# Java HTTP Server

import { Tabs, TabsContent, TabsList, TabsTrigger } from "zudoku/ui/Tabs"

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This is a simple HTTP server written in the [Java](https://www.java.com/en/) programming language.

To run this example, follow these steps:

1. Install the CLI.
   Use the [unikraft CLI](/cli/unikraft) or the legacy [kraft CLI](https://unikraft.org/docs/cli/install).
   You need a [BuildKit](https://github.com/moby/buildkit) builder. The easiest way to get one is via [Docker](https://docs.docker.com/engine/install/).
   Alternatively, you can also directly set up and use BuildKit, see the [quick start](https://github.com/moby/buildkit#quick-start).

:::note
The unikraft CLI is the current standard, while kraft is the legacy version.
Choose one of the CLIs below and only run the commands associated with it for the rest of this guide.
:::

2. Clone the [`examples` repository](https://github.com/unikraft-cloud/examples) and `cd` into the `examples/httpserver-java21` directory:

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

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

<CodeTabs syncKey="cli">

```bash title="unikraft"
unikraft login
```

```bash title="kraft"
# Set Unikraft Cloud access token
export UKC_TOKEN=token
# Set metro to Frankfurt, DE
export UKC_METRO=fra
```

</CodeTabs>

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

<CodeTabs syncKey="cli">

```bash title="unikraft"
unikraft build . --output <my-org>/httpserver-java21:latest
unikraft run --scale-to-zero policy=idle,cooldown-time=1000,stateful=true --metro fra -p 443:8080/tls+http -m 1G --image <my-org>/httpserver-java21:latest
```

```bash title="kraft"
kraft cloud deploy --scale-to-zero idle --scale-to-zero-stateful --scale-to-zero-cooldown 1s -p 443:8080/tls+http -M 1Gi .
```

</CodeTabs>

The output shows the instance address and other details:

<CodeTabs syncKey="cli">

```ansi title="unikraft"
metro:        fra
name:         httpserver-java21-5xw9m
uuid:         b2c3d4e5-f6a7-8901-bcde-f12345678901
state:        starting
image:        <my-org>/httpserver-java21
resources:
  memory:     1GiB
  vcpus:      1
service:
  uuid:       9d96e042-1601-352b-10c7-4a8c7ececbcb
  name:       gentle-wind-b2x9pkqm
  domains:
  - fqdn:     gentle-wind-b2x9pkqm.fra.unikraft.app
networks:
- uuid:       25185154-a4d5-0da1-e28f-3b3e42190b56
  private-ip: 10.0.3.5
  mac:        12:b0:29:0f:68:f3
timestamps:
  created:    just now
```

```ansi title="kraft"
[●] Deployed successfully!
 │
 ├───────── name: httpserver-java21-5xw9m
 ├───────── uuid: b2c3d4e5-f6a7-8901-bcde-f12345678901
 ├──────── metro: https://api.fra.unikraft.cloud/v1
 ├──────── state: starting
 ├─────── domain: https://gentle-wind-b2x9pkqm.fra.unikraft.app
 ├──────── image: oci://unikraft.io/<my-org>/httpserver-java21@sha256:4f8a2c6e1d9b3f7a5c0e2b4d8f6a1c3e7b9d2f4a6c8e0b2d4f6a8c0e2b4d6f
 ├─────── memory: 1 GiB
 ├────── service: gentle-wind-b2x9pkqm
 ├─ private fqdn: httpserver-java21-5xw9m.internal
 └─── private ip: 10.0.3.5
```

</CodeTabs>

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:

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

```text
Hello, World!
```

You can list information about the instance by running:

<CodeTabs syncKey="cli">

```bash title="unikraft"
unikraft instances list
```

```bash title="kraft"
kraft cloud instance list
```

</CodeTabs>

<CodeTabs syncKey="cli">

```ansi title="unikraft"
METRO  NAME                     STATE    IMAGE                       ARGS  MEMORY  VCPUS  FQDN                              CREATED
fra    httpserver-java21-5xw9m  running  <my-org>/httpserver-java21        1GiB    1      gentle-wind-b2x9pkqm.fra.unik...  2 minutes ago
```

```ansi title="kraft"
NAME                     FQDN                              STATE    STATUS       IMAGE                                                    MEMORY  VCPUS  ARGS  BOOT TIME
httpserver-java21-5xw9m  gentle-wind-b2x9pkqm.fra.unik...  running  since 3mins  oci://unikraft.io/<my-org>/httpserver-java21@sha256:...  1 GiB   1            421.30 ms
```

</CodeTabs>

When done, you can remove the instance:

<CodeTabs syncKey="cli">

```bash title="unikraft"
unikraft instances delete httpserver-java21-5xw9m
```

```bash title="kraft"
kraft cloud instance remove httpserver-java21-5xw9m
```

</CodeTabs>

## 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: v0.7`: The current `Kraftfile` specification version is `0.7`.

* `runtime: base-compat:latest`: The kernel to use.

* `rootfs`: Build the app root filesystem.
  `source: ./Dockerfile` means the filesystem is built using the `Dockerfile`.
  `format: erofs` means the filesystem type is [EROFS](https://erofs.docs.kernel.org/).

* `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](https://docs.docker.com/engine/reference/builder/)).

## Learn more

- [Java's Documentation](https://docs.oracle.com/en/java/)
- [Unikraft Cloud's Documentation](https://unikraft.cloud/docs/)
- [Building `Dockerfile` images with `Buildkit`](https://unikraft.org/guides/building-dockerfile-images-with-buildkit)


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

<CodeTabs syncKey="cli">

```bash title="unikraft"
unikraft --help
```

```bash title="kraft"
kraft cloud --help
```

</CodeTabs>

Or visit the [CLI Reference](/cli/unikraft) or the [legacy CLI Reference](/cli/kraft/overview).
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