[andreasarf]

Summary

First of three Redis PRs: cache, then lock (Redisson), then rate limiter (Redisson). This one adds Spring Cache backed by Spring Data Redis (Lettuce), Boot's standard setup.

Cache	What	TTL
sdlc-systems	SDLC systems by id, read on every create, update and SDLC call	10 min (resourceapi.cache.sdlc-systems-ttl)
external-projects	GET /api/v2/projects/{id}/external answers per SDLC system and external id	5 min (resourceapi.cache.external-projects-ttl)

• External lookups (ExternalProjectService). /external is cached, but "unknown" (404) answers are not, so a project is found as soon as it exists. The background sync bypasses the cache and writes the fresh answer into it (@CachePut).
• Serialization. Values are stored as JSON with type information (GenericJacksonJsonRedisSerializer). Types are restricted to this app's and the JDK's classes, so data planted in Redis can't make the app create arbitrary classes.
• Redis down. Failures are logged and skipped (LoggingCacheErrorHandler), so the API keeps working without the cache.
  • The Redis connect and command timeouts are 500 ms. Lettuce's default command timeout is 60 s, which would stall every cached request during an outage.
• Boot settings kept. Defining a custom RedisCacheConfiguration bean makes Boot drop its spring.cache.redis.* settings, so they are applied explicitly. Without this, the key prefix was silently ignored.
• Local dev. compose.yaml and spring-boot-docker-compose start Redis for ./mvnw spring-boot:run. This isn't packaged in the jar and isn't used by tests.
• Docs. README section on Redis; docs/docker.md shows how to point the images at Redis.

Tests

They run against a real Redis 8 started with Testcontainers: one container per test run, shared by all contexts through RedisTestContainerInitializer (registered in spring.factories). Each context gets its own key prefix, because contexts have separate in-memory databases with overlapping ids.

• CacheIntegrationTest:
  • three /external calls lead to one SDLC request, and the record is read back from Redis as ExternalProject;
  • 404s are not cached;
  • a sync bypasses the cache and refreshes it;
  • SDLC systems are served from the cache as entities;
  • keys carry the context's prefix and a TTL.
• CacheUnavailableTest: with Redis unreachable, /external and POST still work, within the time limit.
• Mutation checks. Each was checked to fail with its fix removed: the error handler, the sync bypass, and the key prefix.

Full suite: 89 tests pass. Tests now need Docker, which GitHub Actions provides.

Test plan

• ./mvnw clean test (89 pass, real Redis)
• ./mvnw spring-boot:run starts Redis from compose.yaml; a POST caches resourceapi::sdlc-systems::2
• CI green (first CI run with Testcontainers)

---

Generated by Claude Code