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Java HTTP Server

This is a simple HTTP server written in the Java programming language.

To run this example, follow these steps:

1. Install the CLI and a container runtime engine, for example Docker. Use the unikraft CLI or the legacy kraft CLI.

2. Clone the examples repository and cd into the examples/httpserver-java21 directory:

Code
git clone https://github.com/unikraft-cloud/examples
cd examples/httpserver-java21/

Make sure to log into Unikraft Cloud and pick a metro close to you. This guide uses fra (Frankfurt, 🇩🇪):

When done, invoke the following command to deploy this app on Unikraft Cloud:

The output shows the instance address and other details:

Code
[●] Deployed successfully!
 │
 ├────────── name: httpserver-java21-5xw9m
 ├────────── uuid: b2c3d4e5-f6a7-8901-bcde-f12345678901
 ├───────── state: starting
 ├──────── domain: https://gentle-wind-b2x9pkqm.fra.unikraft.app
 ├───────── image: httpserver-java21@sha256:4f8a2c6e1d9b3f7a5c0e2b4d8f6a1c3e7b9d2f4a6c8e0b2d4f6a8c0e2b4d6f
 ├──────── memory: 1 GiB
 ├─────── service: gentle-wind-b2x9pkqm
 ├── private fqdn: httpserver-java21-5xw9m.internal
 ├──── private ip: 172.16.3.5
 └────────── args: /usr/lib/jvm/java-21-openjdk-amd64/bin/java -classpath /usr/src/ SimpleHttpServer

In this case, the instance name is httpserver-java21-5xw9m and the address is https://gentle-wind-b2x9pkqm.fra.unikraft.app. They're different for each run.

Use curl to query the Unikraft Cloud instance of the Java HTTP server:

Code
curl https://gentle-wind-b2x9pkqm.fra.unikraft.app

Code
Hello, World!

You can list information about the instance by running:

Code
NAME                      FQDN                              STATE    STATUS       IMAGE                                 MEMORY  VCPUS  ARGS                                                 BOOT TIME
httpserver-java21-5xw9m   gentle-wind-b2x9pkqm.fra.unik...  running  since 3mins  httpserver-java21@sha256:4f8a2c6e...  1 GiB   1      /usr/lib/jvm/java-21-openjdk-amd64/bin/java -cla...  421.30 ms

When done, you can remove the instance:

Customize your app

To customize the app, update the files in the repository, listed below:

• Kraftfile: the Unikraft Cloud specification
• Dockerfile: the Docker-specified app filesystem
• SimpleHttpServer.java: the Java HTTP server implementation

Lines in the Kraftfile have the following roles:

• spec: v0.6: The current Kraftfile specification version is 0.6.

• runtime: base-compat:latest: The kernel to use.

• rootfs: ./Dockerfile: Build the app root filesystem using the Dockerfile.

• cmd: ["/usr/lib/jvm/java-21-openjdk-amd64/bin/java", "-classpath", "/usr/src/", "SimpleHttpServer"]: Use the Java runtime to run SimpleHttpServer as the starting command of the instance.

Lines in the Dockerfile have the following roles:

• FROM --platform=linux/x86_64 ubuntu:24.04 AS build: Build the app using Ubuntu 24.04, which includes Java 21 in its official repositories.

• RUN apt-get ... install openjdk-21-jdk ...: Install OpenJDK 21.

• RUN javac SimpleHttpServer.java: Compile the Java source file.

• FROM scratch: Build the runtime filesystem from a minimal base image.

• COPY ...: Copy required files to the app filesystem: system libraries, the Java 21 runtime, and the compiled SimpleHttpServer.class.

The following options are available for customizing the app:

• If you only update the implementation in the SimpleHttpServer.java source file, you don't need to make any other changes.

• If you want to add extra files, you need to copy them into the filesystem using the COPY command in the Dockerfile.

• If you want to replace SimpleHttpServer.java with a different source file, update the cmd line in the Kraftfile and replace SimpleHttpServer with the name of your new class.

• More extensive changes may require extending the Dockerfile (see Dockerfile syntax reference).

Learn more

• Java's Documentation
• Unikraft Cloud's Documentation
• Building Dockerfile images with Buildkit

Use the --help option for detailed information on using Unikraft Cloud:

Or visit the CLI Reference or the legacy CLI Reference.