Docker Images vs Docker Containers

ISO image and Docker image

ISO image file is a static file, when we install it to a Computer/Laptop, all the softwares/applications in the iso package will run lively when the system is powered on.

Similarly, Docker Image is a static package, when we create a container using that image, the applications packaged in the docker image will be running live inside docker container

Server-detail

Similar like downloading the ubuntu iso file from official ubuntu website.

All the docker images are stored in docker registry Docker Hub https://hub.docker.com

Pulling the docker image from Docker hub

Lets check what are the images present in the server.

azureuser@raghav:~$ docker image ls
REPOSITORY   TAG       IMAGE ID   CREATED   SIZE

No docker images are present in the server.

Lets pull the ubuntu docker image from docker hub

Docker image follows the format DOCKER_IMAGE_NAME:TAG

By default if you are not passing the tag, it will pull the latest tag

azureuser@raghav:~$ docker pull ubuntu
Using default tag: latest
latest: Pulling from library/ubuntu
6b851dcae6ca: Pull complete 
Digest: sha256:6120be6a2b7ce665d0cbddc3ce6eae60fe94637c6a66985312d1f02f63cc0bcd
Status: Downloaded newer image for ubuntu:latest
docker.io/library/ubuntu:latest

Now check the docker images in server

azureuser@raghav:~$ docker images
REPOSITORY   TAG       IMAGE ID       CREATED       SIZE
ubuntu       latest    99284ca6cea0   2 weeks ago   77.8MB

Docker image with tag latest is pulled from the Docker hub.

Lets pull ubuntu docker image with tag 23.10

azureuser@raghav:~$ docker pull ubuntu:23.10
23.10: Pulling from library/ubuntu
a3cc0ea50b9a: Pull complete 
Digest: sha256:bd1e0eb3171a6e499c84211e73c4f5f5b2a585507256f772f5c4f4420a3d8591
Status: Downloaded newer image for ubuntu:23.10
docker.io/library/ubuntu:23.10

azureuser@raghav:~$ docker images
REPOSITORY   TAG       IMAGE ID       CREATED       SIZE
ubuntu       23.10     ce0fd6ed554b   2 weeks ago   70.4MB
ubuntu       latest    99284ca6cea0   2 weeks ago   77.8MB

Now we have two ubuntu docker images in server, one with tag latest and another with tag 23.10

Creating docker container using docker image

Lets create a docker container with image ubuntu:23.10

azureuser@raghav:~$ docker run -it ubuntu:23.10 bash
root@fc9a74dbecbf:/# pwd
/
root@fc9a74dbecbf:/# ls
bin  boot  dev  etc  home  lib  lib32  lib64  libx32  media  mnt  opt  proc  root  run  sbin  srv  sys  tmp  usr  var
root@fc9a74dbecbf:/# id
uid=0(root) gid=0(root) groups=0(root)
root@fc9a74dbecbf:/# cat /etc/os-release 
PRETTY_NAME="Ubuntu Mantic Minotaur (development branch)"
NAME="Ubuntu"
VERSION_ID="23.10"
VERSION="23.10 (Mantic Minotaur)"
VERSION_CODENAME=mantic
ID=ubuntu
ID_LIKE=debian
HOME_URL="https://www.ubuntu.com/"
SUPPORT_URL="https://help.ubuntu.com/"
BUG_REPORT_URL="https://bugs.launchpad.net/ubuntu/"
PRIVACY_POLICY_URL="https://www.ubuntu.com/legal/terms-and-policies/privacy-policy"
UBUNTU_CODENAME=mantic
LOGO=ubuntu-logo