Containerizing, packaging, and running a Spring Boot application

Note	This repository contains the guide documentation source. To view the guide in published form, view it on the Open Liberty website.

Learn how to containerize, package, and run a Spring Boot application on Open Liberty without modification.

What you’ll learn

The starting point of this guide is the finished application from the Building an Application with Spring Boot guide. If you are not familiar with Spring Boot, complete that guide first. Java 21 is required to run this project.

You will learn how to use the springBootUtility command to deploy a Spring Boot application in Docker on Open Liberty without modification. This command stores the dependent library JAR files of the application to the target library cache, and packages the remaining application artifacts into a thin application JAR file. Optionally, you will learn how to use Liberty InstantOn with your Spring Boot application for faster startup.

You will also learn how to run the Spring Boot application locally with Open Liberty, and how to package it so that it is embedded with an Open Liberty server package.

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Building and running the application

First, build the initial Spring Boot application into an executable JAR file. Navigate to the start directory and run the Maven package command:

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cd start
mvnw.cmd package

cd start
./mvnw package

cd start
./mvnw package

You can now run the application in the embedded Tomcat web container by executing the JAR file that you built:

java -jar target/guide-spring-boot-0.1.0.jar

After you see the following messages, the application is ready:

... INFO ... [ main] com.example.springboot.Application : Started Application in 2.511 seconds (process running for 3.24)
Let's inspect the beans provided by Spring Boot:
application
...
welcomePageHandlerMapping
welcomePageNotAcceptableHandlerMapping

Go to the http://localhost:8080/hello URL to access the application.

The following output is displayed in your browser:

Greetings from Spring Boot!

When you need to stop the application, press CTRL+C in the command-line session where you ran the application.

Building and running the application in a Docker container

You will build an Open Liberty Docker image to run the Spring Boot application. Using Docker, you can run your thinned application with a few simple commands. For more information on using Open Liberty with Docker, see the Containerizing microservices guide.

Learn more about Docker on the official Docker website.

Install Docker by following the instructions in the official Docker documentation.

Navigate to the start directory.

Create the Dockerfile in the start directory.
Dockerfile

Dockerfile

link:finish/Dockerfile[role=include]

This Dockerfile is written in two main stages. For more information about multi-stage Dockerfiles, see the documentation on the official Docker website.

The first stage copies the guide-spring-boot-0.1.0.jar Spring Boot application to the /staging temporary directory, and then uses the Open Liberty springBootUtility command to thin the application. For more information about the springBootUtility command, see the springBootUtility documentation.

The second stage begins with the Open Liberty Docker image. The Dockerfile copies the Liberty server.xml configuration file from the /opt/ol/wlp/templates directory, which enables Spring Boot and TLS support. Then, the Dockerfile copies the Spring Boot dependent library JAR files that are at the lib.index.cache directory and the thin-guide-spring-boot-0.1.0.jar file. The lib.index.cache directory and the thin-guide-spring-boot-0.1.0.jar file were both generated in the first stage.

Use the following command to build the Docker image:

docker build -t springboot .

To verify that the images are built, run the docker images command to list all local Docker images:

docker images

Your springboot image appears in the list of Docker images:

REPOSITORY    TAG       IMAGE ID         CREATED           SIZE
springboot    latest    3a5492c0cbeb     27 seconds ago    485MB

Now, you can run the Spring Boot application in a Docker container:

docker run -d --name springBootContainer --rm -p 9080:9080 -p 9443:9443 springboot

Before you access your application from the browser, run the docker ps command to make sure that your container is running:

docker ps

You see an entry similar to the following example:

CONTAINER ID        IMAGE               COMMAND                  CREATED             STATUS              PORTS                                            NAMES
e33532aa07d6        springboot          "/opt/ol/helpers/run…"   7 seconds ago       Up 2 seconds        0.0.0.0:9080->9080/tcp, 0.0.0.0:9443->9443/tcp   springBootContainer

You can watch the application start by monitoring the logs:

docker logs springBootContainer

Wait several seconds for the following message, which indicates that Liberty’s startup is complete:

...
CWWKZ0001I: Application thin-guide-spring-boot-0.1.0 started in 8.033 seconds.
...
CWWKF0011I: The defaultServer server is ready to run a smarter planet.
The defaultServer server started in 11.065 seconds.

Note that the thin-guide-spring-boot-0.1.0 application took 8.033 seconds to start.

After the application starts, go to the http://localhost:9080/hello URL to access the application.

After you are finished checking out the application, stop your container by running the following command:

docker stop springBootContainer

Optional: Faster container startup with InstantOn

Liberty InstantOn provides fast startup times for MicroProfile and Jakarta EE applications. In this section, you’ll learn how to build an InstantOn image that provides fast startup times. Your application can start in milliseconds, without compromising on throughput, memory, development-production parity, or Java language features.

Liberty InstantOn requires a Linux system with kernel version 5.9 or greater. You can run the following command to check the kernel version of your system:

uname -r

If your kernel version is older than 5.9, you can skip this section and move on to the Running the application on Open Liberty section.

The Coordinated Restore at Checkpoint (crac) Liberty feature enables applications to use the Liberty InstantOn implementation of the org.crac APIs. When the org.crac APIs are enabled, checkpoint and restore can work with applications written using the Spring Framework.

Replace the Dockerfile in the start directory.
Dockerfile

Dockerfile

link:instantOn/Dockerfile[role=include]

crac.xml

link:finish/src/main/liberty/instantOn/crac.xml[role=include]

The COPY command copies the provided crac.xml configuration file to the Liberty configDropins configuration directory. The crac.xml file enables the crac feature to the Liberty instance.

Run the following command to rebuild the Docker image:

docker build -t springboot .

To take a checkpoint of the application process with the afterAppStart option, run the following command:

docker run \
  --name springBootCheckpointContainer \
  --privileged \
  --env WLP_CHECKPOINT=afterAppStart \
  springboot

When the application process checkpoint completes, the springBootCheckpointContainer application container is stopped and exits. The stopped springBootCheckpointContainer container contains the data from the InstantOn checkpoint process. Take this checkpoint process data and commit it to an application container image layer called springboot-instanton, run the following commands:

docker commit springBootCheckpointContainer springboot-instanton
docker rm springBootCheckpointContainer

The stopped springBootCheckpointContainer container is no longer needed and can safely be removed.

To verify that the InstantOn image is built, run the docker images command to list all local Docker images:

docker images

Your springboot-instanton image appears in the list of Docker images.

REPOSITORY             TAG      IMAGE ID       CREATED          SIZE
springboot-instanton   latest   c4aabcdd64bf   20 seconds ago   583MB
springboot             latest   3a5492c0cbeb   14 minutes ago   484MB

Run the springboot-instanton InstantOn application image by running the following command:

docker run \
  --rm -d \
  --name springBootContainer \
  --cap-add=CHECKPOINT_RESTORE \
  --cap-add=SETPCAP \
  --security-opt seccomp=unconfined \
  -p 9080:9080 \
  springboot-instanton

Run the following command to see the container logs:

docker logs springBootContainer

You see more logs from Spring for restoring. Liberty’s startup is complete in less than a second. It shows a faster startup time of 0.874 seconds than the original springboot image that you built in the previous section.

2024-11-22T16:33:43.349Z  INFO 1027 --- [ecutor-thread-1] o.s.c.support.DefaultLifecycleProcessor  : Restarting Spring-managed lifecycle beans after JVM restore
...
2024-11-22T16:33:43.562Z  INFO 1027 --- [ecutor-thread-1] w.s.c.ServletWebServerApplicationContext : Root WebApplicationContext: initialization completed in 135784 ms
2024-11-22T16:33:43.568Z  INFO 1027 --- [ecutor-thread-1] o.s.c.support.DefaultLifecycleProcessor  : Spring-managed lifecycle restart completed (restored JVM running for 525 ms)
...
CWWKZ0001I: Application thin-guide-spring-boot-0.1.0 started in 0.874 seconds.
...
CWWKF0011I: The defaultServer server is ready to run a smarter planet.
The defaultServer server started in 0.897 seconds.

Go to the http://localhost:9080/hello URL to access the application.

After you are finished checking out the application, stop your container by running the following command:

docker stop springBootContainer

If you use Podman instead of Docker, you can build your InstantOn image in a simplified way. Read the Building the InstantOn image with Podman and the checkpoint.sh script documentation.

To learn more about the Liberty InstantOn feature, see the Faster startup for containerized applications with Open Liberty InstantOn documentation.

Running the application on Open Liberty

Next, you will run the Spring Boot application locally on Open Liberty by updating the pom.xml file.

The pom.xml was created for you in this directory.

Update the Maven POM file in the start directory.
pom.xml

pom.xml

link:finish/pom.xml[role=include]

Add the liberty-maven-plugin to the pom.xml file.

The liberty-maven-plugin downloads and installs Open Liberty to the target/liberty directory. The installAppPackages configuration element in the pom.xml file typically takes in the following parameters: dependencies, project, or all. The default value is dependencies, but to install the Spring Boot application to Open Liberty, the value must be spring-boot-project. This value allows Maven to package, thin, and copy the guide-spring-boot-0.1.0.jar application to the Open Liberty runtime applications directory and shared library directory.

To run the Spring Boot application, the Open Liberty instance needs to be correctly configured. By default, the liberty-maven-plugin picks up the Liberty server.xml configuration file from the src/main/liberty/config directory.

Create the Liberty server.xml configuration file.
src/main/liberty/config/server.xml

server.xml

link:finish/src/main/liberty/config/server.xml[role=include]

The servlet and springBoot features are required for the Liberty instance to run the Spring Boot application. The application port is specified as 9080 and the application is configured as a springBootApplication element. For more information, see the springBootApplication element documentation.

If you didn’t build the Spring Boot application, run the package goal:

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mvnw.cmd package

./mvnw package

./mvnw package

Next, run the liberty:run goal. This goal creates the Open Liberty instance, installs required features, deploys the Spring Boot application to the Open Liberty instance, and starts the application.

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mvnw.cmd liberty:run

./mvnw liberty:run

./mvnw liberty:run

After you see the following message, your Liberty instance is ready:

The defaultServer server is ready to run a smarter planet.

Go to the http://localhost:9080/hello URL to access the application.

After you finish exploring the application, press CTRL+C to stop the Open Liberty instance. Alternatively, you can run the liberty:stop goal from the start directory in a separate command-line session:

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mvnw.cmd liberty:stop

./mvnw liberty:stop

./mvnw liberty:stop

Packaging the application embedded with Open Liberty

You can update the pom.xml file to bind more Open Liberty Maven goals to the package phase. Binding these goals to the package phase allows the Maven package goal to build a Spring Boot application that is embedded with Open Liberty.

Update the Maven POM file in the start directory.
pom.xml

pom.xml

link:finish/pom.xml[role=include]

Add the include and packageName configuration elements, and the executions element to the pom.xml file.

The include configuration element specifies the minify, runnable values. The runnable value allows the application to be generated as a runnable JAR file. The minify value packages only what you need from your configuration files without bundling the entire Open Liberty install.

The packageName configuration element specifies that the application is generated as a GSSpringBootApp.jar file.

The executions element specifies the required Open Liberty Maven goals to generate the application that is embedded with Open Liberty.

Next, run the Maven package goal:

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mvnw.cmd package

./mvnw package

./mvnw package

Run the repackaged Spring Boot application. This JAR file was defined previously in the pom.xml file.

java -jar target/GSSpringBootApp.jar

After you see the following message, your Liberty instance is ready:

The defaultServer server is ready to run a smarter planet.

Go to the http://localhost:9080/hello URL to access the application.

When you need to stop the application, press CTRL+C.

Great work! You’re done!

You just ran a basic Spring Boot application with Open Liberty.

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