HLD-103·Caching & Edge
Easy · 500 ptsGlobal Feature Flag & Dynamic Config Service
Design a configuration and feature-toggle distribution backend polled by backend and mobile SDKs during coordinated app rollouts.
Max p99
≤ 25 ms
Availability
≥ 99.5%
Budget
≤ $1,900
Functional Requirements
- FR-1GET /v1/flags/{env_id} — Fetches compiled flag evaluation ruleset for an environment.
- FR-2POST /v1/flags/{env_id} — Creates or publishes updated targeting percentages and kill-switch overrides.
- FR-3DELETE /v1/flags/{env_id}/{flag_key} — Archives or disables retired flags and propagates cache eviction across SDK tiers.
- FR-4SDK evaluations must remain available even if the primary config database crashes.
Workload Profile
Baseline SDK Polls22,000 Read RPS / 400 Config Write RPS
Release Rollout Peak60,000 Read RPS / 1,000 Write RPS
Active Working Set6 GB active flag rulesets
Traffic DistributionHeavy read concentration on production env_id keys
Consistency Model
Eventual propagation (< 5s) to edge/cache tiers acceptable; flag rule mutations must be durably stored.
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