DevOps Classroom Series – 19/Mar/2021

Dockerfile

• Docker can build images by reading instructions from a Dockerfile
• Lets take one more application as an example
  • This application is based on java
  • This application runs on port 8080
• Lets try to install this java application on a linux machine first
• create a ubuntu linux vm on any cloud. login into linux machine using ssh
  • install java
  • download spring pet clinic application

sudo apt update
sudo apt install openjdk-8-jdk -y
java -version
wget https://referenceappkhaja.s3-us-west-2.amazonaws.com/spring-petclinic-2.2.0.BUILD-SNAPSHOT.jar
java -jar spring-petclinic-2.2.0.BUILD-SNAPSHOT.jar

• Now navigate to http://publicip:8080
• To create a docker
  • We have to choose a right base image
    • You can choose ubuntu and perform all the steps
    • Choose a image where java is already installed
• To build Dockerfile we will be using instructions Refer Here
• So lets build a Dockerfile using ubuntu:18.04 image
  • To set the base image we will be using FROM instrution Refer Here
  • Now we need to divide our commands which we use to install/configure our application into two sections
    • application installation/configuration steps. All the configuration steps we will be using can be written in Dockerfile with RUN instruction Refer Here

    apt update
    apt install openjdk-8-jdk wget -y
    wget https://referenceappkhaja.s3-us-west-2.amazonaws.com/spring-petclinic-2.2.0.BUILD-SNAPSHOT.jar
    

    • application execution steps. Execution steps will be configured with instruction CMD Refer Here

    java -jar spring-petclinic-2.2.0.BUILD-SNAPSHOT.jar
    

    • Our application when executed might require some port to connect, in this case the port is 8080, we use EXPOSE instruction to specify ports of application Refer Here
• Create a folder and then place the Dockerfile in it. Now build the docker image using docker image build command Refer Here

docker image build -t spc:ubuntu .

• Now lets check the docker images in the local machine (local repository) docker image ls Refer Here
• Building a Image using openjdk image
• To copy the jar file into container use the ADD instruction Refer Here
• Lets try to build the docker image

docker image build -t spc:openjdk .

• Lets view the docker image in the local registry
• Now lets try to run the application in a docker container using two images which we have built
• To build a docker image for an app we will have multiple approaches, try to use the approach which is simpler and which results in consuming less resources
• Refer Here for the dockerfiles used in the class room
• Refer Here for the slim version of spc