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I believe you are misinterpreting the error.

Could not find address for mongo-2.mongo:27017: SocketException: Host not found (authoritative)"

The pod is created with an IP attached. Then it's registered into DNS:

Pod-0 has the IP 10.0.0.10 and now it's FQDN is Pod-0.servicename.namespace.svc.cluster.local

Pod-1 has the IP 10.0.0.11 and now it's FQDN is Pod-1.servicename.namespace.svc.cluster.local

Pod-2 has the IP 10.0.0.12 and now it's FQDN is Pod-2.servicename.namespace.svc.cluster.local

But DNS is a live service, IPs are dynamically assigned and can't be duplicated. So whenever it receives a request:

"Connect me with Pod-A.servicename.namespace.svc.cluster.local"

It tries to reach the registered IP and if the Pod is offline due to a rolling update, it will think the pod is unavailable and will return "Could not find the address (IP) for Pod-0.servicename" until the pod is online again or until the IP reservation expires and only then the DNS registry will be recycled.

The DNS is not discarting the DNS name registered, it's only answering it's currently offline.

You can either ignore the errors during the rolling or rethink your script and try using the internal js environment as mentioned in the comments for continuous monitoring of the mongo status.

EDIT:

• When Pods from a StatefulSet with N replicas are being deployed, they are created sequentially, in order from {0..N-1}.
• When Pods are being deleted, they are terminated in reverse order, from {N-1..0}.
• This is the expected/desired default behavior.
• So the error is expected, since the rollingUpdate makes the pod temporarily unavailable.