Adaptive Multi-Tier Rate Limiter

Design a library for an API Gateway that manages rate limiting across different dimensions: IP, UserID, and API Key. The system must support pluggable algorithms (Token Bucket, Sliding Window) and provide a 'graceful degradation' mode where it switches to a local in-memory cache if the centralized Redis store becomes unresponsive. The design should allow developers to define hierarchical rules (e.g., a global limit per IP and a stricter limit per specific endpoint).