Single-worker Flask/FastAPI apps degrade severely under concurrent load

Flask/FastAPI applications without configured worker processes show severe performance degradation under concurrent load. Response times can increase from 14ms (single request) to 1.6s+ with 500 concurrent users, continuing to climb. Each worker handles only one request at a time, creating a processing bottleneck.

Configure multiple worker processes using the --workers parameter at server initialization. For single CPU instances (e.g., Cloud Run), use 4 workers; for multi-core machines (e.g., 6-core), use up to 16 workers. Calculate worker count based on available CPU cores and application memory consumption patterns.