Ingress controller vs api gateway

Ingress controller allows single ip-port to access all services running in k8s through ingress rules. The ingress controller service is set to load balancer so it is accessible from public internet.

An api gateway is used for application routing, rate limiting, security, request and response handling and other application related tasks. Say, you have a microservice based application in which the request needs an information to be collected from multiple micro services. You need a way to distribute the user requests to different services and gather the responses from all micro services and prepare the final response to be sent to the user. API Gateway is the one which does this kind of work for you.

Indeed both have a set of features that intersect, path mapping, path conversion, load balancing, etc.

However, they do differ. I may be wrong, but you create an Ingress 1) to run it in Kubernetes 2) to be more of like a reverse proxy "kubernetes native".

API Gateway could be installed anywhere (although there are now many that run in Kubernetes natively like Ambassador, Gloo, Kong), and they do have more functionality available like developer portal, rate limiting, etc.

Personally I use an ingress as a reverse proxy for a website. And API Gateway for APIs. This does not mean you can't use ingress for apis. However, you are not taking full advantage of them.