Question

After promoting a standby web server to a new public IP, an operations engineer updates the application's DNS A record and confirms the change is correct on the authoritative name server. However, roughly 40% of users continue to reach the old, now-unreachable IP address for over an hour, while the rest connect successfully. Using a structured troubleshooting methodology, what is the MOST likely root cause?

Accepted Answer

The DNS record's TTL was set to a high value, so many resolvers and clients are still serving the cached old IP until it expires.

Answer

The authoritative name server is returning both the old and new IP addresses in a round-robin configuration.

Answer

The new web server's security group is blocking inbound traffic from 40% of the client source IP ranges.

Answer

The load balancer health check is intermittently marking the new server unhealthy, removing it from rotation.