Unleash React - Configuring Unleash Proxy

This post is part of a series on adding feature flagging to a React application using Unleash.

Unleash React - What is Feature Flagging?
Feature flags are a powerful tool in the developer’s toolbox. Instead of releasing code in large features and risky deployment operations, new features can be developing incrementally and turned on and off in production by toggling a flag, selecting certain users, or other similar strategies. This m…

In this post, we're going to talk about using Unleash from our React application.


To use Unleash in server-side code, all you need is the server running and one of the Unleash SDKs. However, lightweight frontend applications, like React or mobile apps, need to take a different approach to remain highly performant. This is why Unleash has developed the Unleash Proxy. It essentially acts as a client SDK to the Unleash server, allowing lightweight apps to proxy requests through it.

Unleash Proxy is also available as a docker image. Just like when we configured the Unleash Server, we will be using docker-compose to run the proxy.


We will be creating another docker-compose.yml file for the Unleash Proxy. You may ask yourself why we don't just add it to the previous one and start them all together. Good question!

Unfortunately, there is no way to specify an API key for the Unleash Server when starting it, so it can't be known ahead of time to provide when starting the Unleash Proxy. This means we need to start the server, configure the API key, then start the proxy using that key.

So, let's go ahead and get that API key ready.


First, login to the server that you started previously. You will see a menu icon in the top left corner. Open the menu and go to Admin


Navigate to API ACCESS and click the button to ADD NEW API KEY.


Give the API key a name and select Client for the API type.


Once you have created the key, you will see it listed. Copy the Secret value, which is the API token.


Now we will start the Unleash Proxy in docker. First, since we will be using two separate docker-compose files, we need to create a shared virtual network they can use to communicate.

docker network create unleash-net

Now update the docker-compose.yml file for the Unleash Server to include the network and re-run docker-compose up.

version: "3.4"
services:
  db:
    image: postgres:10-alpine
    environment:
      POSTGRES_DB: "db"
      POSTGRES_HOST_AUTH_METHOD: "trust"
    expose:
      - 5432
  unleash:
    image: unleashorg/unleash-server
    ports:
      - "4242:4242"
    environment:
      DATABASE_URL: "postgres://postgres:[email protected]/postgres"
      DATABASE_SSL: "false"
    depends_on:
      - db

networks:
  default:
    external:
      name: unleash-net

Next, in a new folder, save the yaml below into a file called docker-compose.yml. Replace [paste_api_token] with the copied secret value from Unleash. Replace some-secret with any secret of your choice, to later be used to authenticate to the proxy from the React app.

version: "3.4"
services:
  unleash-proxy:
    image: unleashorg/unleash-proxy
    ports:
      - "3000:3000"
    environment:
      UNLEASH_URL: "http://unleash:4242/api"
      UNLEASH_API_TOKEN: "[paste_api_token]"
      UNLEASH_PROXY_SECRETS: "some-secret"

networks:
  default:
    external:
      name: unleash-net

Now run docker-compose up. This will start the Unleash Proxy to communicate on the virtual network with the Unleash Server via its service name unleash from the other docker-compose.yml file.


Once Unleash Proxy is running, you can test it out using curl.

curl http://[docker_host_ip_address]:3000/proxy -H "Authorization: some-secret"

You should see a json response containing all defined toggles.

{"toggles":[]}%

Let's go ahead and create a feature toggle in Unleash to make sure we see it here.

Navigate to the Unleash Server web UI and click the CREATE FEATURE TOGGLE button. Create the feature like below. We will use it next in the React app. The default Standard strategy will be created.


Try the curl command again and see the new feature toggle included in the json response.

curl http://[docker_host_ip_address]:3000/proxy -H "Authorization: some-secret"
{"toggles":[{"name":"weather","enabled":true,"variant":{"name":"disabled","enabled":false}}]}%

Now that the Unleash Proxy is running and we have a feature toggle created, we can start using it from a React app.