Day 18 Task: Docker for DevOps EngineersDocker Compose

Docker Compose

• Docker Compose is a tool that was developed to help define and share multi-container applications.

• With Compose, we can create a YAML file to define the services and with a single command, can spin everything up or tear it all down.

What is YAML?

• YAML is a data serialization language that is often used for writing configuration files. Depending on whom you ask, YAML stands for yet another markup language or YAML ain’t markup language (a recursive acronym), which emphasizes that YAML is for data, not documents.

• YAML is a popular programming language because it is human-readable and easy to understand.

• YAML files use a .yml or .yaml extension.

• ompose.yml). This file specifies the services, networks, and volumes required for your application. Here is a basic example:

    yamlCopy codeversion: '3'
    services:
      web:
        image: nginx:latest
        ports:
          - "8080:80"
      db:
        image: postgres:latest
        environment:
          POSTGRES_DB: mydatabase
          POSTGRES_USER: user
          POSTGRES_PASSWORD: password
  

  In this example, two services (web and db) are defined. The web service uses the latest Nginx image and maps port 8080 on the host to port 80 on the container. The db service uses the latest PostgreSQL image and sets environment variables for database configuration.

  You can run this application with:

    bashCopy codedocker-compose up
  

  And stop it with:

    bashCopy codedocker-compose down
  

  Task-2: Working with Docker Compose and Existing Images

  1. Pull a Docker Image:

     You can pull an image from Docker Hub using docker-compose.yml. Add a services section for the image you want to use and define its configuration. Example:

      yamlCopy codeversion: '3'
      services:
        web:
          image: nginx:latest
          ports:
            - "8080:80"
     

     Run it with:

      bashCopy codedocker-compose up
     

  2. Run as Non-Root User:

     To run Docker commands without sudo, ensure your user is added to the docker group:

      bashCopy codesudo usermod -aG docker $USER
     

     After making this change, you need to reboot your machine for the changes to take effect.

  3. Inspect Running Processes and Exposed Ports:

     Use docker ps to see running containers and docker inspect for detailed information:

      bashCopy codedocker ps
      docker inspect <container_id>
     

  4. View Container Logs:

     You can view logs using docker logs:

      bashCopy codedocker logs <container_id>
     

  5. Stop and Start Container:

      bashCopy codedocker-compose stop
      docker-compose start
     

  6. Remove Container:

      bashCopy codedocker-compose down
     

     If you want to remove the image as well:

      bashCopy codedocker-compose down --volumes
     

Remember to replace <container_id> with the actual container ID.