๐Ÿ”˜ Unleash

Unleash is a robust feature flagging solution that you can roll out to your team easily today. It's easy to use, comes with a lot of features and support for both server-side and client-side languages and frameworks.

Unleash: The Largest Open-Source Feature Flag Management
Feature flags should be simple and powerful. Private cloud or self-hosted. Multi-region. Safe and transparent.

Great software teams feature flag. Unleash (code) provides a F/OSS off-the-shelf solution to feature flagging that you can bring to your team today. Here's how it's architected:

Unleash architecture

The diagram is a little busy, but the server-side usage is a bit clearer:

// Unleash server side usage (NodeJS)

const { initialize } = require('unleash-client');

const unleash = initialize({
  url: 'https://YOUR-API-URL',
  appName: 'my-node-name',
  customHeaders: { Authorization: 'SOME-SECRET' },

// Usage of a specific toggle
const demoToggle = unleash.isEnabled('DemoToggle');

And in various clients (web apps, mobile apps, etc):

// Unleash client side usage (iOS w/ Swift)

import SwiftUI
import UnleashProxyClientSwift

// Setup Unleash in the context where it makes most sense

var unleash = UnleashProxyClientSwift.UnleashClient(unleashUrl: "https://<unleash-instance>/api/frontend", clientKey: "<client-side-api-token>", refreshInterval: 15, appName: "test")


While in the past teams may have used environment variables or home-grown configuration sources (Database, files, APIs) to see whether a feature toggle is available, Unleash provides a solution that is easy to roll out and easy to manage (that your team doesn't have to maintain!).

Unleash can be controlled and driven via API (it also has a OpenAPI/Swagger spec!), so it can be integrated into many workflows quite easily, here's a curl example:

curl -H "Content-Type: application/json" \
     -H "Authorization: MY-ADMIN-API-KEY" \
     -X POST \
     -d '{
  "name": "my-unique-feature-name",
  "description": "lorem ipsum..",
  "type": "release",
  "enabled": false,
  "stale": false,
  "strategies": [
      "name": "default",
      "parameters": {}
  "variants": [],
  "tags": []
}' \

Unleash has extensive documentation and very clear guides on how it's built and how to do various kinds of testing, like A/B testing.

Running Unleash

Unleash is quite docker friendly, with support for both running docker-compose and docker to start the individual pieces.

You can use the Unleash docker-compose.yml, which looks like this:

version: "3.9"

  # The Unleash server contains the Unleash configuration and
  # communicates with server-side SDKs and the Unleash Proxy
    image: unleashorg/unleash-server:latest
      - "4242:4242"
      # This points Unleash to its backing database (defined in the `db` section below)
      DATABASE_URL: "postgres://postgres:unleash@db/postgres"
      # Disable SSL for database connections. @chriswk: why do we do this?
      DATABASE_SSL: "false"
      # Changing log levels:
      LOG_LEVEL: "warn"
      # Proxy clients must use one of these keys to connect to the
      # Proxy. To add more keys, separate them with a comma (`key1,key2`).
      INIT_FRONTEND_API_TOKENS: "default:development.unleash-insecure-frontend-api-token"
      # Initialize Unleash with a default set of client API tokens. To
      # initialize Unleash with multiple tokens, separate them with a
      # comma (`token1,token2`).
      INIT_CLIENT_API_TOKENS: "default:development.unleash-insecure-api-token"
        condition: service_healthy
    command: [ "node", "index.js" ]
      test: wget --no-verbose --tries=1 --spider http://localhost:4242/health || exit 1
      interval: 1s
      timeout: 1m
      retries: 5
      start_period: 15s
      - "5432"
    image: postgres:15
      # create a database called `db`
      POSTGRES_DB: "db"
      # trust incoming connections blindly (DON'T DO THIS IN PRODUCTION!)
      interval: 2s
      timeout: 1m
      retries: 5
      start_period: 10s

Check out the documentation on how to get started for more information.

For greater control, you can also start the official container image manually:

docker run \
  -p 4242:4242 \
  -e DATABASE_HOST=postgres \
  -e DATABASE_NAME=unleash \
  -e DATABASE_USERNAME=unleash_user \
  -e DATABASE_PASSWORD=some_password \
  -e DATABASE_SSL=false \
  --name unleash \
  --pull=always unleashorg/unleash-server

The official docker image has instructions and is well-maintained as well.

Note that the above docker run command assumes that you have a Postgres database ย running, so you might want to start that first (and read up on how to use/maintain the database!):

docker run \
  -e POSTGRES_USER=unleash_user \
  -e POSTGRES_PASSWORD=some_password \
  -e POSTGRES_DB=unleash \
  --name postgres \