fastify-feature-flags

Fastify feature flags plugin. By default it has built-in provider for config module. However it could be extended by various plugins that implement simple interface.

This plugin is currently in beta, so some bugs can appear. Feel free to create an issue and I'll try to fix them asap.

ToC

• fastify-feature-flags
  • ToC
  • Fastify support
  • Installation
  • Features and requirements
  • Usage
    • Providers
      • Generic provider
      • Config provider
      • Env provider
      • Unleash provider
    • Using plugin
  • Docs
  • Changelog
  • See also
  • License

Fastify support

• v1.x.x - supports >= fastify-1.0.0, including v2.x.x versions.

Installation

npm i fastify-feature-flags --save

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Features and requirements

• Requires fastify >=1.0.0.
• Node.js >=8.9.0.

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Usage

Add it to your project like regular fastify plugin. Use register method and pass options to it.

const fastify = require('fastify');
const app = fastify();

const ffPlugin = require('fastify-feature-flags');
const ConfigProvider = require('fastify-feature-flags/dist/providers/config');
app.register(ffPlugin, {providers: [new ConfigProvider()]});

Plugin adds an object with built-in providers and generic provider interface that you can extend. For checking features availability it adds two methods: fastify.featureFlags.isEnabled which returns true or false and fastify.featureFlags.checkEnabled which throws an error if feature is disabled. The list of built-in providers is available below.

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Providers

Generic provider

Generic provider is an abstract class that you may extend to add new providers. It should have isEnabled method that consumes feature name and context (optionally) and returns true or false.

Config provider

Reads feature flags from specified config section. Depends on config module. You should install it manually. It's constuctor consumes options object that contains prefix for config section where features are defined.

Example:

default.js (in config directory):

module.exports = {
  features: {
    a: true,
    b: false,
  }
}

Configuring provider:

const ConfigProvider = require('fastify-feature-flags/dist/providers/config');
const provider = new ConfigProvider({
  prefix: 'features',
})

Valid config values for feature to be enabled are: true, "true" or "1". Last two may be useful if you're using config module with env overrides.

Env provider

Reads feature flags from env variables. It's constuctor consumes options object that may contain prefix for filtering env variables containing features.

Example:

default.js (in config directory):

FEATURE_A = true
FEATURE_B = false

Configuring provider:

const EnvProvider = require('fastify-feature-flags/dist/providers/env');
const provider = new EnvProvider({
  prefix: 'FEATURE_',
})

Valid config values for feature to be enabled are: "true" or "1".

Unleash provider

This provider relies on feature flags service Unleash. You should install the module manually.

Example:

Configuring provider:

const UnleashProvider = require('fastify-feature-flags/dist/providers/unleash');
const provider = new UnleashProvider({
  appName: 'my-fastify-app',
  url: 'https://unleash.example.com/api',
})

For more options please refer to unleash docs

Using plugin

After configuring providers and registering the plugin in your fastify app you can use isEnabled or checkEnabled methods.

You may also specify multiple providers, then the feature will be enabled only when it will be enabled in all providers.

Example:

const fastify = require('fastify')();
const ffPlugin = require('fastify-feature-flags');
const EnvProvider = require('fastify-feature-flags/dist/providers/env');

fastify.register(ffPlugin, {
  providers: [new EnvProvider({prefix: 'FEATURE_'})]
});

fastify.get('/a', async (request, reply) => {
  await fastify.featureFlags.checkEnabled('A');
  reply.type('application/json').code(200);
  return { a: 'enabled' };
});

fastify.get('/b', async (request, reply) => {
  const isEnabled = await fastify.featureFlags.isEnabled('B');
  reply.type('application/json').code(200);
  return { b: isEnabled };
});

(async () => {
  await fastify.ready();
  await fastify.listen(3000);
})();

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Docs

See docs.

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Changelog

See changelog.

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See also

• unleash - feature toogle service.

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License

Licensed under MIT.

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