Istio is for building a service mesh inside your network of microservices. This is about the front facing ingress to get into your services from the internet. It's closer to Ambassador (https://getambassador.io)

Thanks, I tried to describe the different categories in our scope https://gitlab.com/gitlab-com/www-gitlab-com/commit/f48d5d8a...

Ambassador is positioned as API GW instead of ingress controller. Contour is designed to be an ingress controller.

Istio provides a control plane and can be deployed to also provide you with a service mesh with a side car approach. Istio also gives you features like rate limiting, traffic shaping, authentication (tls mutual auth) and metrics out of the box. Contour is meant to solve the ingress problem by using Envoy as a reverse proxy. I think it will primarily be focused on doing that.

Istio comes with its own ingress controller that uses envoy. This is an alternative to ambassador, as already said, or nginx-ingress.

Ambassador is positioned as API GW instead of ingress controller. Contour is designed to be an ingress controller. API GW also acts as ingress controller but has more features than ingress controller to manage the APIs. Contour is comparable to Istio-ingress, nginx ingress controller or HAProxy ingress controller.