Question

A company runs a hub-and-spoke topology using a Transit Gateway with multiple VPC attachments across three Availability Zones. Application teams report intermittent high latency for east-west traffic between two spoke VPCs, but only for flows that traverse different AZs. The network team must confirm whether traffic is being hairpinned across AZs at the Transit Gateway before opening a support case. Which action provides the most direct evidence of the cross-AZ traffic behavior?

Accepted Answer

Enable Transit Gateway Flow Logs and analyze the source/destination AZ fields (az-id) to determine whether ingress and egress occur in different Availability Zones for the affected flows

Answer

Enable VPC Flow Logs on both spoke VPC ENIs and inspect the packet byte counts to infer additional inter-AZ hops

Answer

Run Reachability Analyzer between the two spoke instances to measure the round-trip latency across the Transit Gateway

Answer

Use CloudWatch metrics for BytesIn and BytesOut on the Transit Gateway to identify which AZ is generating cross-zone charges