An API gateway is a single-entry point for all application programming interface (API) calls made by client devices to a particular set of backend services, such as containerized web applications within a Kubernetes cluster. The API gateway sits directly between desktop and mobile clients and the different services they are trying to connect to.

The API gateway functions as a reverse proxy that fetches and aggregates appropriate resources before delivering a response to each API request. At the same time, it can perform multiple actions including IP filtering, token-based API authentication, rate limiting, and integration of web application firewall (WAF) functionality—all to support secure and reliable access to APIs as well as to microservices.