The default /etc/resolve.conf configuration for ndots is 1 for most Linux systems, however in a Kubernetes environment the DNS for Services and Pods defaults this value to 5 (see "Kubernetes pods /etc/resolv.conf ndots:5 option and why it may negatively affect your application performances").

Service discovery in k8s can span the cluster namespace, cluster scope, private DNS (Azure in particular uses this), and so on before trying a fully terminated (non-search) domain. For MongoDB Atlas' SRV records, if the DNS query fails to search all the search domains before resolving the TXT record the authSource=admin URI component will not be appended to the connection string and the MongoClient connection will fail due to an authentication issue.

This issue manifested in PYTHON-3536 but could likely affect all drivers.