Docker Volumes: With Real-Time Examples

While working with docker, I observed that these are the 4 pillars for docker [Images, Containers, Volumes and Networks], In this blog we are going to discuss about Docker volumes. Docker volumes are the preferred way to persist data generated by and used by Docker containers. In this blog, we'll break down the anatomy of Docker volumes and demonstrate their use with practical, real-world examples.

What Are Docker Volumes?

Docker Volume is a mechanism that helps us to store data outside the container. They prevent data loss when your container stops. You can easily connect the volume to a new container, and your data from the previous one will carry over to the new container.

When a container writes data, it typically writes to its writable layer. However, this data is temporary and will be lost when the container is stopped or removed. To avoid this, Docker allows you to mount a volume to a specific directory in the container's file system. If any data we write inside the container, it automatically stores the data on volume. So the data will present even the container is deleted.

To better understand this, think of containers as whiteboards used during meetings. When the meeting ends (the container stops), the whiteboard is wiped clean (data is lost). A Docker volume is like a notebook where all important notes (data) are stored securely, ready to be referenced even after the meeting.

Production Issues:

In production, we usually maintain multiple containers for a single service, its hard to maintain the configurations upto date for all containers. Docker volume helps us to share the data between multiple containers. If we update the data on one container, it will replicate to all the containers.

Common commands in volumes:

To create a volume:

docker volume create volume-name

To see the list of volumes:

docker volume ls

To see the full details about volume:

docker volume inspect volume-name

To delete a volume:

docker volume rm volume-name

NOTE: We can’t remove the volumes which are attached to containers. It should be free from container.

To delete multiple volumes:

docker volume rm volume-name volume-name volume-name

To delete unused volumes:

docker volume prune

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Practical implementation of volumes:

Lets create a volume and mount it to container:

docker volume create swiggy

Now i have created a swiggy volume

To inspect the volume:

[root@ip-172-31-13-80 ~] docker volume inspect swiggy
[
    {
        "CreatedAt": "2025-01-25T08:17:45Z",
        "Driver": "local",
        "Labels": null,
        "Mountpoint": "/var/lib/docker/volumes/swiggy/_data",
        "Name": "swiggy",
        "Options": null,
        "Scope": "local"
    }
]

Now we can see the mountpoint: /var/lib/docker/volumes/swiggy/_data

Lets mount it to container:

docker run -itd --name cont1 --mount src=swiggy,destination=/myapp ubuntu

Now the container will be created, inside the container /myapp folder will be there. Lets go to container check it.

Go to container:

docker exec -it cont1 bash

Now we will enter into the container, we can see myapp folder is there.

Lets add some files and folders inside the myapp folder

cd myapp
touch file{1..4}
mkdir devops{1..3}
ls

Now exit from the container and check the swiggy volume, the data is present on volume.

Go to volume path

cd /var/lib/docker/volumes/swiggy/_data/

now check the files:

Even if we add some files here, then the data will replicate inside the container.

Now lets go to container1 and check the files present in myapp folder.

NOTE: So we can clearly observe that the data is replicated between container to host. we can mount our volumes to multiple containers to replicate the same process.

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Host to Container:

Bind mounts have been part of Docker since the beginning. They help us to link a file or folder from our Docker host to the container’s file system. If the file or folder doesn’t already exist in the container, Docker will create it automatically when we start the container. Any changes you make to that file or folder on our Docker host will show up in the container, and any changes made inside the container will show up on our Docker host.

However, this can create security risks. For example, if something inside the container changes a file, that change will also affect the file on our Host. So, you need to be careful when using bind mounts.

Bind mounts are especially useful during development. You can link your code folder to the container, so when you update your code, the changes will appear in the container immediately. This saves time since you don’t have to rebuild the image every time you make a change.

Practical implementation of Bind mounts:

lets create a folder in Dockerhost

mkdir zomato && cd zomato

now create some files

touch index.html app.py style.css requirements.txt

Now lets create the container inside the same directory:

docker run -itd --name cont2 -v "$(pwd)":/appcode ubuntu

Now lets get into the container and check the same files

docker exec -it cont2 bash
cd appcode

Now lets create some files inside the container, that will replicate in Dockerhost on the same zomato folder

now lets exit from container and check in docker host

So here also the data is replicated on between host to container. We can create multiple containers from same path to replicate the data to containers.

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In the above 2 models, we observed that data replication is like a 2 way [host to container, container to host]. This can create security risks. For example, if something inside the container changes a file, that change will also affect the file on our Host. So, we need to restrict by preventing the changes on container we need to create readonly volumes.

Read Only Volumes

We can make a volume read-only so that the container can read from that volume and can not write. It can be used if you have any security concerns depending upon the requirement of the application. These volumes will create while creating the container only

command to create a container with read only volume:

docker run -itd --name mustafa -v uber:/app:ro ubuntu

In the above command, uber is the volume that will created on host, and /app is the path where we mounted inside the container. ro represents the readonly volume.

Now lets enter into the container and add some data on /app folder, we will get permission denied error.

docker exec -it mustafa bash
cd app

see, we cant write the data from container, but if we write the data on uber volume in docker host, it will replicate here.

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Sharing the volumes from container-container

we can share the volume from one container to another container while creating.

docker run -itd --name devops --privileged=true --volumes-from=mustafa ubuntu

In the above command, we can see the volumes from mustafa container is going to share with devops container.

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Creating a volume using Dockerfile

Not only with the commands, we can also create the docker volumes with Dockerfile

FROM ubuntu
VOLUME [/mycode]

If we build the above Dockerfile and run the image, automatically a container and a random volume will be created. Now the volume will present inside the volume, when ever we run the image, automatically this volume will creates.

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Examples of docker volumes

Example-1:

• create a volume

    docker volume create paytm
  

• go to that volume path

    /var/lib/docker/volumes/paytm/_data/
  

• add some code in that volume

  

• Now lets create a container by mounting the volume

    docker run -itd --name freelancer -p 1234:80 --mount src=paytm,destination=/usr/local/apache2/htdocs/ httpd
  

• Now lets access the application using 1234 port

  

  We can share this volume to any container.

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Example-2:

• Create a folder on Docker host

    mkdir testapp && cd testapp
  

• Keep the code inside the folder

  

• Now create a container from the same folder

    docker run -itd --name cont99 -p 1122:80 -v "$(pwd)":/usr/share/nginx/html/ nginx
  

Now lets access the application using 1122 port

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Example-3:

We can directly create a container and volume first

docker run -itd --name app-container -p 2233:80 -v mydata:/usr/share/nginx/html nginx

If we access the app using 2233 port, we will get only nginx page

Lets add the data on mydata volume

cd /var/lib/docker/volumes/mydata/_data/

make some modifications on index.html file and refresh the browser

Conclusion

Hope you found this blog helpful. I have tried to cover all the basics about volume or mount you need to know as beginners. There are many more things about this topic that I will cover in future blogs.

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