flipper-firebase_remote_config

A Flipper adapter that stores feature state in Firebase Remote Config. Useful when you want flags reachable from both your Ruby backend and your Firebase-using mobile / web clients without standing up a separate flag store.

Firebase Remote Config is eventually consistent and rate-limited for writes (Firebase publishes a daily write quota per project, on the order of hundreds of writes/day). This makes it a poor fit for:

• Per-request flag flipping
• High-frequency A/B test ramping
• Anything that depends on a write being visible immediately

It is a good fit for low-frequency operational toggles that you want a single source of truth for across server and client platforms.

Always wrap this adapter with Flipper::Adapters::Memoizable or the per-request Flipper::Middleware::Memoizer to avoid a Remote Config fetch on every flag check.

# Gemfile
gem 'flipper-firebase_remote_config'

require 'flipper'
require 'flipper/adapters/firebase_remote_config'
require 'flipper/adapters/memoizable'

Flipper.configure do |config|
  config.adapter do
    base = Flipper::Adapters::FirebaseRemoteConfig.new(
      project_id:  ENV.fetch('FIREBASE_PROJECT_ID'),
      credentials: ENV.fetch('GOOGLE_APPLICATION_CREDENTIALS'), # path to service-account JSON
      prefix:      'flipper__',  # optional, default 'flipper__'
      cache_ttl:   30,           # optional, default 30 seconds
    )
    Flipper::Adapters::Memoizable.new(base)
  end
end

The service account needs the Firebase Remote Config Admin role (or equivalent custom role granting cloudconfig.configs.get and cloudconfig.configs.update).

credentials accepts:

• A file path to a service-account JSON key (String)
• An open IO/StringIO containing service-account JSON
• A pre-built Google::Auth::* credentials object
• nil to fall back to Application Default Credentials

Each Flipper feature becomes one Remote Config parameter, named <prefix><feature_key>. The parameter's defaultValue.value is a JSON blob representing the gate state:

{
  "boolean": "true",
  "actors": ["1", "2"],
  "groups": ["admins"],
  "percentage_of_actors": "25",
  "percentage_of_time": null
}

A sentinel parameter <prefix>__index__ holds a JSON array of all known feature keys, so listing features doesn't have to scan every parameter.

Remote Config uses ETag-based optimistic concurrency. The adapter:

1. Fetches the template + ETag (cached for cache_ttl seconds).
2. Mutates the template in memory.
3. Publishes with If-Match: <etag>.
4. On a 412 Precondition Failed, reloads and retries once. If the retry also fails, Flipper::Adapters::FirebaseRemoteConfig::ETagMismatch is raised.

If you have a write-heavy multi-process workload that frequently conflicts, this adapter is the wrong tool.

• Remote Config conditions. Firebase Remote Config has a powerful conditional value system (per-platform, per-country, per-user-property). v0.1 ignores it: every gate is stored as the parameter's defaultValue only. If you change a parameter's conditionalValues in the Firebase console, the adapter will not see those changes. Conditions may be exposed as a Flipper extension in a future release; PRs welcome.
• Server-side caching beyond the adapter's in-process TTL. Combine with Flipper::Adapters::Memoizable and ideally a longer-lived cache (Redis, Memcached) for high-traffic apps.

The Firebase Remote Config v1 API does not have a generated Ruby client gem (google-apis-firebaseremoteconfig_v1 is not published to RubyGems, and the deprecated umbrella google-api-client does not include it either). So the two REST calls we actually need (GET + PUT on /v1/projects/{id}/remoteConfig) go through Net::HTTP directly. Auth is real: we depend on googleauth for the OAuth2 service-account flow. See CLAUDE.md for the longer story.

bundle install
bundle exec rspec
bundle exec rubocop

Bug reports and pull requests are welcome on GitHub at https://github.com/devops-health/flipper-firebase_remote_config. See CONTRIBUTING.md for dev setup and PR guidelines.

For security issues, please follow SECURITY.md rather than opening a public issue.

Released under the MIT License.