Introduce a time buffer between targets refresh and lameduck invalidation. (#504)
Introduce a time buffer between targets refresh and lameduck invalidation. (#504)

This is to take care of the following race between targets refresh and lameduck creation:

Let's say targets are refreshed few seconds after lameduck, and are deleted few more seconds after that. If there is no min lameduck duration, we'll end up ignoring lameduck in this case as refresh timestamp will be after lameduck timestamp. With min lameduck duration, targets will need to be refreshed some time (5m) after being lameducked for lameduck to be ignored.

PiperOrigin-RevId: 342204018
cloudprober/cloudprober,cloudprober/cloudprober,cloudprober/cloudprober,google/cloudprober,google/cloudprober