Architecting for Scale

Chapter 18. Service-Level Agreements

Expectation management.

That’s what Service Level Agreements are all about. As discussed in Chapter 17, each service has different expectations around it. Many of these expectations are tied to the service tier of the service, but when we look deeper, the expectations are more specific than that.

Service-level agreements (SLAs) as discussed in this book are not about legal or contractual agreements between a company and its customers. Rather, they are agreements between teams and service owners. They provide a mechanism for communicating expectations between services.

What are Service-Level Agreements?

Service-level agreements are a commitment to provide a given level of reliability and performance.

They are used to create a strong contractual relationship between service owners and consumers.

An overnight delivery service, for example, might have an SLA that states it will deliver a package before 9 a.m. the next morning. An airline might have an SLA expressing its ability to deliver baggage within a certain period of time after a flight arrives. A power company might have an SLA that states how fast it will fix power outages after a storm.

Example 18-1. What are SLAs?

Consider the online store application illustrated in Figure 16-4.

Your customers expect the store to be operating when they want to use it—they expect it to be highly available. They also expect that the site will load fast so that they can use it without delay. Further, they ...