How to set up local unleash client for feature flag?

Question

I'm trying to setup a feature flag for a Typescript project. The code below is from the https://www.npmjs.com/package/unleash-client. Where I create and connect to an unleash instance. This is all with a locally running unleash setup as per this documentation: https://github.com/Unleash/unleash. It seems from the error, I'm not able to connect to unleash. I have verified the instance is running locally in the docker container as per the docs. I can also see the service up and running in my browser. Would anyone know why I'm getting the error below when I try to connect?

CODE:

import express from 'express';
import { Unleash } from 'unleash-client';

const unleash = new Unleash({
  url: 'http://localhost:4242/api/',
  appName: 'default',
  customHeaders: { Authorization: 'default:development.unleash-insecure-api-token' },
});

ERROR LOG:

FetchError: Unleash Repository error: request to http://localhost:4242/api/client/features failed, reason: connect ECONNREFUSED 127.0.0.1:4242
app-local-backend                  | [1]     at ClientRequest.<anonymous> (/app/node_modules/minipass-fetch/lib/index.js:130:14)
app-local-backend                  | [1]     at ClientRequest.emit (node:events:517:28)
app-local-backend                  | [1]     at Socket.socketErrorListener (node:_http_client:501:9)
app-local-backend                  | [1]     at Socket.emit (node:events:517:28)
app-local-backend                  | [1]     at emitErrorNT (node:internal/streams/destroy:151:8)
app-local-backend                  | [1]     at emitErrorCloseNT (node:internal/streams/destroy:116:3)
app-local-backend                  | [1]     at process.processTicksAndRejections (node:internal/process/task_queues:82:21) {
app-local-backend                  | [1]   code: 'ECONNREFUSED',
app-local-backend                  | [1]   errno: 'ECONNREFUSED',
app-local-backend                  | [1]   syscall: 'connect',
app-local-backend                  | [1]   address: '127.0.0.1',
app-local-backend                  | [1]   port: 4242,
app-local-backend                  | [1]   type: 'system'
app-local-backend                  | [1] }

What is weirder is that I can access the endpoint as per the documentation in postman as may be seen below:

Any assistance with this would be much appreciated!

Nuno Góis · Accepted Answer · 2024-02-06 17:04:14Z

I tried reproducing the issue but was unable to. Your code looks correct to me.

Is it possible you're running your application in isolation, e.g. in a separate Docker container, so it is unable to reach localhost:4242 on your host machine?

If you can reach Unleash at localhost:4242 through your browser and Postman, then I would suggest you start by trying to create a new local project just to see if that works. Something like:

import { initialize } from 'unleash-client'

const TOGGLE = 'unleash-node-test'

const unleash = initialize({
  url: 'http://localhost:4242/api',
  appName: 'unleash-node-test',
  customHeaders: {
    Authorization:
      'default:development.unleash-insecure-api-token'
  }
})

const checkToggles = () => {
  const enabled = unleash.isEnabled(TOGGLE)
  const variant = unleash.getVariant(TOGGLE)
  console.log(TOGGLE)
  console.log('isEnabled', enabled)
  console.log('getVariant', variant)
  setInterval(checkToggles, 5000)
}

unleash.on('ready', checkToggles)

If it works, then I would look into any specificities of the environment you're running your other application in and try to address them.

KCH · Accepted Answer · 2024-08-28 14:18:54Z

1

This may be due to ipv6 shenanigans. First attempt at connection will be ipv6 which will fail and ipv4 isn't attempted. Try adding this somewhere before you attempt connection.

dns.setDefaultResultOrder('ipv4first');

answered Aug 28, 2024 at 14:18

KCH

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