feat.so

feat Ruby SDK

Server-side Ruby SDK for feat feature flags. Local flag evaluation against a live-streamed datafile. Standard library only - no gem dependencies.

Install

# Gemfile
gem "feat-sdk"

bundle install

Ruby 3.0+.

Usage

require "feat"

client = Feat::Client.new(
  api_key: ENV.fetch("FEAT_SERVER_KEY"),
  url: "https://data-01.feat.so", # optional; this is the default
)
client.start

ctx = {
  targetingKey: "user-123",
  user: { plan: "pro", email: "alice@example.com" },
}

if client.get_boolean_value("checkout-v2", false, ctx)
  # ...
end

client.close

Use a server API key (feat_sdk_...).

How it works

  • Fetches a per-environment datafile and keeps it in memory.
  • Streams updates over Server-Sent Events: a background thread holds an open connection and applies each new datafile the instant it changes. Updates are version-ordered (an older or equal datafile is never adopted) and guarded by a mutex shared with the evaluator.
  • Keeps a slow background poll (every 5 minutes by default) as a safety net. ETag-aware via If-None-Match. If the stream drops, it reconnects with exponential backoff while the poll keeps the datafile fresh.
  • Evaluation runs in-process: no per-flag network call.
  • close stops the stream and poll threads cleanly.

Streaming options

Streaming is on by default. To disable it and rely on polling alone:

client = Feat::Client.new(
  api_key: ENV.fetch("FEAT_SERVER_KEY"),
  streaming: false,        # poll-only mode
  poll_interval: 30,       # seconds (used when streaming is off)
)

When streaming is on, safety_poll_interval: (default 300 seconds) controls the backstop poll cadence.

License

MIT