Initial Feature Flag Fetch Returns Default Value Instead of Rollout Value

[barath121]

I’m observing an issue where fetching feature flags initially sends back the default value rather than the intended rollout value. This can affect real-time logic that depends on precise feature values at the start of the session.

Sharing code where i was able to reproduce this issue:

const {
    EdgeFeatureHubConfig,
    Readyness, 
    FHLog,
    StrategyAttributeCountryName
} = require('featurehub-javascript-node-sdk');

const express = require('express');
const app = express();
const PORT = process.env.PORT || 3000;

FHLog.fhLog.trace = (...args) => console.log(args);

async function init() {
    const fhConfig = new EdgeFeatureHubConfig(process.env.FEATUREHUB_EDGE_URL, process.env.FEATUREHUB_CLIENT_API_KEY);
    fhConfig.addReadinessListener((readyness, firstTimeReady) => {
        if (firstTimeReady) {
            console.log("Connected to feature hub");
        }
        if (readyness === Readyness.NotReady) {
            console.log("Connection is not ready");
        }
        if (readyness === Readyness.Failed) {
            console.log("Unable to connect to feature hub");
        }
    });

    fhConfig.init();
    let fhClient = fhConfig.newContext();

    app.get('/healthz', (req, res) => {
        console.log(fhConfig.readyness);
        if (fhConfig.readyness === Readyness.Ready) {
            res.status(200).json({ done: 'ok' });
        } else {
            res.status(500).json({ done: 'not ready' });
        }
    });
    
    app.get("/", async (req, res) => {
        await fhClient.country(StrategyAttributeCountryName.Iceland).build();

        console.log(
            fhConfig.readyness,
            fhClient.feature('booleanFlag').getBoolean(),
            fhClient.feature('StringFlag').getString()
        );

        if (fhClient.feature('booleanFlag').getBoolean()) {
            res.status(200).json({ "hello": "hello" });
        } else {
            res.status(401).json({ "hello": "hello" });
        }
    });

    app.listen(PORT, () => {
        console.log(`Server running on http://localhost:${PORT}`);
    });
}

init();

[rvowles]

So if you have a string value set with a default of "blue" and strategy of "yellow" (for country Iceland) and once the app is healthy and has state, your app prints "blue"? We also need to know which version of featurehub plz :-)

[barath121]

Yes i use /healthz to check if the feature hub is ready. Then when i hit / i get blue instead of yellow first time then it switched to yellow on further tries.
Node library version - 1.3.3
Feature hub version - 1.8.1.

[barath121]

@rvowles Did you get a chance to check this out?

[rvowles]

Hi there, @IrinaSouth is taking a look at this

[IrinaSouth]

Hi @barath121

I tried to replicate but all appears to work for me. I have used your code exactly, just added some prints:

        console.log(
            "Readiness is " + fhConfig.readyness,
            "Boolean flag is " + fhClient.feature('booleanFlag').getBoolean(),
            "String flag is " + fhClient.feature('StringFlag').getString()
        );

And when I loaded http://localhost:3000/ it gave me the following on first time:
Readiness is Ready Boolean flag is false String flag is yellow

And the strategy that I have set in featurehub on the "StringFlag" feature looks like this:

You will also see some log from the sdk like this that might confused you, which will show default value and strategies array, so the strategy value won't be displayed:

[
  'received features',
  [
    {
      id: 'a77be8e4-f372-416b-b2a3-dbdec87b9f4b',
      key: 'StringFlag',
      l: false,
      version: 1,
      type: 'STRING',
      value: 'green',
      strategies: [Array]
    },
    {
      id: '85b201a6-32da-439f-b1ed-1d493fb2fe29',
      key: 'booleanFlag',
      l: true,
      version: 1,
      type: 'BOOLEAN',
      value: false
    }
  ]

[IrinaSouth]

@barath121

Updated code:

const {
    EdgeFeatureHubConfig,
    Readyness,
    FHLog,
    StrategyAttributeCountryName
} = require('featurehub-javascript-node-sdk');

const express = require('express');
const app = express();
const PORT = process.env.PORT || 3000;

FHLog.fhLog.trace = (...args) => console.log(args);

async function init() {
    const fhConfig = new EdgeFeatureHubConfig(process.env.FEATUREHUB_EDGE_URL, process.env.FEATUREHUB_CLIENT_API_KEY);
    fhConfig.addReadinessListener((readyness, firstTimeReady) => {
        if (firstTimeReady) {
            console.log("Connected to feature hub");
        }
        if (readyness === Readyness.NotReady) {
            console.log("Connection is not ready");
        }
        if (readyness === Readyness.Failed) {
            console.log("Unable to connect to feature hub");
        }
    });

    fhConfig.init();
    let fhClient = fhConfig.newContext();

    app.get('/healthz', (req, res) => {
        console.log(fhConfig.readyness);
        if (fhConfig.readyness === Readyness.Ready) {
            res.status(200).json({ done: 'ok' });
        } else {
            res.status(500).json({ done: 'not ready' });
        }
    });

    app.get("/", async (req, res) => {
        await fhClient.country(StrategyAttributeCountryName.Iceland).build();

        console.log(
            "Readiness is " + fhConfig.readyness,
            "Boolean flag is " + fhClient.feature('booleanFlag').getBoolean(),
            "String flag is " + fhClient.feature('StringFlag').getString()
        );

        if (fhClient.feature('booleanFlag').getBoolean()) {
            res.status(200).json({ "hello": "hello" });
        } else {
            res.status(401).json({ "hello": "hello" });
        }
    });

    app.listen(PORT, () => {
        console.log(`Server running on http://localhost:${PORT}`);
    });
}

init();

[barath121]

Thankyou @IrinaSouth.

[barath121]

@IrinaSouth I am trying to use the code again but still facing similar issue.
I have a boolean flag named enable_key4 which is true if platform_version header is v2.0.0 and false in other cases.
Whenever the header value changes the client becomes unready and sends default value can you share what can be done here.
I have tried the same for python client it works perfectly there, attaching both codes here.
Node.js:

const {
    EdgeFeatureHubConfig,
    FeatureHubPollingClient,
    Readyness,
    FHLog,
    featurehubMiddleware    
} = require('featurehub-javascript-node-sdk');

const express = require('express');
const app = express();
const PORT = process.env.PORT || 3000;

FHLog.fhLog.trace = (...args) => console.log(args);

async function init() {
    const fhConfig = new EdgeFeatureHubConfig(process.env.FEATUREHUB_EDGE_URL, process.env.FEATUREHUB_CLIENT_API_KEY);
    
    let fhClient = fhConfig.newContext();
    // fhConfig.addReadinessListener((ready, firstTime) => {

    // }, true);
    
    fhConfig.init();
    
    app.use(async (req,res,next)=>{
        req.featureContext = await fhClient.attributeValue('platform_version', req.headers.platform_version).build();        
        next();
    })

    app.get('/healthz', (req, res) => {
        console.log(fhConfig.readyness);
        if (fhConfig.readyness === Readyness.Ready) {
            res.status(200).json({ done: 'ok' });
        } else {
            res.status(500).json({ done: 'not ready' });
        }
    });

    app.get("/", async (req, res) => {
        if (fhConfig.readyness !== Readyness.Ready) {
            console.log('Feature flags not ready yet');
            return res.status(503).json({ error: 'Feature flags not ready yet' });
        }
        let featureFlag;
        const responseObject = {
            key1: 1,
            key2: 2,
            key3: 3
        }
        featureFlag = req.featureContext.feature('enable_key4').getBoolean();
        
        if(featureFlag){
            responseObject["key4"] = 4;
        }
        
        res.status(200).json(responseObject);
    });

    app.listen(PORT, () => {
        console.log(`Server running on http://localhost:${PORT}`);
    });
}

init();

Python:

from fastapi import FastAPI, Request, HTTPException
from featurehub_sdk.featurehub_config import FeatureHubConfig
import os
import uvicorn

app = FastAPI()

FEATUREHUB_EDGE_URL = os.getenv("FEATUREHUB_EDGE_URL")
FEATUREHUB_CLIENT_API_KEY = os.getenv("FEATUREHUB_CLIENT_API_KEY")

fh_config = FeatureHubConfig(FEATUREHUB_EDGE_URL, [FEATUREHUB_CLIENT_API_KEY])
fh_config.use_polling_edge_service()

@app.on_event("startup")
async def startup_event():
    await fh_config.init()

@app.middleware("http")
async def feature_context_middleware(request: Request, call_next):
    platform_version = request.headers.get("platform_version")
    print(platform_version)

    context = await fh_config.new_context().attribute_values("platform_version", platform_version).build()
    request.state.feature_context = context
    response = await call_next(request)
    return response

@app.get("/healthz")
async def healthz():
    print(fh_config.repository().is_ready())
    if fh_config.repository().is_ready():
        return {"done": "ok"}
    else:
        raise HTTPException(status_code=500, detail="not ready")

@app.get("/")
async def root(request: Request):
    response_object = {
        "key1": 1,
        "key2": 2,
        "key3": 3
    }

    feature_flag = request.state.feature_context.feature("enable_key4").get_flag
    print(feature_flag)
    if feature_flag:
        response_object["key4"] = 4

    return response_object

if __name__ == "__main__":
    uvicorn.run(app, host="0.0.0.0", port=int(os.getenv("PORT", 3000)))

[rvowles]

Heya - your node code isn't right unfortunately. You cannot have a single context for the entire application, you need to have a context per request, you are mixing browser style coding (where there is a single context) with node style (which is where there is one per request).

For node you need to be making sure you are using a client evaluated key, and in your middleware, you need to ask for a new context - so app.use(() => req.featureContext = fhClient.newContext().attributeValue......build());

If you don't do that, you are changing the global config and it will replace the repository and go back to being blank.

[barath121]

@IrinaSouth Thanks this works