(Day 13) Task : Docker Volumes & Sharing :-

Introduction :-

Containers are designed to be ephemeral, meaning their file systems are wiped clean when a container stops. But what if we want to persist data or share data between containers? That’s where Docker Volumes come in.

In this note, you’ll learn:

• What Docker Volumes are.

• How to create and use them.

• How to share volumes between containers.

• Volume types and their use cases.

What is a Docker Volume?

• A Docker Volume is a persistent storage mechanism managed by Docker. It stores data outside of the container's file system (outside of the union file system), making it ideal for preserving data between container runs.

• Think of volumes as mount points into containers, backed by a specific location on the host machine.

• Volume is a directory inside our container Firstly, we have to declare the directory as a volume Even if we Stop Container , Still we can access Container.

• Volume will be Created in one Container and then Shared to multiple Containers Anyone From Any Container can Send Data and Everyone can see it.

• You can declare a directory as a volume only while creating Container.

• You Can’t Create Volume From Existing Container , Volume won’t be included when you update an image.

Why Use Docker Volumes?

• Data Persistence: Keeps your data safe across container restarts or rebuilds.

• Decoupling: Separates data from application code.

• Sharing: Allows multiple containers to read/write to the same data.

• Performance: More efficient than using bind mounts for heavy workloads.

• Backups: Easy to backup and restore.

Benefits Of Volume :-

• Decoupling Container from Storage.

• Share Volume among Multiple Containers.

• Attach Volume to Container.

• On Deleting Container Volume Doesn’t Delete.

Volume Mapping or Sharing :-

i) Container to Container :

It means two or more containers access the same volume, enabling them to read/write shared data. This is commonly used for:

• Sharing configuration.

• Logging between services.

• Data exchange without external networks.

Create Volume From DockerFile :

• Create a Docker file using vi editor :

vi Dockerfile

• Open vi editor and make a volume inside it :

# After Opening Vi Editor write below codes
FROM ubuntu
VOLUME ["/MY VOLUME1"]

• Create Image From DockerFile :

docker build -t myimage .

• Create Container From Image and Run it :

docker run -it --name container1 myimage /bin/bash

• Share Volume with Another Container :

docker run -it --name container2 --privileged=true --volumes-from container1 ubuntu /bin/bash

• Now after creating container2 Myvolume1 is visible, whatever we do in one volume , can see from other volume :

touch filex filey
docker start container1
docker attach container1
cd Myvolume1
ls
exit

Create Volume By Using Commands :

• Made Container Along with Volume :

docker run -it --name container3 -v/volume2 ubuntu /bin/bash
ls
cd volume2
touch file1 file2
exit

• Now Create one more container and Share Volume 2 :

docker run -it --name container4 --privileged=true --volumes-from Container3 ubuntu /bin/bash

• Now after creating container3 volume2 is visible, whatever we do in one volume , can be seen from other volume inside another container :

cd volume2
ls
touch file4 file5
exit
docker start container3
docker attach container3
cd volume2
ls

Basic Commands For Volume Locally :

1. Docker volume create <Volumename>.

Purpose: Creates a named Docker volume.

docker volume create myvol

This volume is now available for use by any container.

It will be stored in Docker’s default volume directory:

2. Docker volume ls :

Purpose: Lists all volumes managed by Docker.

docker volume ls

3. Docker volume inspect <Volumename>.

Purpose: Shows detailed metadata about the volume.

docker volume inspect myvol

4. Docker volume rm <Volumename>.

Purpose: Deletes a specific volume, but only if it’s not in use by a container.

docker volume rm myvol

5. Docker volume prune :

Purpose: Deletes all unused volumes.

docker volume prune