The performance and scalability of an API gateway application are very important because they are both single points that all client requests pass. With that in mind, we need to consider asynchronous and non-blocking I/O platforms when building an API gateway application. There are many platforms that provide these asynchronously, including non-blocking I/O platforms such as Netty, Vertx, Spring Reactor, and JBoss Undertow.
https://aws.amazon.com/blogs/aws/amazon-api-gateway-build-and-run-scalable-application-backends/