Platform Engineering at Google

Chapter 4. Deep Dive: Reliability

By Bharath Modhipalli & Michelle Brush

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What is Reliability, and Why Does It Matter?

Reliability is one of the fundamental features of any system. It provides the foundation upon which user trust is built. If a system is not reliable, its functionality, speed, and feature set are irrelevant because users cannot depend on the system when it matters.

Traditionally, system reliability has been defined in terms of system uptime.¹ However, defining reliability simply as “uptime”—the percentage of time a system is technically operational—is insufficient for modern distributed systems. A system can be “up” but too slow to be usable, or it might be returning incorrect data. Modern reliability engineering defines reliability as the ability of a system to meet the user’s expectations, consistently and correctly. Determining the threshold for what is “reliable enough” remains a complex undertaking. In consumer products, product management typically sets the baseline ...