Who creates the writable Layer?

• Refer here for more info
• Writable layers are created by Storage Drivers
• Storage Drivers:
  • overlay2: Storage driver on all linux flavors
  • aufs : Was a recommended driver for ubuntu earlier
  • devicemapper: Was a recommended driver for centos & RHEL earlier
  • zfs and btrfs: use these drivers when you write a lot

Docker Manual Installation

• Followed instructions from here
• When docker is installed a group called as docker is created. Docker daemon access will be given to this group
• Lets add user to group docker and then exit and reconnect

sudo usermod -aG docker ubuntu

• Execute docker info

Docker CLI

• Refer Here
• One more stuff would use any docker cheatsheet.

Lets Create Docker Image

• This step is also called as containerization of applications
• Scenario 1:
  • Build a container for spring pet clinic
  • Manual Steps
    • Install java8 sudo apt-get update && sudo apt-get install openjdk-8-jdk
    • download spring pet clinic jar file wget https://qt-s3-new-testing.s3-us-west-2.amazonaws.com/spring-petclinic.jar
    • Execute jar file by using following command java -jar spring-petclinic.jar
  • Build a docker image for spring petclinic
    • Two possible base images are
      1. ubuntu
         • Search for ubuntu in DockerHUb
         • Create a directory with a Dockerfile

         FROM ubuntu:18.04
         

         • ADD Metadata to the Dockerfile, we will be using LABEL

         FROM ubuntu:18.04
         LABEL Author="Khaja"
         LABEL Org="QT"
         

         • Lets install java in ubuntu. For that we need to execute the following command ‘apt-get update && apt-get install openjdk-8-jdk -y’

         FROM ubuntu:18.04
         LABEL Author="Khaja"
         LABEL Org="QT"
         RUN apt-get update
         RUN apt-get install openjdk-8-jdk -y
         

         • Writing multiple run statements lead to creation of multiple image layers. so to optimize it lets use &&

         FROM ubuntu:18.04
         LABEL Author="Khaja"
         LABEL Org="QT"
         RUN apt-get update && apt-get install openjdk-8-jdk -y
         ADD https://qt-s3-new-testing.s3-us-west-2.amazonaws.com/spring-petclinic.jar  /spring-petclinic.jar
         

         • Lets build this image

         docker image build -t spc:ubuntu .
         

         • Lets create a container from this image & check the process

         docker container run spc:ubuntu
         docker container ls 
         # container is not shown
         docker ps -a
         

         • As of now the problem is container is getting stopped/killed
         • To recover we need to execute a command during the process of creating container from image. This command should be alive or inwork as long as your container is alive.
         • we observed manually java -jar spring-petclinic.jar exactly does the same thing.
         • To acheive this in docker we add CMD instruction

         FROM ubuntu:18.04
         LABEL Author="Khaja"
         LABEL Org="QT"
         RUN apt-get update && apt-get install openjdk-8-jdk -y
         ADD https://qt-s3-new-testing.s3-us-west-2.amazonaws.com/spring-petclinic.jar  /spring-petclinic.jar
         CMD ["java", "-jar", "/spring-petclinic.jar" ]
         
         

         • building the image & running the container will solve the problem of container being killed. But to access your app you need 8080 port to be accessible. For this we use EXPOSE instruction and in docker container creatiton we use Port Forwarding

         FROM ubuntu:18.04
         LABEL Author="Khaja"
         LABEL Org="QT"
         RUN apt-get update && apt-get install openjdk-8-jdk -y
         ADD https://qt-s3-new-testing.s3-us-west-2.amazonaws.com/spring-petclinic.jar  /spring-petclinic.jar
         EXPOSE 8080
         CMD ["java", "-jar", "/spring-petclinic.jar" ]
         

         • Lets run the container after building the image

         docker image build -t spc:ubuntufinal
         docker container run -p 8088:8080 -d spc:ubuntufinal
         docker container run -P -d spc:ubuntufinal
         # port of host will be decided dynamically
         

      2. If java is installed on the base image
         • By using the openjdk as the base image

         FROM openjdk:8
         LABEL Author="Khaja"
         LABEL Org="QT"
         ADD https://qt-s3-new-testing.s3-us-west-2.amazonaws.com/spring-petclinic.jar  /spring-petclinic.jar
         EXPOSE 8080
         CMD ["java", "-jar", "/spring-petclinic.jar" ]
         

         • Now run the container after building the image and check it.
      3. using alpine jdk to optimize image size

      FROM openjdk:8u212-jdk-alpine3.9
      LABEL Author="Khaja"
      LABEL Org="QT"
      ADD https://qt-s3-new-testing.s3-us-west-2.amazonaws.com/spring-petclinic.jar  /spring-petclinic.jar
      EXPOSE 8080
      CMD ["java", "-jar", "/spring-petclinic.jar" ]
      

        Compare sizes of the docker image by executing docker images