flagbearer for Ruby

The Ruby SDK for Flagbearer. Requires Ruby 3.2 or later.

Install

bundle add flagbearer

Keys

Use a server key, which starts with fbs_. Server keys are secret: read them from the environment, such as FLAGBEARER_SERVER_KEY, and never put them in browser code or in the repository. Browsers use client keys, which start with fbc_, through @flagbearer/web.

Sync at startup

Create one client per process, when the app starts, and wait for it to sync before accepting requests. In Rails, use an initializer:

# config/initializers/flagbearer.rb
FLAGS = Flagbearer.init(ENV.fetch("FLAGBEARER_SERVER_KEY"))

begin
  FLAGS.sync(timeout: 10)
rescue Flagbearer::Error => e
  # Keep starting: checks use their defaults, and the SDK retries in the background.
  Rails.logger.warn("Initial Flagbearer sync failed: #{e.message}")
end

at_exit { FLAGS.close }

Check per request

Pass each request's user explicitly, and a default:

class SearchController < ApplicationController
  def index
    user = { key: current_user.id.to_s, email: current_user.email }
    @advanced = FLAGS.enabled?("advanced-search", user, default: false)
  end
end

The user is a Hash with :key and :email, as symbol or string keys. The key must be a String, so convert numeric IDs with to_s.

The email is optional. Include it to turn flags on for testers by email. The default is used until the client has synced, and when the flag doesn't exist.

Shut down

Keep the client for the life of the process, not per request. Close it on shutdown, as the initializer above does with at_exit.

Short-lived jobs, like a Rake task or a serverless function, should call FLAGS.flush before they exit.