API design refers to the process of developing Application Programming Interfaces (APIs) that expose the functionality of software applications to their clients. This paper provides a performance and availability-related analysis of three modern API design techniques, namely Representational State Transfer, Google’s Remote Procedure Call Framework, and Apache Thrift to practically show which of these techniques should be used in the implementation of the API Gateways for performance and availability considering that the gateways undertake a crucial role as they are the backbone of communication in Microservices Architecture and the performance and availability are two critical factors that determine how well API gateways can perform. For our analysis, an API Gateway prototype for each of the three API design techniques was developed by using Microsoft’s.NET framework, and load-tests against each of these three prototypes were performed and analyzed. The results of this paper are expected to be helpful for both researchers and practitioners in the software industry who need to choose from different industrial API design techniques for API Gateway development.