1. How is Server Load Balancer billed?

See Pay-As-You-Go.

2. Is the inbound traffic of SLB billed?

No. Only the outbound traffic of SLB is billed. For more information, see Network traffic flow.

3. Is the traffic generated by health check billed?

No. The traffic generated by the health check of SLB is not included in the billed traffic.

4. Will the billing of an ECS instance be affected after it is added to the backend server pool of SLB?

No. Regardless of the billing method used for the backend ECS instance, the billing method remains the same after you associate the instance with SLB. SLB and the backend ECS instance are billed separately based on usage.

5. Is attack traffic billed?

Integrating with Alibaba Cloud Security, SLB can defend against up to 5 Gbps DDoS attacks. From the time when the attack reaches the scrubbing or blackholing threshold to the time when the Alibaba Cloud Security starts scrubbing or blackholing, there may be a latency of several seconds. Therefore, the response to attack packets during this period will incur fees. Such an attack also consumes the bandwidth resources of SLB.

6. If all the backend ECS instances of an SLB instance are stopped, or all the backend ECS instances are removed, is the SLB billed?

Yes. Fees may be incurred and billable based on the following:

  • Billing by traffic

    In the case of billing by traffic, no traffic fee is generated when an instance is stopped, released, or not accessed.

    SLB is a traffic distribution control service in front of backend ECS instances and provides services through its service address. If all backend ECS instances are stopped, but the SLB instance is not stopped, inbound traffic can still reach the service address of the SLB instance. In this case, the SLB instance will respond if it discovers that there are no available backend ECS instances by performing health check.

    For Layer-4 SLB, only three-way handshake packets are returned. For Layer-7 SLB, a Tengine 503 error page is prompted because the service is provided by Tengine. If there are ongoing requests, SLB will respond continuously. Such response traffic is billed.

    This also applies to SLB instances with no ECS instances added. Therefore, we recommend that you stop the SLB instance if it is unnecessary in order to avoid extraneous costs.

  • Billing by bandwidth

    In the case of billing by bandwidth, fees are independent of instance status and traffic usage. You are charged if you activate the service. Billing ends only after the instance is released.