Start here. This is the direct spoken answer to practice first.
Overview
A slow or throttled provider can exhaust application resources long before it becomes fully unavailable.
I first contain load by limiting admission, disabling unnecessary retries or fan-out, protecting critical traffic, and activating a tested degraded path. Then I trace one affected request and inspect provider latency, throttling, timeouts, retry count, queue age, worker occupancy, connection pools, and cancellation. The goal is to find where downstream slowness became local saturation.