Day 18 Task: Docker for DevOps Engineers

Docker Compose:

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

• With a YAML file, you define services, and with one command, you bring your environment to life or gracefully shut it down. Dive deeper into Docker Compose.

What is YAML?

• YML, often known as "yet another markup language," is the backbone of Docker Compose. It's a data serialization language that's both human-readable and easy to understand.

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

Task-1:

Learn how to use the docker-compose.yml file, to set up the environment, configure the services and links between different containers, and also to use environment variables in the docker-compose.yml file.

sample docker-compose file-

version: '3.3'

services:
  db:
    image: postgres
    container_name: postgres_db
    restart: always
    environment:
      POSTGRES_USER: user
      POSTGRES_PASSWORD: pass
      POSTGRES_DB: mydatabase

  web:
    image: nginx
    build: ./webapp
    depends_on:
      - db
    container_name: nginx_web
    restart: always
    ports:
      - "8080:80"

Task-2

• Pull a pre-existing Docker image from a public repository (e.g. Docker Hub) and run it on your local machine. Run the container as a non-root user (Hint- Use usermod command to give user permission to docker). Make sure you reboot instance after giving permission to user.

• SSH into the instance.

• Then update your packages using the command below:

sudo apt update

• Check if Docker is installed, if not, install it using the command below:

sudo apt update install docker.io

• As the user "ubuntu," running docker ps is not possible since it is a non-root user. To address this, the user was added to the "docker" group.

• However, docker ps is still not working because the server hasn't been rebooted after granting permission.

• Now, Docker commands can be run without sudo. Confirm the user's addition to the docker group using the command:

id

• This command provides details about the current user's UID, GID, and groups.

• Next, pull the Nginx image from the Docker registry (e.g., Docker Hub) and verify it using the command:

docker pull nginx
docker images

• Create a container from the Nginx image, perform port mapping in the same command to run the application on port 8000:

docker run -d -p 8000:80 --name nginx nginx:latest

• Open the security group and enable port 8000 for the Nginx server.

• Now, our Nginx server is running on port 8000.

• Inspect the container's running processes and exposed ports using the command:

docker inspect nginx

• Use the docker logs command to view the container's log output.

• we can use --tail=n (number of line) we want to see in log.

docker logs nginx 
docker log nginx --tail=50

• Use the docker stop and docker start commands to stop and start the container.

    docker stop nginx
    docker start nginx
  

• Use the docker rm command to remove the container when you're done.

    docker rm -f <cont-id> or <cont-name>
  

That's it for this Article.

Thank you for reading! 📘