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Example apps

Node WebSocket Server

WebSocket is a bidirectional communication protocol over TCP, compatible with HTTP. This example builds an echo-reply WebSocket server in Node.

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/node21-websocket/ directory:

   Code
   git clone https://github.com/unikraft-cloud/examples
   cd examples/node21-websocket/

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>/node21-websocket:latest
unikraft run --metro fra \
  -m 1G \
  -p 443:8080/tls+http \
  --scale-to-zero policy=on,cooldown-time=1000,stateful=true \
  --image <my-org>/node21-websocket:latest

The output shows the instance address and other details:

Code
metro:        fra
name:         node21-websocket-j2x9r
uuid:         d5e6f7a8-b9c0-1d2e-3f4a-d5e6f7a8b9c0
state:        starting
image:        <my-org>/node21-websocket
resources:
  memory:     1024MiB
  vcpus:      1
service:
  uuid:       e6f7a8b9-c0d1-2e3f-4a5b-e6f7a8b9c0d1
  name:       lively-breeze-hp3wx6yt
  domains:
  - fqdn:     lively-breeze-hp3wx6yt.fra.unikraft.app
networks:
- uuid:       f7a8b9c0-d1e2-3f4a-5b6c-f7a8b9c0d1e2
  private-ip: 10.0.5.4
  mac:        12:b0:d3:af:12:0c
timestamps:
  created:    just now

In this case, the instance name is node21-websocket-j2x9r and the address is https://lively-breeze-hp3wx6yt.fra.unikraft.app. They're different for each run.

The command will build the files in the current directory.

After deploying, you can query the service with a WebSocket client, such as wscat. Install wscat with npm:

Code
npm install -g wscat

Then query the WebSocket server deployed on Unikraft Cloud, using its URL:

Code
wscat --connect wss://<NAME>.<METRO>.unikraft.app

Then enter messages, that will be replied by the server.

You can list information about the instance by running:

Code
unikraft instances list

Code
METRO  NAME                    STATE    IMAGE                      ARGS  MEMORY   VCPUS  FQDN                                     CREATED
fra    node21-websocket-j2x9r  running  <my-org>/node21-websocket        1024MiB  1      lively-breeze-hp3wx6yt.fra.unikraft.app  2 minutes ago

When done, you can remove the instance:

Code
unikraft instances delete <instance-name>

Learn more

• WebSocket documentation
• ws: A Node.js WebSocket library
• 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.