Istio: Possibly unnecessary additional `Listeners` for inbound traffic

[jkbschmid]

Bug description
When debugging envoy config, Istio creates "a virtual listener per service IP, per each non-HTTP for outbound TCP/HTTPS traffic" (see "Debugging Envoy and Istiod"). However, since Istio 1.4, there is a FilterChain on the "virtualInbound"-listener for each open port that directly contains a Route to the correct Cluster.

Therefore, it seems as though inbound traffic is not distributed to these "SidecarInboundListeners" anymore (that's how they're called in the code).

(This very cool DeepDive by @rootsongjc also describes this behaviour and gives some examplary envoy config that is very similar to the one I saw.)

Is there a reason why Istio still creates "SidecarInboundListeners" or can these be removed?

Steps to reproduce the bug
Deploy bookinfo and look at envoy config.

Version
Istio 1.4+

[howardjohn]

This should be fixed on 1.6 by https://github.com/istio/istio/pull/22788

[jkbschmid]

Great to hear, thanks for the quick response!