Accessing resolved address for client instrumentation

[Brett Harvey]

Hi all,

I'm exploring ways to enrich tracing data from my gRPC clients with the resolved IP address to which an RPC is sent. This is particularly important in scenarios where there is a reverse proxy in front of the backends and the set of peer IPs seen in the backends' ServerContexts is distinct from the set of IPs resolved on the client side. Such scenarios can arise when an internet-facing load balancer serves traffic to non-publicly accessible backends.

I am specifically looking to access this information from within a Client Interceptor. My clients are written in Ruby, but I'm also interested in understanding if this is possible in C++. If directly accessing resolved IP addresses within a Client Interceptor is not possible, I'm open to suggestions on alternative approaches to capturing this information.

My initial approach was to use the `peer` attribute of an `ActiveCall` but this turns out to be just the unresolved DNS name.

Thank you in advance for your help and for your ongoing efforts in maintaining this powerful library and its community.

Best,

Brett