This week's 30sec SRE article describes the "Hierarchy of Reliability". Dickerson's Hierarchy of Service Reliability provides a set of principles that an organization can use to define and improve reliability to promote engineering excellence. The idea behind the SRE pyramid is that we can categorize the health of a service in a similar way to how A.Maslow categorized human needs. The most basic elements required by a service are at the bottom of the pyramid, and the elements get more advanced as we move further up the pyramid.

You mature your service by "moving up" in the hierarchy. Likewise, if you decommission a service, you can use the hierarchy by "moving down".