Containerizing Applications (Building Docker Images)
- To build the Docker Images, we will be using the Dockerfile approach
- Refer Here for the official docs of Dockerfile
- In Dockerfile we use instructions mentioned in the above reference.
<INSTRUCTION> <VALUE>
- The basic instructions are
- FROM => Helps in choosing the base image
- RUN => Adds the execution/installation on the base image to build our application
- LABEL => ADDS metadata
- ENV => Set ENVIRONMENT variables
- EXPOSE => PORTS to be exposed by application
- ADD/COPY => Content to be added into the image from local or from urlss
- USER => User with which container has to be started (if not specificed root)
- WORKDIR => Working Directory
- ARG => Build time arguments
- CMD => Command that will be called when container is created
- ENTRYPOINT => Command that will be called when container is created
- Activity 3: Lets create a image for an Spring boot based application (Java Spring boot):
- Manually running the application:
- Ensure java is installed (Java 8 or Java 11)
- Download the jar file of your application
- Find the port on which your application runs
- EXECUTE the following command to start application
java -jar <app.jar>
- For the Spring Petclinic Sample app Refer Here
- This application runs on java 11. The port it exposes is 8080
- Manual Steps:
bash
sudo apt update
sudo apt install openjdk-11-jdk -y
wget https://referenceapplicationskhaja.s3.us-west-2.amazonaws.com/spring-petclinic-2.4.2.jar
java -jar spring-petclinic-2.4.2.jar - Now to choose a base image we would prefer a base image with JAVA 11 installed.
- Refer Here for the Dockerfile created.
- Now create a image using Docker image build
- Now lets look at images
- Now lets try to create the container using spc:1.0
docker container run -d --name myspc1 -P spc:1.0 - Lets see if we can this better, we can use the slim version of the open jdk which gives the exact same result i.e. our application will be working from a docker image of much less size. Refer Here
