Golang Microservices Full Course #13 - Redis Caching

Summary

This episode of the Go microservices course introduces Redis caching—using the rate/read-through cache plus the cache-aside pattern—to speed up wallet balance reads. It also explains cache invalidation when underlying MySQL data changes (for example, after transfers).

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Goals / Problem Solving

• Replace direct DB reads with an in-memory Redis cache backed by MySQL.
• Implement cache-aside behavior:
  • Try Redis first.
  • On cache miss: query MySQL, then store the result in Redis.
• Handle cache invalidation:
  • When wallet balances change (e.g., after a transfer), delete the relevant Redis cache keys so future reads fetch fresh data from MySQL.

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Caching Flow Implemented

In the wallet service handler (example mentioned: /wallets/me):

1. Build a Redis cache key, such as:
   • wallet:{userId}
   • Constructed via fmt.Sprintf using the user ID.
2. Check Redis:
   • If found: deserialize JSON into the wallet model and return immediately.
   • If not found: fetch wallet from MySQL, serialize it, and store it in Redis.
3. TTL (time-to-live):
   • Set Redis key expiration to ~5 minutes (e.g., EXPIRE / Set(..., 5 minutes)).

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Redis + Docker Compose Setup

• Add Redis to docker-compose.yml alongside MySQL:

  • Image: redis:7-alpine
  • Container name: go-wallet-redis
  • Port mapping: 6379:6379
  • Restart policy: always

• Update Go dependencies and configuration:

  • Uses github.com/ra/go-redis v9
  • Set Redis host/port via internal config:
    • radius/redis address built from environment host + port.

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Redis Client Wrapper / Connection Logic

• Create a Redis “database wrapper” under internal/database/...:
  • Connect to Redis using the configured address.
  • Use a context with timeout (subtitles mention ~3 seconds).
  • Log a successful connection via an internal logger.

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Cache Invalidation After Transfers

Redis cache keys must be deleted whenever balances change.

• Implemented in the transaction commit / after-transfer flow:
  • After a transfer commits, invalidate:
    • Sender’s wallet cache key
    • Receiver’s wallet cache key
  • Delete keys using Redis DEL (e.g., via Del).

Performance Detail

• Cache deletion should be asynchronous / non-blocking so it does not delay the HTTP response.

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Testing / Mocks (Unit Tests)

• Mocks are updated to include Redis expectations:
  • Transaction service tests require mocking Redis client behavior for cache invalidation.
• Test cases are added/updated so invalidation behavior is validated.
• Notes include potential test panics when dependencies (such as logger and Redis client) are not correctly included/mocked.

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Runtime Verification / Expected Results

Manual testing is done using Swagger endpoints (course mentions running Swagger via go run ... swagger, including routes like register/profile/get-my-profile).

Expected behavior

• First request to wallets/me:
  • cache miss → fetch from MySQL → store to Redis
• Second request:
  • cache hit → return from Redis

Log messages

• “cache miss … falling back to my SQL”
• “cache hit … returning from radius/Redis”

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Main Speakers / Sources

• Course/author name is not explicitly stated in the subtitles.
• Referenced external libraries:
  • Redis client library: github.com/ra/go-redis/v9
• Project components mentioned:
  • Swagger/OpenAPI tooling
  • “Go wallet” microservices codebase (wallet + transaction services)