Feature Flags & Remote Config

Since you can't roll back a binary, ship features dark and enable them remotely: feature flags (per user/segment/percentage), remote config (copy, limits, URLs) and kill switches. Evaluate flags server-side where possible (the API simply returns or omits features) or deliver a signed, cached flag snapshot to clients with sane offline defaults. OpenFeature provides a vendor-neutral SDK API.

Where to evaluate flags

import { OpenFeature } from "@openfeature/server-sdk";

const flags = OpenFeature.getClient();
app.get("/v1/home", async (req, res) => {
  const ctx = { targetingKey: req.user.id, appVersion: req.appVersion, platform: req.platform };
  const showReorder = await flags.getBooleanValue("home-reorder-card", false, ctx);
  res.json({ sections: buildHome(req.user, { showReorder }) });
});

// Always have a safe default if config can't be fetched.
val maxUploadMb = remoteConfig.getLong("max_upload_mb").takeIf { it > 0 } ?: 25L
if (remoteConfig.getBoolean("kill_new_checkout")) showLegacyCheckout() else showNewCheckout()

Common pitfalls

• Flags that are never removed (permanent complexity).
• No default when config fetch fails.
• Flag explosion with no owner or expiry.

Key points

• Ship dark, enable remotely
• Kill switches for risky features
• Owners and expiry dates for flags

Further reading: OpenFeature