Docker Volume

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Data available even though container got deleted

Why do we need to have docker volume?

Data no longer available once container is stopped or removed

Docker container did not persist data permanently

Different types of Volume Mounts

Volume Mount and Bind Mount

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Containers are usually immutable and ephemeral

Immuntable Infra: Only re-deploy container and never change

This is the ideal scenario: What about DB or configuration related info

Docker gives us features to ensure these "seperation of concerns"

This is called "Persistent Data"

Volume Mount

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Volumes are created at Host File system and managed by Docker

Make special location outside of the container

At RHEL Linux or Ubuntu, volumes are located at /var/lib/docker/volumes/

Volumes can be created by two way

1) docker volume create

2) Run time

Volume can be mounted to multiple containers

Volume can not be removed

Volume can be removed by docker volume prune command

Usage of the Volumes

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1) Sharing data among various containers

2) When you want to backup, restore, or migrate data amoung multiple hosts

Bind Mount

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Directory can be available anywhere in the Docker host system

Link container path to host path

(Maps a host file or directory to a container file or directory)

- Changes can be incorporated at host files and container files

- There is a sync between host and container and vice versa

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Lab

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Listing Docker volume

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docker volume ls

Creating a Volume

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docker volume create --name customerdb

docker volume ls

Use Case 1: Creating a container with volume and remove the container once you exit from the container

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docker run -it --name suse1 --rm -v customerdb:/platniumcustomer centos

- suse1 : Name of the container

- -v: Volume

- Platniumcustomer : Creating a folder at Container OS

- --rm indicating that once you exit from container and automatically remove the container

Output is

You are getting into container OS and apply ls -la command

You get one folder of "platniumcustomer"

Apply command for Mount

df -h

which list out all mount details and you can get platniumcustomer

Get into platniumcustomer folder and add few files under this folder

After created files, apply below

exit

You are now Base os and exit from container os

Since, you apply --rm commands container get deleted automatically

You can get to know after apply below

docker ps

and

docker ps -a

docker volume inspect customerdb

You can get output of Json format and refer Mount Point Path

Go to Mount Point path where you get the file which you created inside the container

Lesson Learned: Even if you deleted container, data can be alive at base machine

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Use Case 2: Creating a new container with same volume

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docker run -it --name suse2 --rm -v customerdb:/platniumcustomer1 centos

Created automatically folder of platniumcustomer1 and file which you created earlier container

of suse1

Old container deleted, but container data stored in the Host machine volume

Host machine volume bind with new container of suse2

CREATING A VOLUME THAT PERSISTS WHEN THE CONTAINER GOT DELETED

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Use Case 3: Creating a volume dynamically (During run time)

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docker run -it --name suse3 -v customerdb1:/regularcustomer centos

You are now at container os of centos

Go to regularcustomer folder and create a new file

After created the file, apply CTRL pq from the container

(Now whatever data I captured here that persists to host machine too and if I remove the container,

the same data persists to host machine)

Now container alive now since we did not use --rm command

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Use Case 4: Container Data Persists after stop the container

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Data can be alive, after stop the container

Apply

docker stop <container name or id>

Data can be persits, even after stop the container

docker start <container name or id>

Get into container OS as per below

container exec -it < Container id> bash

Get into container os and you go respective foler where you can get respective files

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Use Case 5: Creating Volume from an existing directory with data

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docker run -it --rm --name suse4 -v customerdb2:/var centos

Get into container os and system created var directory automatically

exit from container os

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Use Case 6: Linking data with other container

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docker run -it --rm --name suse5 -v customerdb2:/linkcustomer centos ls linkcustomer

Above command is for displaying ls commnad, that is going to display contents of the volume

without get into bash termainals

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Use Case 7: Data sharing between containers

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docker run -it --name suse6 -v customerdb3:/sharecustomer centos

You are now at container os and get into sharecustomer folder

At sharecustomer folder, you create a few files and save it

Exit from container os

Use Case 8 : Create suse7 container and mount volumes from suse6

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docker run -it --name suse7 --volumes-from suse6 centos

Get into sharecustomer folder where you get the data

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Use Case 9: Bind Volume

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docker run -it --name suse8 -v /hostvolume/iosmobile:/containervolume/iosmobile centos

Now, you are in the container

Get into containervolume/iosmobile directory and create few files

After exit from the container, at host system you can get data which created at container

At host system, edit the files (Whatever you edited which can be available at container too)

You log into container and go to respective file and check it