refactor(cache): improve redis connection handling for serverless

Add lazy connection with timeouts and better environment detection to prevent startup crashes in serverless environments. Fallback to in-memory cache when Redis is unavailable or misconfigured.

Author: samdevtx

backend/app/cache.py

@@ -9,16 +9,37 @@
 WEATHER_CACHE_TTL = 600
 GEOCODING_CACHE_TTL = 3600
 
-# Redis Connection
-redis_url = os.getenv("REDIS_URL", "redis://localhost:6379/0")
-try:
-    redis_client = redis.from_url(redis_url, decode_responses=True)
-    # Test connection
-    redis_client.ping()
-    logger.info(f"Connected to Redis at {redis_url}")
-except Exception as e:
-    logger.warning(f"Failed to connect to Redis: {e}. Fallback to in-memory cache.")
-    redis_client = None
+# Redis Connection Setup
+# We do NOT connect or ping here to avoid startup crashes in Serverless environments
+# if the Redis URL is invalid or unreachable (e.g. localhost in Vercel).
+
+redis_url = os.getenv("REDIS_URL", "")
+redis_client = None
+
+# Determine if we should attempt Redis connection
+# In Vercel, if REDIS_URL is missing or is localhost, we skip directly to memory cache
+should_use_redis = bool(redis_url and "localhost" not in redis_url)
+
+if os.getenv("IS_DOCKER") or os.getenv("IS_LOCAL"):
+    # Force attempt if explicitly in Docker/Local dev, even if localhost
+    should_use_redis = bool(redis_url)
+
+if should_use_redis:
+    try:
+        # Create client but don't ping immediately (lazy connection)
+        # Socket timeout is critical to avoid hanging the serverless function
+        redis_client = redis.from_url(
+            redis_url, 
+            decode_responses=True, 
+            socket_timeout=2.0,
+            socket_connect_timeout=2.0
+        )
+        logger.info(f"Redis client configured for {redis_url}")
+    except Exception as e:
+        logger.warning(f"Failed to configure Redis client: {e}. Using in-memory cache.")
+        redis_client = None
+else:
+    logger.info("Redis disabled or invalid URL. Using in-memory cache.")
 
 # In-memory fallback
 _memory_cache = {}
@@ -30,6 +51,7 @@ def _get_from_redis(key: str) -> Optional[Any]:
         val = redis_client.get(key)
         return json.loads(val) if val else None
     except Exception as e:
+        # If Redis fails during operation, log and fallback to memory (optional, currently just returns None)
         logger.error(f"Redis get error: {e}")
         return None
 
@@ -41,6 +63,8 @@ def _set_in_redis(key: str, value: Any, ttl: int) -> None:
         redis_client.setex(key, ttl, json.dumps(value))
     except Exception as e:
         logger.error(f"Redis set error: {e}")
+        # Fallback to memory on write failure
+        _memory_cache[key] = value
 
 def get_geocoding_cache(key: str) -> Optional[List[City]]:
     """Get cached geocoding results"""