We spend a lot of time gathering metrics for our network, servers, and many things going on within the code that drives Etsy. It’s no secret that this is one of our keys to moving fast. We use a variety of monitoring tools to help us correlate issues across our architecture. But what most monitoring tools achieve is correlating the effects of change, rather than the causes.
Change to application code (deploys) are opportunities for failure. Tweaking pages and features on your web site cause ripples throughout the metrics you monitor, including database load, cache requests, web server requests, and outgoing bandwidth. When you break something on your site, those metrics will typically start to skew up or down.