FROM openjdk:17-alpine: This line specifies the base image for the Docker image. In this case, it's using the Alpine Linux-based OpenJDK 17 image.

ARG JAR_FILE=target/UserRegistrationService-1.1-SNAPSHOT.jar: This line declares an argument named JAR_FILE and sets its default value to target/UserRegistrationService-1.1-SNAPSHOT.jar. This argument will be used later in the Dockerfile. When we run the below command: docker build -t danvi/user-registration-service:1.1 --build-arg JAR_FILE=target/UserRegistrationService-1.1-SNAPSHOT.jar . // it can be 1.0, 1.1, 1.2 etc...

In the above command, the --build-arg option allows you to specify the value for the JAR_FILE build argument. By changing the value of the JAR_FILE argument during the build process, you can build Docker images with different versions of the JAR file without modifying the Dockerfile itself.

ADD ${JAR_FILE} userregistration.jar: This line copies the JAR file specified by the JAR_FILE argument from the build context into the Docker image and renames it to userregistration.jar.

ENTRYPOINT ["java","-jar","/userregistration.jar"]: This line sets the default command to run when the container starts. It runs the Java application inside the container using the java -jar command and specifies the userregistration.jar file as the application JAR.

way 1: Using Host machine IP(our system IP) if 2 or more docker containers want to communicate.

way 2 Create a docker compose file and define the services to make them connected to same network then containers can communicate with each other using container/service names.

1st docker image: When we run springboot application image docker image, it becomes a container and it has its own HOST IP and localhost specific to this container itself(lets say this is user-registration-service container).

2nd docker image: When we run mysql image which was pulled from docker cloud officially, it becomes a container and it has its own HOST IP and localhost specific to this container itself(lets say this is mysql container).