"Premature optimization is the root of all evil." However, in cloud migrations, the abstraction of resources often hides the physical limitations of the underlying hardware. For latency-sensitive legacy runtimes, these abstractions can become a performance bottleneck. This post analyzes a migration of a legacy .NET Framework 4.8.1 monolith from standalone EC2 instances to Windows Containers on AWS ECS , where the choice of Fargate led to a 10x performance degradation. 1. The Context: Infrastructure Modernization The primary goal was to achieve centralized deployment and orchestration using AWS ECS. The Constraints: A migration to .NET 6+ was rejected due to cost and time constraints. The mandate was to containerize the existing .NET 4.8.1 codebase "as-is." The Path: Migration from legacy EC2 setups to Windows Containers on ECS Fargate. The Stack: .NET 4.8.1, Razor Pages, Windows Server Core images. 2. The Symptom: Consistent 20-Second Latency Post-migration, page rendering latency spiked to 20 seconds .…