Question

A financial services company runs a fleet of 200 backend VMs (no external IPs) in a single subnet. These VMs make a very high volume of outbound API calls to a small number of external partner endpoints. Operations reports intermittent connection failures, and Cloud NAT logs show numerous 'OUT_OF_RESOURCES' drop entries for allocation, even though CPU and network throughput are well within limits. The team needs to resolve the failures without adding public IPs to the VMs. What is the most effective action?

Accepted Answer

Increase the minimum ports per VM instance allocation on the Cloud NAT gateway (and consider enabling dynamic port allocation) so more source ports are available for connections to the same destination.

Answer

Assign ephemeral external IP addresses to the backend VMs so they can bypass the NAT gateway for outbound traffic.

Answer

Lower the TCP established idle timeout to 30 seconds so ports are recycled, and leave the default 64 ports per VM unchanged.

Answer

Replace Cloud NAT with a Secure Web Proxy to handle all outbound partner API traffic and rely on its connection pooling.