Rather than setting the dns_refresh_rate for a cluster, it would be nice to be able to just respect the TTL returned in the DNS response. I was wondering is this intentionally not supported, or just has not been needed yet? If not, would there be interest in adding this feature?

If there is nothing blocking such a change, please let me know and I can consider working on this feature.

Background: We get a lot of reports of high DNS requests from Envoy from Istio users. The cause of this is clear - we use the default dns_refresh_rate of 5s, so each STRICT_DNS cluster is sending a lot of DNS requests.

Our proposed mitigation is to change the default to 5min, to match a typical TTL. However, this isn't a perfect solution, as some services we would actually want a lower refresh rate, and would prefer to not need to set for each service.

More background: istio/istio#13710