17

Java

This directory contains the Java runtime on Unikraft, in binary compatibility mode. It implements a simple HTTP server running on Unikraft that provides a simple response to each request.

Run and Use

Use kraft to run the image and start a Unikraft instance:

kraft run --rm -M 1024M -p 8080:8080 --plat qemu --arch x86_64 unikraft.org/java:17

If the --plat argument is left out, it defaults to qemu. If the --arch argument is left out, it defaults to your system's CPU architecture.

Once executed, it will open port 8080 and wait for connections. To test it, you can use curl:

curl localhost:8080

You should see a "Hello, World!" message.

Inspect and Close

To list information about the Unikraft instance, use:

kraft ps -a

NAME          KERNEL                      ARGS                               CREATED        STATUS   MEM    PORTS                   PLAT
upbeat_jenny  project://java:qemu/x86_64  /usr/lib/jvm/java-17-openjdk[...]  5 seconds ago  running  1020M  0.0.0.0:8080->8080/tcp  qemu/x86_64

The instance name is upbeat_jenny. To close the Unikraft instance, use:

kraft rm upbeat_jenny

Note that closing the kraft run command (e.g., via Ctrl+c) does not kill the Unikraft instance. If you want the Unikraft instance closed when closing the kraft run command, use the --rm option:

kraft run --rm -M 1024M -p 8080:8080 --plat qemu --arch x86_64 unikraft.org/java:17

Build and Run Locally

The commands so far used the pre-build Java image available in the Unikraft registry.

In oder to to build a local Java image, clone this repository and cd into this directory. Then use kraft to build an image locally:

kraft build --no-cache --no-update --plat qemu --arch x86_64

Similar to the kraft run command, if the --plat argument is left out, it defaults to qemu. If the --arch argument is left out, it defaults to your system's CPU architecture.

In order to run the locally built image, use . (dot, the current directory) as the final argument to the kraft run command:

kraft run --rm -M 1024M -p 8080:8080 --plat qemu --arch x86_64 .

Same as above, it will open port 8080 and wait for connections.

kraft and sudo

Mixing invocations of kraft and sudo can lead to unexpected behavior. Read more about how to start kraft without sudo at https://unikraft.org/sudoless.

Learn More

• How to run unikernels locally
• How to build Dockerfile root filesystems with BuildKit