Support for connection via UNIX Domain Socket(UDS) when sending trace spans from istio-proxy to Datadog Agent.

[mugioka]

Describe the feature request

Currently, we are unable to configure the Unix Domain Socket (UDS) to send tracing spans to Datadog. This limitation arises from the DataDogAddress function which only accepts values in the host:port format. Moreover, the Istiod-generated configuration below does not support UDS:

{
    “name”: “datadog_agent”,
    “type”: “STRICT_DNS”,
    “connectTimeout”: “1s”,
    “loadAssignment”: {
        “clusterName”: “datadog_agent”,
        “endpoints”: [
            {
                “lbEndpoints”: [
                    {
                        “endpoint”: {
                            “address”: {
                                “socketAddress”: {
                                    “address”: “datadog.example.svc.cluster.local”,
                                    “portValue”: 8126
                                }
                            }
                        }
                    }
                ]
            }
        ]
    },
    “respectDnsTtl”: true,
    “dnsLookupFamily”: “V4_ONLY”
}

From my understanding of the Envoy configuration, config.core.v3.SocketAddress does not support UDS. Therefore, we need to use config.core.v3.Pipe to send the tracing span via UDS.

Datadog supports UDS for receiving trace spans. Therefore, we would like to support that send trace spans via UDS to optimize the performance of traceable Istio-proxy.

Describe alternatives you've considered

Affected product area (please put an X in all that apply)

[ ] Ambient
[ ] Docs
[ ] Dual Stack
[ ] Installation
[ ] Networking
[ x ] Performance and Scalability
[ ] Extensions and Telemetry
[ ] Security
[ ] Test and Release
[ x ] User Experience
[ ] Developer Infrastructure

Affected features (please put an X in all that apply)

[ ] Multi Cluster
[ ] Virtual Machine
[ ] Multi Control Plane

Additional context

[mugioka]

Envoy internally uses Datadog integration for C++. Therefore, in order to send tracing spans to the Datadog agent via UDS (Unix Domain Socket), modifications are required to both Envoy and the Datadog C++ tracing library.

https://github.com/envoyproxy/envoy/blob/main/source/extensions/tracers/datadog/README.md

[mugioka]

https://github.com/DataDog/dd-trace-cpp/blob/main/src/datadog/http_client.cpp

Datadog cpp lib supports unix domain sockets.

[zirain]

need envoy support this first.