Docker-Volume

Docker allows you to create something called volumes. Volumes are like separate storage areas that can be accessed by containers. They allow you to store data, like a database, outside the container, so it doesn't get deleted when the container is deleted. You can also mount from the same volume and create more containers having same data.

Docker Network

Docker allows you to create virtual spaces called networks, where you can connect multiple containers (small packages that hold all the necessary files for a specific application to run) together. This way, the containers can communicate with each other and with the host machine (the computer on which the Docker is installed). When we run a container, it has its own storage space that is only accessible by that specific container. If we want to share that storage space with other containers, we can't do that.

Task-1

Create a multi-container docker-compose file which will bring UP and bring DOWN containers in a single shot ( Example - Create application and database container )

Use the docker-compose up command with the -d flag to start a multi-container application in detached mode.

For this lets clone the code of an app from Github first

For that, copy the link of repo from GitHub:

In our Linux machine, use command

git clone <repo link>

The repo is now cloned on local machine

cd django-todo-cicd

Since, we are creating a docker-compose file from scratch, deleting the docker-compose.yml file.

Now lets create a docker-compose.yaml file from scratch

vim docker-compose.yaml

Now write the following code:

version : "3.3"
services :
  my_web_app:
    container_name: "django-todo-app"
    build: .
    ports:
      - 8000:8000
    volumes:
      - django-todo-volume:/app
  my_db:
    container_name: "django-mysql-db"
    image: mysql:5.7
    ports:
      - 3306:3306
    environment:
      MYSQL_ROOT_PASSWORD: "test@123"
volumes:
  django-todo-volume:

Now use command:

docker-compose up -d

Use the docker-compose ps command to view the status of all containers, and docker-compose logs to view the logs of a specific service.

Now check whether container is running using docker-compose ps

Thus multiple containers are now created using a single docker compose file

Use docker-compose logs to check the logs

Use the docker-compose down command to stop and remove all containers, networks, and volumes associated with the application

Now, to stop the containers, use command

docker-compose down

To check whether they are stopped use command

docker ps

The containers are now stopped.

Task-2

Learn how to use Docker Volumes and Named Volumes to share files and directories between multiple containers.

Create a diectory for volumes using

mkdir volumes

Now create a docker volume using

sudo docker volume create my_volume

Inspect the volume using

docker volume inspect my_volume

Create two or more containers that read and write data to the same volume using the docker run --mount command.

sudo docker run -d -p 8000:8000 --mount source=my_volume,target=/app django-todo-app:latest

sudo docker run -d -p 8001:8001 --mount source=my_volume,target=/app django-todo-cicd_my_web_app:latest

Verify that the data is the same in all containers by using the docker exec command to run commands inside each container.

docker exec -it <cont id> sh

Use the docker volume ls command to list all volumes and docker volume rm command to remove the volume when you're done.

docker volume ls

To remove volume

docker volume rm my_volume

If it returns error saying volume in use, enter command:

docker container prune

Now try to remove volume