Mixed IP and UDS endpoints rejected for ExtService

[guydc]

Description:
Envoy allows mixing static endpoints in the same cluster (e.g. IP + UDS). This was supported until EG 1.6.

EG currently rejects this configuration, since it treats UDS as a different address type from IP, as of: #6784, while they are both considered the same for mixed endpoint determination purposes.

[zirain]

will take a look at this later.

[zirain]

This's not supported from the beginning in #3495
#5747 changed the error message
#6784 didn't change the result of IR.

What I missed?

[arkodg]

@zirain

gateway/internal/ir/xds.go

Line 1727 in 42825c7

func (r *RouteDestination) NeedsClusterPerSetting() bool {

kicks in which creates weighted clusters for this case if mixedendpoints are set

[stekole]

I was looking into this issue and trying to understand deeper. I think I have a path forward.

PR #6784 caused the regression, but specifically for ext service backends . For route backends, UDS was never supported AFAICT.
I think we are rejecting in a few places.
check that rejects UDS.
if more than one address type exists in the map, it's unconditionally set to ir.MIXED https://github.com/envoyproxy/gateway/blob/main/internal/gatewayapi/route.go#L2508 and rejected

I am deep in the weeds and wanted to put together a PR. I do not mean to step on any toes. Please Let me know if I am not in the right direction.
#8530