Day 19 Task: Docker for DevOps Engineers

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 the same data.

For more understanding of Docker volume read my article: Understanding Docker volume

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). 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.

For more understanding of the docker network read my article: Understanding docker Network

Task-1

Create a multi-container docker-compose file that will bring UP and bring DOWN containers in a single shot ( Example - Create application and database container ). Clone the repository https://github.com/Parimal-Pradhan/django-todo-cicd.git Thank you Shubham sir.
Note: 1. Docker Should be installed on your machine.

2. Create a user once the docker is installed otherwise you will need to use sudo every time. (command creates user and group: sudo usermod - aG docker $USER)

3. Install docker-compose (sudo apt install docker-compose).

Use the docker-compose up command with the -d flag to start a multi-container application in detached mode.
```
  ubuntu@ip-172-31-93-214:~/django-todo-cicd$ sudo docker-compose up -d
```
Use the docker-compose scale command to increase or decrease the number of replicas for a specific service. You can also add replicas in the deployment file for auto-scaling.
```
  docker-compose up -d --scale web_server=3
```
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.
Use the docker-compose down command to 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.

Let's create volume first. To create volume in docker we need to use docker volume create command and to see the list of docker volume we need to use docker volume ls command.

docker volume create my_app_data
docker volume ls

So we have created volume my_app_data now our next task is to attach it while creating containers.

Create two or more containers that read and write data to the same volume using the docker run --mount command.
```
  docker run -d --name cont2 --mount source=my_app_data,target=/app_data nginx: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 972a6496d0a1 /bin/bash
  ls
```
Use ctrl+p followed by ctrl+q to come out of the container without the existing container.
Use the docker volume ls command to list all volumes and the docker volume rm command to remove the volume when you're done.
```
  docker volume rm my_app_data
  docker volume ls
```