Whether you incur traffic fees depends on the bandwidth billing method of your Server Load Balancer (SLB) instance:
Fixed bandwidth: No additional traffic fees. The traffic fee is already included in the SLB instance purchase price.
Pay-as-you-go bandwidth: Yes. Standard SLB traffic billing policies apply, and stress testing traffic counts toward your bill.
Avoid traffic fees by using private IP addresses
To avoid Internet traffic charges during stress testing, use one of the following addresses in your test script instead of the SLB public IP address:
The private IP address of the SLB instance
The internal IP address of the Elastic Compute Service (ECS) instance associated with the SLB instance
Traffic sent to these addresses routes through the internal network and bypasses public bandwidth billing.