This topic provides answers to frequently asked questions about Classic Load Balancer (CLB) instances.
Can I change the specification of a high-performance CLB instance?
Can I change the primary and secondary zones of a CLB instance after creation?
How do I choose a pay-as-you-go instance?
Starting from June 1, 2025 at 00:00:00 (UTC+8), CLB pay-by-specification instances will no longer be available for purchase.
CLB instances use pay-by-LCU by default. Instance performance automatically scales based on usage, and you do not need to specify a specification. You are charged for LCUs based on actual usage per hour. For performance limits, see Instance performance limits. For billing methods, see Instance billing methods.
Why is a high-performance CLB instance unable to reach the performance limit defined in the specification?
This issue can be explained by the cask theory. High-performance CLB instances do not guarantee that the three metrics (including bandwidth) can reach the upper limits of a specification at the same time. If one of the metrics reaches the upper limit, the instance performance is limited.
For example, if a user selects a Large I (slb.s3.small) instance, when the instance's QPS reaches 20,000 but the number of concurrent connections has not reached 200,000, the maximum number of connections may never reach the specification limit because new connection requests will be dropped when QPS reaches its limit.
Can I change the specification of a high-performance CLB instance?
Yes, you can.
You can change the specification of a high-performance CLB instance in the console. For more information, see Modify the configurations of pay-as-you-go CLB instances.
Starting from June 1, 2025 at 00:00:00 (UTC+8), CLB pay-by-specification instances will no longer be available for purchase. Pay-by-LCU instances will no longer support changing to pay-by-specification. For more information, see Discontinuation Notice for Classic Load Balancer pay-by-specification instances.
You can change only shared-resource CLB instances to high-performance ones. You cannot change high-performance CLB instances to shared-resource ones.
Changing a shared-resource CLB instance to a high-performance CLB instance does not affect your workloads or change the IP address of the CLB instance.
The IP addresses of CLB instances remain unchanged when you change instance specifications.
We recommend that you change a shared-resource CLB instance to a high-performance CLB instance during off-peak hours, or implement load balancing between instances through DNS before making the change.
Why does the instance specification remain unchanged after I change the specification of a high-performance CLB instance?
If you change the metering method (pay-by-bandwidth or pay-by-data-transfer) when you change the specification of a high-performance CLB instance, the new instance specification and the new metering method take effect at 00:00:00 the next day.
Can I change the primary and secondary zones of a CLB instance after creation?
No, you cannot.
After a CLB instance is created, you cannot modify the primary zone. The system automatically selects the most appropriate secondary zone based on the actual situation in each region, and you do not need to configure it manually.
We recommend that you use Application Load Balancer (ALB) and Network Load Balancer (NLB), which support multi-zone policies. For more information, see Introduction to Server Load Balancer product family, What is Application Load Balancer?, and What is Network Load Balancer?.