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1-docker.md

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Exercise 1 - Package and Run Application with Docker

Goals

  • Learn how to build and package Docker containers
  • Run the application on Docker
  • Learn about Dockerfile, Kitematic, and port forwarding

Acceptance Criteria

  • Docker image is created and tagged as pet-app
  • Docker container is running and exposing port 8080 (can be seen in Kitematic, if installed)
  • Application can be accessed on http://localhost:8080

Step by Step Instructions

Create a new file called Dockerfile at the root of the project, with the following content:

FROM openjdk:8-jdk-alpine
ARG JAR_FILE

ADD ${JAR_FILE} app.jar
ENTRYPOINT ["java","-Djava.security.egd=file:/dev/./urandom","-jar","/app.jar"]

Ensure the jar file containing the application packaged in step 0 is still available in the target folder. If not, rebuild it and remember the path to the file.

$ ls target/*.jar
target/spring-petclinic-2.0.0.BUILD-SNAPSHOT.jar

Build the container image, passing the path to the jar file as a build argument, as well as the specified tag pet-app:

$ docker build --tag=pet-app --build-arg JAR_FILE=target/spring-petclinic-2.0.0.BUILD-SNAPSHOT.jar .
Sending build context to Docker daemon  49.94MB
Step 1/4 : FROM openjdk:8-jdk-alpine
 ---> 224765a6bdbe
Step 2/4 : ARG JAR_FILE
 ---> Running in 0877d85ce6d9
Removing intermediate container 0877d85ce6d9
 ---> d21d87bb325b
Step 3/4 : ADD ${JAR_FILE} app.jar
 ---> 5847c211645b
Step 4/4 : ENTRYPOINT ["java","-Djava.security.egd=file:/dev/./urandom","-jar","/app.jar"]
 ---> Running in 8222db3a6215
Removing intermediate container 8222db3a6215
 ---> 627600574e8e
Successfully built 627600574e8e
Successfully tagged pet-app:latest

Ensure the container image was created and tagged correctly:

$ docker image ls pet*
REPOSITORY          TAG                 IMAGE ID            CREATED             SIZE
pet-app             latest              627600574e8e        30 seconds ago      140MB

Let's run a docker container in daemon mode to start up our application and expose the container port 8080 in the host:

$ docker run --name=pet-app-prod -d -p 8080:8080 pet-app
11ac55ff100dc341fb47e863f42e01b0579b81c62bc49c8b6f89daf0690c8d48

The long string returned from that command is the container ID. To check its logs:

$ docker logs -f 11ac55ff100dc3

Notice you only require the initial part of the container ID. You can also check the container is running with the docker ps command:

$ docker ps
CONTAINER ID        IMAGE               COMMAND                  CREATED             STATUS              PORTS                    NAMES
11ac55ff100d        pet-app             "java -Djava.securit…"   10 minutes ago      Up 10 minutes       0.0.0.0:8080->8080/tcp   pet-app-prod

If you have Kitematic installed, you can also check the container is running from the UI.

Then you should be able to access the application by going to http://localhost:8080

To shutdown, you can stop and remove the container:

$ docker stop 11ac55ff100dc3
11ac55ff100dc3
$ docker rm 11ac55ff100dc3
11ac55ff100dc3