DevOps Classroomnotes 11/Jun/2022

Install Docker on a linux machine

• Create a linux vm
  • AWS EC2 Refer Here
  • Azure VM Refer Here
• Softwares to be installed on your system
  • Refer Here
  • Windows Terminal Refer Here
• Installing latest version of docker on linux

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

* After installing docker, the connection between client and docker engine is not working due to permission issue

* Option 1: run docker as root user

* Option 2: Add current user to the docker group

sudo usermod -aG docker <username>
# exit and relogin

Image Building process

• overview:
  

Manual approach

• To build a image that runs our application, we need to know the manual steps of running our application.
• In this case, lets consider the application to be spring pet clinic.
  • runtime: Java 11 (JDK 11)
  • software package Refer Here
  • runs on port 8080
• To build a image we will be using existing image, When we pick the existing image for our application
  • option 1: take a image and install runtime and download package
  • option 2: take a image which already has a runtime & download and run application.
• We have opted for option 2 and chosen openjdk:11 (image:tag).
• Lets create a container and login into it

docker container run -p <port of linux>:<port of application> -it <image>:<tag> <terminal>
docker container run -p 8080:8080 -it openjdk:11 /bin/bash

* Now exit after downloading the application

* Now in this container we have spring petclinic
* Now lets create image from container

Automated Approach

• We need to create Dockerfile.
• The Dockerfile has set of instructions

<INSTRUCTION> VALUE

• Sample Dockerfile

FROM openjdk:11
LABEL author=khaja
RUN wget https://referenceapplicationskhaja.s3.us-west-2.amazonaws.com/spring-petclinic-2.4.2.jar
EXPOSE 8080
CMD ["java", "-jar", "/spring-petclinic-2.4.2.jar"]

• In the above Dockerfile the instructions are
  • FROM
  • LABEL
  • RUN
  • EXPOSE
  • CMD
• This Dockerfile when executed with docker image build -t <image>:<tag> <directory with docker file> will try to create a container based on base image and run all the necessary instructions and creates the image
• When we start the container from image whatever is mentioned in CMD/ENTRYPOINT gets executed.
• Lets try to create one more application gameoflife. This application requires
  • server: tomcat
  • runtime: java 8
  • port 8080
  • Download gameoflife into webapps https://referenceapplicationskhaja.s3.us-west-2.amazonaws.com/gameoflife.war
• Refer Here for the tomcat image

FROM tomcat:9.0.64-jdk8-temurin-focal
LABEL author=khaja
LABEL why=forfun
RUN curl https://referenceapplicationskhaja.s3.us-west-2.amazonaws.com/gameoflife.war --output /usr/local/tomcat/webapps/gameoflife.war
EXPOSE 8080

• Lets build to create image
  
• Refer Here for Dockerfile Instructions