DevOps Classroom Series – 11/Jun/2020

Docker commands

  • Recomendation is to use docker command line reference over here or a cheatsheet over here
  • other option to read manual by using –help

Docker Registry

  • Docker Hub is Default Registry Refer Here
  • There are many private docker registries
    • AWS Elastic Container Registry (ECR)
    • Azure Container Registry (ACR)
    • Aritifactory
    • Docker registry (Docker Image) Refer Here
    • and many more

Docker Images and how to create them

  • Docker image is a packaging format to run an application on docker engine as a container
  • What docker image has?
    • includes everything to run an application
      • code or binaries
      • runtime
      • dependencies
      • other filesystem objects
  • From one docker image we can create multiple containers
  • How can a Docker image be created?
    • Converting existing container into docker image
    • Export VMs to Docker Image
    • Create DockerImage using Dockerfile (Recommended approach)

Docker image building steps

  1. To build a docker image we should always take some existing docker image as a base
  2. Get the steps to configure your application on this docker image
  3. Now try to use Dockerfile Instructions to create Docker image

Lets try to understand how to build image for a java app (Spring pet clinic)

  • Lets write the manual steps.
    1. Install java 8
    2. Download spring petclinic jar file from here
    3. Run the application
  • Commands
# Install Java
sudo apt-get update && sudo apt-get install openjdk-8-jdk -y

# Download jar

# Run the application
java -jar spring-petclinic-2.2.0.BUILD-SNAPSHOT.jar
  • This application can be viewed on port 8080

Using Above Steps lets create Dockerfile

  1. Create some folder (hellodocker)
  2. Now create a file Dockerfile in this folder
  3. Find a base image
    • Now lets experiment with docker base image ubuntu.
    • Lets create a container with ubuntu image docker container run -it ubuntu /bin/bash
    • Now execute the following commands
    apt-get update
    apt-get install openjdk-8-jdk wget -y
    # Now to start application
    java -jar spring-petclinic-2.2.0.BUILD-SNAPSHOT.jar
    • Since we need to install java and the rest why dont we take a base image with java already installed? so lets use openjdk:8 image
    • Lets create a contianer with openjdk image docker container run -it openjdk:8 /bin/bash
    • Now execute the following commands
    # Now to start application
    java -jar spring-petclinic-2.2.0.BUILD-SNAPSHOT.jar
  4. Dockerfile for approach using ubuntu as base image
FROM ubuntu  
RUN apt-get update && apt-get install openjdk-8-jdk wget -y
RUN wget
CMD java -jar spring-petclinic-2.2.0.BUILD-SNAPSHOT.jar
  1. Now build the docker image using docker image build command
cd ~/hellodocker
docker image build -t hellodocker .
docker image ls

Preview Preview 6. Lets run the container using the image

docker container run -d -P hellodocker
  1. Exercise: Use this docker file to create a image called as hellodocker2 Dockerfile for approach using openjdk as base image
FROM openjdk:8
RUN wget
CMD ["java",  "-jar",  "spring-petclinic-2.2.0.BUILD-SNAPSHOT.jar"]

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