Feature Flags System - Product Requirements Document
Version: 2.0 | Status: Business Review | Date: 2026-01-15
Change Log:
- v2.0 (2026-01-15): Converted to business-focused format with measurable outcomes
- v1.0 (2026-01-09): Initial technical draft
1. Executive Summary
1.1 Purpose
Enable controlled feature releases, subscription-tier differentiation, and zero-downtime infrastructure migrations through centralized feature flag management.
1.2 Problem Statement
Without feature flag capabilities, Toprent.app faces:
- Deployment risk: All-or-nothing releases affect 100% of users immediately
- Revenue leakage: No enforcement mechanism for subscription tier features
- Migration risk: Database transitions require big-bang cutover with rollback complexity
- Slow feedback cycles: Features cannot be tested with subset of users before full release
1.3 Business Value
| Value Area | Measurable Outcome | Target |
|---|---|---|
| Risk Mitigation | Reduce deployment-related incidents requiring rollback | 80% reduction within 6 months |
| Revenue Protection | Enforce feature access by subscription tier | 100% compliance, zero unauthorized access |
| Operational Continuity | Enable database migrations without scheduled downtime | Zero downtime during Fauna→PostgreSQL migration |
| Market Responsiveness | Reduce time from feature complete to full rollout | From 1 release cycle to gradual rollout capability |
| Development Velocity | Increase deployment frequency by decoupling releases | 2x deployment frequency within 3 months |
1.4 Target Users
| User | Business Context |
|---|---|
| Product Managers | Control feature rollouts, run pilots with specific customer segments |
| Platform Administrators | Manage infrastructure migrations, respond to production issues instantly |
| Tenant Administrators | Receive correct feature access based on subscription plan |
| End Users | Experience consistent features throughout their session |
1.5 Scope
In Scope:
- Centralized feature flag management via third-party platform
- Server-side and client-side flag evaluation
- Subscription plan-based feature gating
- Migration flags for database transitions
- Gradual rollout capabilities
- Consistent user experience across sessions
Out of Scope:
- A/B testing and experimentation framework
- Custom flag management UI within Toprent.app
- Self-service flag creation by non-technical users
- Real-time flag updates (5-minute refresh acceptable)
2. Success Metrics
| Metric | Definition | Baseline | Target | Measurement Method | Timeframe |
|---|---|---|---|---|---|
| Deployment Incidents | Rollbacks required due to feature issues | 4/month (est.) | <1/month | Incident tracking system | 6 months post-launch |
| Feature Compliance Rate | % of feature access correctly enforced by plan | Manual enforcement | 100% automated | Access audit logs | Ongoing |
| Migration Downtime | Scheduled downtime for database migrations | 4+ hours per migration | 0 hours | Migration runbook tracking | Per migration |
| Rollout Control | Ability to target specific user percentages | 0% (all-or-nothing) | 1-100% granularity | Flag platform dashboard | Immediate |
| Incident Response Time | Time to disable problematic feature | 30+ min (deploy required) | <5 min | Incident response logs | Ongoing |
| Deployment Frequency | Production deployments per week | 3/week | 6/week | CI/CD metrics | 3 months post-launch |
| Flag Evaluation Latency | Time to check feature flag | N/A | <10ms (server), 0ms (client cached) | Performance monitoring | Ongoing |
3. User Stories
Product Manager
| Priority | Story | Acceptance Criteria |
|---|---|---|
| P0 | As a product manager, I want to enable features for a percentage of users, so I can validate before full rollout | Given a new feature flag, when I set rollout to 10%, then exactly 10% of users see the feature consistently |
| P0 | As a product manager, I want premium features restricted to paid plans, so free users cannot access paid functionality | Given a premium feature, when a free-tier user attempts access, then the feature is hidden or blocked |
| P1 | As a product manager, I want to target features to specific tenants, so I can run controlled pilots | Given a feature flag with tenant targeting, when I add tenant IDs, then only those tenants see the feature |
| P1 | As a product manager, I want users to see consistent features during their session | Given a user’s flag values, when they navigate the app, then flag values remain stable until next refresh cycle |
Platform Administrator
| Priority | Story | Acceptance Criteria |
|---|---|---|
| P0 | As a platform admin, I want to migrate database entities incrementally, so I minimize risk during transitions | Given a migration flag, when enabled for an entity, then queries use the new database; when disabled, they use the original |
| P0 | As a platform admin, I want to disable features instantly without deployment, so I can respond to production issues | Given a problematic feature, when I disable its flag in the dashboard, then users stop seeing the feature within 5 minutes |
| P1 | As a platform admin, I want flags to refresh automatically, so changes propagate without user action | Given a flag change, when 5 minutes elapse, then all active sessions reflect the new value |
| P1 | As a platform admin, I want to enable maintenance mode globally | Given maintenance mode flag enabled, when users access the app, then they see maintenance notification |
Tenant Administrator
| Priority | Story | Acceptance Criteria |
|---|---|---|
| P0 | As a tenant admin, I want features based on my subscription plan | Given my plan tier, when I access the app, then I see exactly the features included in my plan |
| P1 | As a tenant admin, I want immediate access to new features when I upgrade | Given a plan upgrade, when the change processes, then new features are available on next page load |
4. Functional Requirements
| ID | Requirement | Priority | Business Rationale |
|---|---|---|---|
| FR-001 | System must evaluate feature flags for any user within 10ms on server, 0ms on client (cached) | P0 | Ensures no perceptible delay in feature rendering |
| FR-002 | System must maintain consistent flag values for a user across their session | P0 | Prevents confusing UX where features appear/disappear |
| FR-003 | System must support boolean flags with configurable default values | P0 | Enables fail-safe behavior when flag service unavailable |
| FR-004 | System must support percentage-based rollouts (1-100% of users) | P0 | Enables gradual releases to minimize risk |
| FR-005 | System must support tenant-specific targeting | P0 | Enables pilot programs and enterprise customization |
| FR-006 | System must enforce subscription plan features automatically | P0 | Protects revenue by preventing unauthorized feature access |
| FR-007 | System must support environment-specific flag values (dev/staging/production) | P0 | Enables testing in non-production environments |
| FR-008 | System must refresh flag values every 5 minutes without user action | P1 | Balances flag freshness with system performance |
| FR-009 | System must degrade gracefully when flag service is unavailable | P1 | Ensures application continues functioning during outages |
| FR-010 | System must support 50+ concurrent migration flags | P1 | Supports entity-by-entity database migration |
| FR-011 | System must prevent page load flicker when checking flags | P1 | Maintains professional user experience |
| FR-012 | System must log flag evaluation failures for troubleshooting | P2 | Enables debugging of flag-related issues |
5. Acceptance Criteria
AC-001: Consistent User Experience
Given a user visits multiple pages during a session
When features are controlled by flags
Then the user sees the same feature availability throughout their session
And features do not appear/disappear unexpectedly
AC-002: Plan-Based Feature Enforcement
Given a tenant has a Basic plan without premium features
When the tenant admin attempts to access a Premium feature
Then the feature is not visible or displays upgrade prompt
And no workaround allows access to restricted features
AC-003: Instant Feature Disable
Given a feature is causing production issues
When the platform admin disables the flag in the management dashboard
Then users stop seeing the feature within 5 minutes
And no code deployment is required
AC-004: Migration Flag Control
Given a database migration flag is enabled for “clients” entity
When the application queries client data
Then queries use the new database
And when the flag is disabled, queries automatically revert to the original database
And no downtime occurs during the switch
AC-005: Graceful Degradation
Given the flag management service is unavailable
When the application needs to evaluate a flag
Then the configured default value is returned
And the application continues functioning normally
And errors are logged for operational awareness
AC-006: Percentage Rollout Accuracy
Given a feature flag is set to 25% rollout
When 1000 unique users access the feature
Then approximately 250 users (±5%) see the feature enabled
And each user consistently sees the same value on repeated visits
6. Business Rules
BR-001: Feature Access Priority
- Subscription plan features take precedence over flag-based features
- If a plan excludes a feature, flags cannot enable it
- If a plan includes a feature, flags can still disable it (for rollouts/issues)
BR-002: Migration Flag Safety
- Migration flags default to disabled (original behavior)
- Both original and new code paths must function until migration verified
- Migration flags remain active for minimum 30 days post-full-rollout
BR-003: Flag Lifecycle
- All flags must have documented purpose and planned removal date
- Flags older than 6 months require review for removal
- Deprecated flags are marked but not immediately removed
BR-004: Environment Segregation
- Each environment (development, staging, production) has independent flag configuration
- Production flag changes require documented approval process
- Test environments can have flags enabled that are disabled in production
7. Dependencies
Upstream Dependencies
| System | Dependency Type | Impact if Unavailable |
|---|---|---|
| Authentication System | User identification for targeting | Flags fall back to anonymous defaults |
| Subscription Management | Plan features for gating | Plan features unavailable, flags still work |
| Third-party Flag Platform | Flag configuration and evaluation | Application uses default values |
Downstream Dependencies
| System | How It Uses Flags |
|---|---|
| All Product Features | Check flags before rendering/executing |
| Database Layer | Migration flags control data source |
| API Endpoints | Server-side flag checks for access control |
8. Non-Functional Requirements
Performance
- Flag evaluation: <10ms server-side, <1ms client-side (cached)
- Flag refresh: Every 5 minutes, non-blocking
- No perceptible impact on page load times
Reliability
- Flag service unavailability must not cause application failures
- Default values ensure deterministic behavior during outages
- 99.9% flag evaluation success rate target
Security
- Flag configuration accessible only to authorized administrators
- Client-side cannot override server-evaluated flags
- No cross-tenant data leakage through flag evaluation
Scalability
- Support evaluation of 100+ concurrent flags
- Support 10,000+ concurrent users without performance degradation
9. Risks and Mitigations
| Risk | Likelihood | Impact | Mitigation |
|---|---|---|---|
| Flag service outage | Low | Medium | Default values ensure continued operation |
| Incorrect flag configuration | Medium | High | Require approval for production changes |
| Stale flags accumulating | Medium | Low | Quarterly flag cleanup reviews |
| Performance degradation from flag checks | Low | Medium | Caching and synchronous evaluation |
10. Glossary
| Term | Definition |
|---|---|
| Feature Flag | Configuration controlling feature visibility, changeable without deployment |
| Feature Gate | Access control based on subscription plan tier |
| Rollout | Gradual release of feature to increasing percentage of users |
| Targeting | Enabling features for specific users, tenants, or segments |
| Migration Flag | Flag controlling which database/system handles specific operations |
| Default Value | Flag value used when flag service is unavailable |
| Flag Refresh | Periodic update of flag values from management platform |
Unresolved Questions
- Flag cleanup ownership: Who owns quarterly flag review process? PM or Engineering?
- Approval workflow: What’s the approval process for production flag changes?
- SLA requirements: What uptime SLA needed from third-party flag platform?
- Audit requirements: Do flag changes need audit trail for compliance?