[cloud] Ensure absence of public_dns_name doesn't halt ec2 module (#31476)

lib/ansible/modules/cloud/amazon/ec2.py

@@ -1618,7 +1618,8 @@ def warn_if_public_ip_assignment_changed(module, instance):
     assign_public_ip = module.params.get('assign_public_ip')
 
     # Check that public ip assignment is the same and warn if not
-    if (assign_public_ip or instance.public_dns_name) and (not instance.public_dns_name or not assign_public_ip):
+    public_dns_name = getattr(instance, 'public_dns_name', None)
+    if (assign_public_ip or public_dns_name) and (not public_dns_name or not assign_public_ip):
         module.warn("Unable to modify public ip assignment to {0} for instance {1}. "
                     "Whether or not to assign a public IP is determined during instance creation.".format(assign_public_ip, instance.id))