🚢Day 19 - Exploring Docker Volume & Docker Network

Docker-Volume

Docker allows you to create something called volumes. Volumes are stored outside the container's filesystem, which allows them to persist even if the container is stopped or deleted. You can also mount from the same volume and create more containers having same data.

You can create a volume using the docker volume create command:

docker volume create vol

Docker Network

A docker network is like a virtual bridge that allows Docker containers to communicate with each other and with the outside world. It provides a way for containers to Communicate to each other, even if they are running on different machines or hosts there are total 7 network type through which we can communicate.

Task-1: Create a multi-container docker-compose file which will bring UP and bring DOWN containers in a single shot

It's simple example of a multi-container Docker Compose file that includes an application and a database container. This example uses Two-tier flask Application with MYSQL database.

version: '3'

services:
  web:
    image: python:3.9-slim
    volumes:
      - mysql-data: /var/lib/mysql
      - .message.sql: /docker-entrypoint-initdb.d/message.sql
    working_dir: /app
    command: ["python", "app.py"]
    ports:
      - "5000:5000"
    depends_on:
      - mysql

  mysql:
    image: MYSQL:5.7
    environment:
      MYSQL_HOST: mysql
      MYSQL_USER: root
      MYSQL_PASSWORD: test@123
    ports:
      - "3306:3306"

To bring up the containers, run:

docker-compose up -d

To bring down the containers, run:

docker-compose down

This will stop and remove all containers, networks, and volumes associated with the application.

Task-2: Learn how to use Docker Volumes and Named Volumes to share files and directories between multiple containers.

First we'll create two containers that read and write data to the same volume.

docker volume create shared_data

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

  Container 1:

    docker run -d --name container1 --mount source=shared_data,target=/data busybox sh -c "echo 'Data from Container 1' > /data/file.txt && tail -f /dev/null"
  

  This command runs the first container named container1, mounting the shared_data volume to the /data directory inside the container. It writes data to a file named file.txt within the volume.

  Container 2:

    docker run -d --name container2 --mount source=shared_data,target=/data busybox sh -c "echo 'Data from Container 2' > /data/file2.txt && tail -f /dev/null"
  

  Similarly, this command runs the second container named container2, also mounting the shared_data volume to the /data directory inside the container. It writes different data to another file named file2.txt within the same volume.

Now you have two containers (container1 and container2) both reading and writing data to the same volume (shared_data). Any changes made by one container will be visible to the other container, as they are sharing the same volume.

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

To verify that the data is the same in all containers, you can use the docker exec command to run commands inside each container and check the content of the shared volume. Here's how you can do it:

1. Verify Data in Container 1:

    docker exec container1 cat /data/file.txt

This command will output the content of file.txt in container1

• 2. Verify Data in Container 2:

    docker exec container2 cat /data/file.txt
  

  Similarly, this command will output the content of file.txt in container2.

• 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 command to list all volumes and then the docker volume rm command to remove the specific volume. Here's how:

  List all volumes

    docker volume ls
  

  This command will list all Docker volumes present on your system, including the shared_data volume we created earlier.

Remove the volume:

docker volume rm shared_data

This command will remove the shared_data volume. Make sure you are not actively using this volume in any running containers, as removing the volume will delete all data stored within it.

Conclusion

In above task, we have learned to use Docker Volumes and Named Volumes to share files and directories between multiple containers. We created a Docker volume named shared_data, wrote data to a file inside the volume from one container, and then read the same file from another container. This demonstrates how Docker Volumes can be used to share data between containers, allowing them to access and modify the same files.

😊Happy Learning : )