Docker for Devops Engineer

Docker Volume

A Docker volume is a way to persist data in Docker containers beyond the lifecycle of a single container.
When you run a container, it runs in isolation and any data created and modified within the container is typically lost when the container is stopped or removed.
Docker volumes provide a mechanism for storing and sharing data between containers, as well as between containers and host systems.

Docker Networks

Docker allows you to create a virtual space called networks, where you can connect multiple containers (small packages that hold all the necessary files that hold all the necessary files for a specific application to run). This way, the containers can communicate with each other, and also with the host machine(the computer on which Docker is installed).
When we create 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 )

  So, here we use the docker-compose up command with the -d flag to start a multi-container application in detached mode.

  

• Use the docker-compose scale command to increase or decrease the number of replicas for a specific service. You can also add replicas in deployment file for auto-scaling.

  

• 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.

  1. Create a docker volume:- You can create a Docker volume using 'docker volume create' command.

     

  2. Mount the volume in a container:- When you run a container, you can mount the volume by specifying it with the '-v' or '--volume'.

     

  3. Use the Volume:- Any data that is written to the /app/data within the container will be stored inside 'mydata' volume on the host. This data will persist even if the container is stopped or removed.

  4. Sharing volumes:- You can use the same volume among multiple containers by specifying the same volume name when starting the container. They will all have access to same data.

  5. Remove Volumes:- To remove a Docker volume, use 'docker volume rm' command.

     

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

     To create two or more containers that read and write data to the same volume using the docker run --mount command, you can follow these steps:

     1. Create a docker volume

        

     2. Run containers with Shared volume
        In this example:

        • --name specifies the name for each container (container1 and container2).

        • --mount is used to mount the mydata volume into the /app/data directory inside each container.

        • mysql is the Docker image you want to run.

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