DevOps Classroomnotes 11/Jun/2022

Install Docker on a linux machine

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

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* After installing docker, the connection between client and docker engine is not working due to permission issue
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* Option 1: run docker as root user
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* Option 2: Add current user to the docker group

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

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Image Building process

  • overview:
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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

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* Now exit after downloading the application
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* Now in this container we have spring petclinic
* Now lets create image from container
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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
  • 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
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  • Refer Here for Dockerfile Instructions

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