Feature Flags client

NodeJS client grpc lib, for featureflags service. Provides abilitty to gracefull set and updates for ur features.

Installation

npm i @evo/featureflags-client

Package is uploaded to public npm https://www.npmjs.com/package/@evo/featureflags-client.

Setup

import { FeatureClient, Variable, Types } from '@evo/featureflags-client';

// Default flags dict
const Flags = {
  TEST: false,
  NODE: false
};

const UserIp = new Variable('user.ip', Types.STRING);

const variables = [
    UserIp,
];

const featureClient = new FeatureClient(
  // project name
  'my-cool-project',
  // grpc url
  'grpc:50051',
  // default flags
  Flags,
  // variables are used to conditionally enable flags
  variables,
  // isDebug mode (default: true)
  true,  
  // Optional argument for set interval in milliseconds for fetching flags
  // from service. By default set to 5 min (5 * 60 * 1000).
  1000 * 10,
);

Start

Next start grpc client in async infinite loop, it will be refetching flags values every 5 minutes.

try {
    await featureClient.start();
} catch(e) {
    console.log('[FeatureFlags] client failed to start:', e);
}

Retries

There are 2 options if featureflags client fails to connect to featureflags server:

1. Application will not start.

   This may be desired behavior if application must not work with default flags.

2. Application starts with default flags and retries untill it will connect to featureflags server.

   This behavior is preferable if your application can work with default flags. It will allow you to server requests untill featureflags server will be available again.

   Here is some example of what retry may look like. In this example we are relying on assumption that there is a small outage and server will become available asap. But if server is down for a long time, we will increse retry delay.

   This is just an example and you are free to implement a much simpler or must complex solution.

    /**
     * Use short delay if connection error probably a temporal issue
     */
    const SHORT_RETRY_DELAY = 10000; // 10 sec
    /**
     * Use long delay if connection error probably a long term issue.
     */
    const LONG_RETRY_DELAY = 60000; // 60 sec
    const MAX_SHORT_RETRIES = 5;
   
    /**
     * Try to connect to feature flags server with a small amount of short retries.
     * If short retries failed, keep retrying with long retries with a hope
     * featureflags will be repaired.
     */
    const startWithRetry = (client: FeatureClient) => {
        let retries = 1;
        let delay = SHORT_RETRY_DELAY;
   
        const doRetry = async () => {
            if (retries === MAX_SHORT_RETRIES) {
                logger.error(
                    `[FeatureFlags] reached max amount of short retries: ${MAX_SHORT_RETRIES}. Keep retrying with ${LONG_RETRY_DELAY} ms interval`,
                );
                delay = LONG_RETRY_DELAY;
            }
   
            try {
                await client.start();
                logger.info(`[FeatureFlags] Connected after retry`);
            } catch (e) {
                logger.error(`[FeatureFlags] failed to connect to server - ${retries} attempt, delay ${delay} ms: ${e}`);
                setTimeout(async () => doRetry(), delay);
            } finally {
                retries += 1;
            }
        };
   
        setTimeout(async () => doRetry(), SHORT_RETRY_DELAY);
    };
   
    try {
        await featureClient.start();
    } catch(e) {
        console.log(`[FeatureFlags] failed to connect to server. Start application with default flags and keep retrying: Error - ${e}`,);
        startWithRetry(featureClient);
    }

Usage

Now in you code (controllers, handlers, tasks) call getFlags, and provide there context = {}. Ctx is the object with Variable as a key and a value you want checks to depend on.

import { getFlags } from '@evo/featureflags-client';

// ready to use object with proceeded checks
const flags = getFlags({ 'user.ip': '127.0.0.1' });

if (flags.TEST) doSomeThing();

Proto files

.proto files are vendored. Original protofiles are here

.proto files must be kept in sync with original repo and stubs must be regenerated if needed.

TODO:

• StatsController - Accumulates interval/flag/requests count
• Tracer - Accumulates request/flag/values
• Dummy Manager - For testing purposes