# Express HTTP Server

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

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[Express](https://expressjs.com/) is a fast, unopinionated, minimalist web framework for Node.js.

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-expressjs4.18-node21` directory:

```bash
git clone https://github.com/unikraft-cloud/examples
cd examples/httpserver-expressjs4.18-node21/
```

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-expressjs418-node21:latest
unikraft run --scale-to-zero policy=on,cooldown-time=1000 --metro fra -p 443:3000/tls+http -m 512M --image <my-org>/httpserver-expressjs418-node21:latest
```

```bash title="kraft"
kraft cloud deploy --scale-to-zero on --scale-to-zero-cooldown 1s -p 443:3000/tls+http -M 512Mi .
```

</CodeTabs>

The output shows the instance address and other details:

<CodeTabs syncKey="cli">

```ansi title="unikraft"
metro:        fra
name:         httpserver-expressjs418-node21-lb3p2
uuid:         a1b2c3d4-e5f6-7890-abcd-ef1234567890
state:        starting
image:        <my-org>/httpserver-expressjs418-node21
resources:
  memory:     512MiB
  vcpus:      1
service:
  uuid:       aa081882-8173-7ea1-4136-aeee1d7d2316
  name:       calm-ocean-r9x4mk7v
  domains:
  - fqdn:     calm-ocean-r9x4mk7v.fra.unikraft.app
networks:
- uuid:       98ee012f-7acb-82f2-ddcb-7866393890a6
  private-ip: 10.0.3.4
  mac:        12:b0:97:42:f6:d9
timestamps:
  created:    just now
```

```ansi title="kraft"
[●] Deployed successfully!
 │
 ├───────── name: httpserver-expressjs418-node21-lb3p2
 ├───────── uuid: a1b2c3d4-e5f6-7890-abcd-ef1234567890
 ├──────── metro: https://api.fra.unikraft.cloud/v1
 ├──────── state: starting
 ├─────── domain: https://calm-ocean-r9x4mk7v.fra.unikraft.app
 ├──────── image: oci://unikraft.io/<my-org>/httpserver-expressjs418-node21@sha256:2e7d3f1a9c4b8e05d6f2a3b7c1e4d8f0a2b5c9e3d7f1a4b8
 ├─────── memory: 512 MiB
 ├────── service: calm-ocean-r9x4mk7v
 ├─ private fqdn: httpserver-expressjs418-node21-lb3p2.internal
 └─── private ip: 10.0.3.4
```

</CodeTabs>

In this case, the instance name is `httpserver-expressjs418-node21-lb3p2` and the address is `https://calm-ocean-r9x4mk7v.fra.unikraft.app`.
They're different for each run.

Use `curl` to query the Unikraft Cloud instance of the Express.js-based HTTP web server:

```bash
curl https://calm-ocean-r9x4mk7v.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-expressjs418-node21-lb3p2  running  <my-org>/httpserver-expressjs418-node21        512MiB  1      calm-ocean-r9x4mk7v.fra...  2 minutes ago
```

```ansi title="kraft"
NAME                                  FQDN                        STATE    STATUS       IMAGE                                                                 MEMORY   VCPUS  ARGS  BOOT TIME
httpserver-expressjs418-node21-lb3p2  calm-ocean-r9x4mk7v.fra...  running  since 3mins  oci://unikraft.io/<my-org>/httpserver-expressjs418-node21@sha256:...  512 MiB  1            312.45 ms
```

</CodeTabs>

When done, you can remove the instance:

<CodeTabs syncKey="cli">

```bash title="unikraft"
unikraft instances delete httpserver-expressjs418-node21-lb3p2
```

```bash title="kraft"
kraft cloud instance remove httpserver-expressjs418-node21-lb3p2
```

</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
* `app/index.js`: the Express.js 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/bin/node", "/usr/src/server.js"]`: Use `/usr/bin/node /usr/src/server.js` as the starting command of the instance.

Lines in the `Dockerfile` have the following roles:

* `FROM node:21-alpine AS build`: Build the app using the Node.js 21 Alpine image.

* `COPY ...`: Copy required files to the app filesystem: the `node` binary executable, libraries, configuration files, and the Express.js app.

* `RUN npm install`: Install Express.js and other dependencies.

The following options are available for customizing the app:

* If you only update the implementation in the `app/index.js` 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 `app/index.js` with a different source file, update the `cmd` line in the `Kraftfile` and replace `/usr/src/server.js` with the path to your new source file.

* More extensive changes may require extending the `Dockerfile` ([see `Dockerfile` syntax reference](https://docs.docker.com/engine/reference/builder/)).

## Learn more

- [Express's Documentation](https://expressjs.com/en/5x/api.html)
- [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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