feat(zoneproxies): check empty listeners

[jakubdyszkiewicz]

Checklist prior to review

I noticed that sometimes in e2e test we end up in this situation

[2023-08-21 20:32:22.374][81][warning][config] [source/extensions/config_subscription/grpc/grpc_subscription_impl.cc:128] gRPC config for type.googleapis.com/envoy.config.listener.v3.Listener rejected: Error adding/updating listener(s) inbound:172.18.0.10:30686: error adding listener '172.18.0.10:30686': no filter chains specified

[2023-08-21 20:32:22.374][81][info][upstream] [source/common/upstream/cds_api_helper.cc:32] cds: add 3 cluster(s), remove 2 cluster(s)
[2023-08-21 20:32:22.383][81][info][upstream] [source/common/upstream/cds_api_helper.cc:69] cds: added/updated 1 cluster(s), skipped 2 unmodified cluster(s)
[2023-08-21 20:32:27.402][81][warning][config] [source/extensions/config_subscription/grpc/grpc_subscription_impl.cc:128] gRPC config for type.googleapis.com/envoy.config.listener.v3.Listener rejected: Error adding/updating listener(s) inbound:172.18.0.10:30686: error adding listener '172.18.0.10:30686': no filter chains specified

which means that this if for adding empty filter chain match does not work. It's not clear to me how to reproduce it and under what condition this happens, but we can at least fix the condition so we won't send listener without filter chains.

• Link to relevant issue as well as docs and UI issues -- trying to fix flaky multizone test
• This will not break child repos: it doesn't hardcode values (.e.g "kumahq" as a image registry) and it will work on Windows, system specific functions like syscall.Mkfifo have equivalent implementation on the other OS --
• Tests (Unit test, E2E tests, manual test on universal and k8s) --
• Do you need to update UPGRADE.md? --
• Does it need to be backported according to the backporting policy? (this GH action will add "backport" label based on these file globs, if you want to prevent it from adding the "backport" label use no-backport-autolabel label) --
• Do you need to explicitly set a > Changelog: entry here or add a ci/ label to run fewer/more tests?

[michaelbeaumont]

For some reason I remember @bartsmykla saying this was intentional, or maybe a comment somewhere? I think it can happen in

kuma/pkg/xds/generator/zoneproxy/generator.go

Line 85 in 7959651

func AddFilterChains(

pretty easily, when there are no destinations

[jakubdyszkiewicz]

Intentional? But we should not send invalid config to envoy

[michaelbeaumont]

Yeah I agree, can we handle it in AddFilterChains?

[jakubdyszkiewicz]

how could we handle this in AddFilterChains?

[bartsmykla]

For some reason I remember @bartsmykla saying this was intentional, or maybe a comment somewhere?

I unfortunately don't remember it