docker network rm myproject_default
6. Remove the Docker volume: docker volume rm myproject_default

3. Real Commands with Examples

Example 1: Running a simple web server

Purpose: Run a simple web server using the official Python image.
Command: docker-compose up -d --build Flags: - -d runs the containers in detached mode.
- --build builds the Docker image from the current directory.

Example 2: Running a database and web server

Purpose: Run a PostgreSQL database and a web server using the official Python image.
Command: docker-compose up -d Flags: - -d runs the containers in detached mode.

Example 3: Running a web server with environment variables

Purpose: Run a web server using the official Python image with environment variables.
Command: docker-compose up -d --env-file .env Flags: - --env-file loads environment variables from a file.

4. Common Errors

Error 1: Image not found

Error message: ERROR: Service 'web' uses an image, but 'docker-compose config' indicates support for Docker Compose files. Why it happens: The image is not defined in the docker-compose.yml file.
One-line fix: docker-compose config to check the configuration.

Error 2: Port already in use

Error message: Error response from daemon: Ports are not available: listen tcp 0.0.0.0:8080: bind: address already in use Why it happens: The port is already in use by another process.
One-line fix: docker-compose stop to stop the container.

Error 3: Volume not found

Error message: ERROR: The container name "/myproject_web_1" is already in use by container "/myproject_web_1". Why it happens: The volume is already in use by another container.
One-line fix: docker-compose rm to remove the container.

5. Quick Checks

Scenario 1: Check if a container is running

Situation: You want to check if a container is running.
Command: docker ps What a correct response looks like: CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES

Scenario 2: Check the logs of a container

Situation: You want to check the logs of a container.
Command: docker-compose logs -f What a correct response looks like: The logs of the container.

Scenario 3: Check the status of a service

Situation: You want to check the status of a service.
Command: docker-compose ps What a correct response looks like: The status of the service.

6. Last-Minute Reference

• docker-compose up starts the containers.
• docker-compose down stops and removes the containers.
• docker-compose restart restarts the containers.
• docker-compose stop stops the containers.
• docker-compose rm removes the containers.
• docker-compose config checks the configuration.
• docker-compose logs checks the logs.
• docker-compose ps checks the status of the services.
• docker-compose exec runs a command in a container.
• docker-compose run runs a command in a new container.
• ⚠️ docker-compose rm -f removes all containers without prompting.
• ⚠️ docker-compose down -v removes all volumes without prompting.
• ⚠️ docker-compose stop --time=1 stops the containers with a 1-second timeout.