Building Reliable Feature Flags & Progressive Delivery Pipelines

Progressive delivery reduces blast radius while turning releases into measurable experiments. Feature flags are infrastructure for learning, not just on/off switches.

Flag Taxonomy

• Release Flags: Gradual exposure of new code paths.
• Experiment Flags: A/B or multivariate branches tied to KPI evaluation.
• Ops Kill Switches: Rapid disable for unstable integrations.

Operational Guardrails

1. TTL every flag; stale flags auto‑reported.
2. Ownership metadata (team, purpose) required at creation.
3. Telemetry: flag state included in trace/span attributes.

Example Evaluation Wrapper

export function withFlag(flag: string, fallback: () => any, enabled: () => any) {
	const active = flagClient.isEnabled(flag);
	trace.setAttribute('flag.' + flag, active);
	return active ? enabled() : fallback();
}

Rollout Stages

• Internal (dogfood) → 5% → 25% → 50% → 100%.
• Abort if error budget consumption spikes or KPI regression >= agreed threshold.

Common Failure Modes

• Unbounded growth of stale flags → increases cognitive load.
• Flag logic scattered → centralize evaluation helpers.
• Lack of observability → decisions become guesswork.

Disciplined flag hygiene compounds speed and safety.