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Example apps

Express HTTP Server

Express is a fast, unopinionated, minimalist web framework for Node.js.

To run this example, follow these steps:

1. Install the unikraft CLI. You need a BuildKit builder. The easiest way to get one is via Docker. Alternatively, you can also directly set up and use BuildKit, see the quick start.

2. Clone the examples repository and cd into the examples/httpserver-expressjs4.18-node21 directory:

   Code
   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 close to you. This guide uses fra (Frankfurt, 🇩🇪):

Code
unikraft login

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

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

The output shows the instance address and other details:

Code
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

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:

Code
curl https://calm-ocean-r9x4mk7v.fra.unikraft.app

Code
Hello, World!

You can list information about the instance by running:

Code
unikraft instances list

Code
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

When done, you can remove the instance:

Code
unikraft instances delete httpserver-expressjs418-node21-lb3p2

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.

• 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).

Learn more

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

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

Code
unikraft --help

Or visit the CLI Reference.