How DNS in Message Processor Add and Reomve IPs ?

Google Cloud Apigee
,
1

I see in this documentation a problem called Connection errors due to incorrect DNS resolution

https://docs.apigee.com/api-platform/troubleshoot/runtime/503-service-unavailable#connectionerrorsdns

There is IPs added and deleted I just want to know ,

Where these IPs come from?

Why some of them are being deleted ?

Any Help ?