User Story
As an API consumer, I need faster response times for frequently accessed, relatively static data endpoints (currencies, institutions, and public key), so that the application performs more efficiently and reduces unnecessary load on our backend services.

Acceptance Criteria

1. GIVEN a request is made to /currencies endpoint
   WHEN the cache is empty or expired
   THEN fetch from source and cache the response for 24 hours
   AND return the response

2. GIVEN a request is made to /institutions/:currency_code
   WHEN the cache is empty or expired for that currency code
   THEN fetch from source and cache the response for 24 hours
   AND return the response

3. GIVEN a request is made to /pubkey
   WHEN the cache is empty or expired
   THEN fetch from source and cache the response for 1 year
   AND return the response

4. GIVEN a request is made to any of these endpoints
   WHEN valid cached data exists
   THEN return the cached response without hitting the backend

5. GIVEN the application is starting up
   WHEN the server initializes
   THEN automatically fetch and cache all static data (currencies, institutions for supported currencies, pubkey)
   AND log the cache warming status for monitoring

Tech Details

• Implement caching using Redis with the following keys:

api:currencies:list
api:institutions:{currency_code}
api:aggregator:pubkey

• Implementation requirements:
  • Add Redis cache middleware for the specified routes
  • Implement cache key generation based on endpoint and parameters
  • Add cache headers in response (Cache-Control, ETag)
  • Add monitoring for cache hit/miss rates
  • Handle cache failures gracefully (fallback to direct response)

Notes/Assumptions

• Redis is already available in the infrastructure
• Cache durations are configurable via environment variables
• Cache keys should include version prefix for future updates
• Response includes appropriate cache headers
• Implement stale-while-revalidate pattern for high availability

Open Questions

• Should we implement batch cache invalidation?