TL;DR: Hosting Plex's API servers in eu-west-1 (Ireland) adds ~200ms of latency for US users because light only travels so fast, and this absolutely matters for interactive applications. Here's the data to prove it.
Let's start with the basics. This analysis is based on a HAR file (HTTP Archive format) — essentially a detailed recording of every single network request your browser makes when loading a page. Think of it as a black box recorder for web traffic. When you open your browser's developer tools and load a page, you can export a HAR file that captures:
- Every URL requested
- How long each phase of each request took (DNS lookup, TCP connection, SSL handshake, server processing, data transfer)