DevOps Classroom notes 28/Jan/2025

Installing docker on Ubuntu Linux

• Lets create an ec2 instance / azure vm
• ssh into it
• execute the following commands to get the latest version of docker

curl -fsSL https://get.docker.com -o install-docker.sh
sudo sh install-docker.sh

• After this installation, a group called as docker is created. all the users who are part of this group can use docker
• Lets add a current user to docker group

sudo usermod -aG docker <username>

• Exit and relogin
• now execute docker info
  

Containerize the application

• This means ensuring application developed (by your org) is running inside container.
• This also means we need to create a image (docker image) of our application

Images

• docker images will have following naming pattern <name>:<tag>
• <name> represents the image name of your application and <tag> represents the version
• if the <tag> is not passed the default value is latest
• In Docker hub we have 3 types of images
  • Docker official images:
    • Generally these images have <name>:<tag>
    • Examples
      • nginx
      • alpine
      • openjdk
  • verified publisher images
    • Generally these images have <publisher>/<name>:<tag>
    • Examples:
      • jenkins/jenkins
  • individual images
    • Generally these images have <username>/<name>:<tag>
    • Examples:
      • shaikkhajaibrahim/skate

How to build images

• To build a docker image first know the manual steps involved in bringing up your application.
• Once we have steps, then we have two approaches in building images
  • manual approach which involved creating a container & taking a snapshot (commit)
  • automatable & repetitive approach referred as Dockerfile approach.

Lets build a docker image to have openjdk 17

• Findout the steps involved in installing openjdk 17 on
  • ubuntu:
    bash
sudo apt update
sudo apt install openjdk-17-jdk -y
  • alpine
    apk update
apk add --no-cache openjdk17 gcompat

Manual approach with ubuntu

• pull ubuntu image

docker image pull ubuntu:24.04

• Now create a container in an interactive mode

docker container run -it --name ubuntujava ubuntu:24.04 /bin/bash

• Now run the commands

apt update
apt install openjdk-17-jdk -y

• verify if java is installed

java -version

• Now exit from container and execute commit command to create image

docker container commit ubuntujava jdk17:ubuntu

• Lets create a container using new image and cross check if java is present or not

docker container run -it jdk17:ubuntu /bin/bash
java -version

• Exercise: Try the same for alpine jdk17:alpine