Title: How do I determine what deprecated features I am using?

Envoy version: Varies as we rollout between 1.10.0, 1.11.0, 1.11.1

Description:
We have envoy instances emitting the envoy.runtime.deprecated_feature_use metric but I am unable to figure out what features we are using that are deprecated.

The breaking change policy mentions the following:

during the first release cycle after a feature has been deprecated, use of that feature will cause a logged warning, and incrementing the runtime runtime.deprecated_feature_use stat.

However, I am unable to see these logs. These envoys are using the INFO log level.

How I tried to figure this out:

1. Compare the deprecation log with our config.
2. Run envoy locally with debug log level and attempt to use a deprecated feature.
3. View the logs of all envoys deployed for any mention of deprecated.

Questions:

1. At what log level can I expect to see the logged warning on use of a deprecated feature?
2. How do you expect people to go from runtime.deprecated_feature_use to the specific feature that is deprecated?

Relevant Links:

• https://www.envoyproxy.io/docs/envoy/latest/intro/deprecated.html
• https://github.com/envoyproxy/envoy/blob/master/docs/root/intro/deprecated.rst