The role of limitations and SLAs in the API industry

As software architecture design is evolving to a microservice paradigm, RESTful APIs are being established as the preferred choice to build applications. In such a scenario, there is a shift towards a growing market of APIs where providers offer different service levels with tailored limitations typically based on the cost. In this context, while there are well established standards to describe the functional elements of APIs (such as the OpenAPI Specification), having a standard model for Service Level Agreements (SLAs) for APIs may boost an open ecosystem of tools that would represent an improvement for the industry by automating certain tasks during the development such as: SLA-aware scaffolding, SLA-aware testing, or SLA-aware requesters. Unfortunately, despite there have been several proposals to describe SLAs for software in general and web services in particular during the past decades, there is an actual lack of a widely used standard due to the complex landscape of concepts surrounding the notion of SLAs and the multiple perspectives that can be addressed. In this paper, we aim to analyze the landscape for SLAs for APIs in two different directions: i) Clarifying the SLA-driven API development lifecycle: its activities and participants; 2) Developing a catalog of relevant concepts and an ulterior prioritization based on different perspectives from both Industry and Academia. As a main result, we present a scored list of concepts that paves the way to establish a concrete road-map for a standard industry-aligned specification to describe SLAs in APIs.