Enable HTTP/2 between proxies even when the service protocol is HTTP/1.1

[lobkovilya]

Description

Today, we generate outbound cluster with HTTP/1.1 if the appProtocol: http

kuma/pkg/plugins/policies/core/xds/meshroute/clusters.go

Lines 87 to 88 in 2868538

	case core_meta.ProtocolHTTP:
	edsClusterBuilder.Configure(envoy_clusters.Http())

at the same time we generate inbound HCM with AUTO

kuma/pkg/xds/envoy/listeners/v3/http_connection_manager_configurer.go

Line 23 in fa3eb62

CodecType: envoy_hcm.HttpConnectionManager_AUTO,

so the resulting protocol is HTTP/1.1.

There’s an advantage to using HTTP/2 between proxies since it allows multiple HTTP streams to share a single TCP connection, improving connection reuse and efficiency.

[lukidzi]

Based on the code, it seems that we only generate this for ExternalServices. As you can see the protocol is set to HTTP/2 only if the service type is different from ExternalService.

kuma/pkg/plugins/policies/core/xds/meshroute/clusters.go

Line 96 in 2868538

Configure(envoy_clusters.Http2())

)

[lobkovilya]

Ah, so I looked at the wrong line, it's not an issue for service-to-service then. Not sure if we need to change it for external services