I can give an n=1 anecdote here: the dns resolver used to have hard-coded caching which meant that it would be unresponsive to pod updates, and cause mini 30s outages.
That meant that deploying a service which drained in less than 30s would have a little mini-outage for that service until the in-process DNS cache expired, with of course no way to configure it.
Kuberesolver streams updates, and thus lets clients talk to new pods almost immediately.
I think things are a little better now, but based on my reading of https://github.com/grpc/grpc/issues/12295, it looks like the dns resolver still might not resolve new pod names quickly in some cases.
However, that bug probably isn't specific enough as you've described it, unless you can find the commit causing it (such as via a git bisect https://docs.kernel.org/admin-guide/bug-bisect.html), or come up with a clearer repro.
Alternatively, if you're seeing the issue on a distro-maintained kernel (such as on fedora/ubuntu/debian with their kernel package), reporting the issue to the distro maintainers may be more appropriate.
The "In-Reply-To" header is described in rfc2822. It is an explicit header in the RFC that is how you create threads.
Every mail client I've used correctly understands how to thread reply-chains using In-Reply-To.
The thing you're talking about, steam receipts grouping, is not a feature of email, but a specific feature of gmail's web view which is not mandated by any RFC and indeed is not explicit threading...
But there is a real way to thread which is defined in the RFC, and if you use a reasonable email client (aka not gmail), every mailing list's threading will work for you.
The code in question was: https://github.com/grpc/grpc-go/blob/b597a8e1d0ce3f63ef8a7b6...
That meant that deploying a service which drained in less than 30s would have a little mini-outage for that service until the in-process DNS cache expired, with of course no way to configure it.
Kuberesolver streams updates, and thus lets clients talk to new pods almost immediately.
I think things are a little better now, but based on my reading of https://github.com/grpc/grpc/issues/12295, it looks like the dns resolver still might not resolve new pod names quickly in some cases.