Amazon EC2′s high-profile outage in the US East region has taught us a number of lessons. For many, the take-away has been a realization that cloud-based systems (like conventionally-hosted systems) can fail. Of course, we knew that, Amazon knew that, and serious companies who performed serious availability engineering before deploying to the cloud knew that. In cloud environments, as in conventionally-hosted environments, you must implement high-availability if you want high availability. You can’t just expect it to magically be highly-available because it is “in the cloud.” Thorough and thoughtful high-availability engineering made it possible for EC2-based Netflix to experience no service interruptions through this event.