Monitoring is an essential part of a modern production system. If you can't monitor a service, you don't know what's happening, and if you’re blind to what's happening, your service can’t be reliable. In this excerpt from O'Reilly's book Site Reliability Engineering, you'll learn how and what to monitor, using implementation-agnostic best practices. Author Rob Ewaschuk explains basic principles and best practices that he and other members of Google’s Site Reliability Engineering (SRE) teams use for building successful monitoring and alerting systems. You'll learn guidelines for determining which issues are serious enough to involve human intervention, and how to deal with issues that aren’t. Complete with case studies describing monitoring efforts with Bigtable and Gmail, this article helps you ask the right questions--regardless of your organization's size or the complexity of your service or system.