What is Docker Images?

Pre-requisite: Introduction to Docker

Docker Image is an executable package of software that includes everything needed to run an application. This image informs how a container should instantiate, determining which software components will run and how. Docker Container is a virtual environment that bundles application code with all the dependencies required to run the application. The application runs quickly and reliably from one computing environment to another.

Running Instances from DockerFile

Running Containers from Docker Image:

Follow the below steps to create a Docker Image and run a Container:

Step 1: Create a Dockerfile.

Step 2: Run the following command in the terminal and it will create a docker image of the application and download all the necessary dependencies needed for the application to run successfully.

docker build -t <name to give to your image>

This will start building the image.

Step 3:  We have successfully created a Dockerfile and a respective Docker image for the same.

Step 4: Run the following command in the terminal and it will create a running container with all the needed dependencies and start the application.

docker run -p 9000:80 <image-name>

The 9000 is the port we want to access our application on. 80 is the port the container is exposing for the host to access.

Useful Docker Image commands:

1.)List images

docker ls

Example:

$ docker ls

REPOSITORY          TAG                 IMAGE ID            CREATED             SIZE
nginx               latest              0d9c6c5575f5        4 days ago          126MB
ubuntu              18.04               47b199b0cb85        2 weeks ago         64.2MB

2.)Pull an image from a registry

docker image pull <image-name>

Example:

$ docker pull alpine:3.11

3.11: Pulling from library/alpine
Digest: sha256:9f11a34ef1c67e073069f13b09fb76dc8f1a16f7067eebafc68a5049bb0a072f
Status: Downloaded newer image for alpine:3.11

3.)Remove an Image from Docker

docker rmi <id-of-image>

Example:

$ docker rmi <image_id>

Untagged: <image_id>
Deleted: sha256:<image_id>

4.)Searching for a specific image on Docker Hub

docker search ubuntu

Example:

$ docker search ubuntu

NAME                             DESCRIPTION                                     STARS               OFFICIAL            AUTOMATED
ubuntu                           Ubuntu is a Debian-based Linux operating s...   4458                [OK]               
ubuntu-upstart                   Upstart is an event-based replacement for ...   62                  [OK]               
tutum/ubuntu                     Simple Ubuntu docker images with ssh access     49                  [OK]               
ansible/ubuntu14.04-ansible

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