Explains when to choose feature flags, its trade-offs, prerequisites, warning signs, and viable alternatives. This reference fixes the adoption boundary, failure behavior, and observable evidence while leaving environment-specific limits configurable.
Package status: reference context ready for human review. The contract and test scenarios are complete, but no claim is made that an adopting implementation has passed them.
Decision
For Feature flags, adopt a recorded architecture decision with owned interfaces and dependency direction. Record the choice, drivers, prerequisites, alternatives, trade-offs, reversibility, and invalidation signals before implementation begins. This package is a reference contract: the adopting team must choose numeric limits, providers, jurisdictions, and operational owners from evidence in its own environment.
Scope
- The Feature flags actors, inputs, outputs, states, policy or schema versions, and externally visible outcomes described by this decision block.
- Primary and alternate interfaces, background work, caches, integrations, support paths, and evidence that can exercise the same boundary.
- Adoption-specific configuration, rollout, recovery, and verification responsibilities needed to apply the reference safely.
Outside this block
- Choosing a universal vendor, framework, jurisdiction, numeric threshold, retention period, or service-level objective for every adopter.
- Claiming that packaged scenarios have run against a downstream implementation or that this reference grants legal, security, or accessibility certification.
Contract
- Name the decision drivers, alternatives, constraints, reversibility, and conditions that would invalidate the chosen structure.
- Assign data, behavior, interface, deployment, and operational ownership at every boundary; shared code does not erase ownership.
- Permit dependencies only in the documented direction and exchange stable contracts rather than another component's internal model.
- Define timeout, capacity, consistency, degradation, deployment, migration, and recovery behavior for each remote or asynchronous boundary.
- Tie the choice to observed scale and organizational constraints rather than fashion or a hypothetical future load.
- Name the smallest reversible experiment that would reduce the largest remaining uncertainty.
- Give every flag an owner, purpose, scope, safe default, creation and expiry dates, evaluation evidence, and removal issue rather than treating it as permanent configuration.
- Evaluate sensitive flags with authenticated server context, version changes, test both states, bound rollout, and remove code and stored branches after the decision closes.
Implementation guidance
- Score viable alternatives against the same drivers and keep rejected options with the reason and review trigger.
- Model Feature flags inputs, outputs, actors, states, invariants, side effects, and evidence before selecting framework or vendor details.
- Store the applicable Feature flags contract or policy version with material state so migrations, replay, and support decisions remain attributable.
- Introduce the path behind controlled rollout, compare expected and observed outcomes, and keep a tested recovery route until adoption evidence is complete.
Failure handling and safeguards
- A boundary failure remains contained, produces a stable caller outcome, and has a tested rollback or forward-recovery path.
- Invalid or contradictory Feature flags state is rejected or quarantined; the implementation never guesses a value that broadens authority or duplicates an effect.
- Retries are bounded and use durable identity; after exhaustion, work reaches an inspectable terminal state with an accountable owner.
Verification and operations
- Review the decision after a representative implementation slice and whenever an invalidation signal crosses its agreed boundary.
- Monitor Feature flags success, denial, validation failure, dependency failure, retry exhaustion, and recovery by contract version without sensitive payload dimensions.
- Re-run paired positive and negative fixtures after policy, schema, dependency, migration, or boundary changes and preserve the resulting evidence.
Adoption assumptions
- Names and values in the example are a concrete fixture, not universal defaults; adopters replace them through documented evidence and ownership.
- The adopting system can provide authenticated identity, durable operation or record versions, bounded telemetry, and a controlled path for change.
The executable-looking examples in this package are fixtures and acceptance contracts. Run the collection validator to check structure and metadata, then translate and execute the scenarios in the target repository before recording implementation evidence.