Checkout suddenly got a lot slower for a chunk of users, and the only clue was a spike in an application metric. In this walkthrough, we go from that spike to a linked trace that shows exactly where the time went. Using Codex alongside Sentry, we dig into the trace data, isolate the slowdown to the European backend, and follow it down to a single Stripe request that's dragging everyone down with it. Along the way, we talk through what actually helps here: caching, timeouts, async calls, and other ways to keep one slow dependency from becoming everyone's problem.
