Why ASP.NET Core Feels Fast Locally but Slow in Production

ASP.NET Core applications often run fast locally but slow in production due to environment differences, resource constraints, database query inefficiencies, async/await misuse, excessive logging, cold starts, improper caching, and network latency. The guide covers common bottlenecks like EF Core N+1 queries, thread pool starvation from blocking calls, logging overhead, in-memory cache limitations in scaled environments, and HttpClient socket exhaustion. It provides code examples showing problematic patterns versus optimized alternatives, emphasizing measurement-driven optimization: timing requests and database queries, checking thread pool health, reducing allocations, and implementing distributed caching before scaling infrastructure.