This topic provides answers to some frequently asked questions about Classic Load Balancer (CLB).
What are the billing rules of high-performance CLB instances?
Am I charged a specification fee for an internal-facing CLB instance?
How do I choose among the specifications for high-performance CLB instances?
Can I change the specification of a high-performance CLB instance?
Can I associate an EIP with the static public IP address of an Internet-facing CLB instance?
Can I change the primary and secondary zones of a CLB instance?
What is a high-performance CLB instance?
High-performance CLB instances provide reliable performance. Shared-resource CLB instances share resources with each other and their performance is not guaranteed.
Before Alibaba Cloud launched high-performance CLB instances, all CLB instances were shared-resource CLB instances. You can view the instance type in the CLB console.
Shared-resource instances are no longer available for purchase.
The following section describes the metrics of high-performance CLB instances:
Maximum number of connections
The maximum number of concurrent connections that a CLB instance supports. If the number of existing concurrent connections reaches the upper limit, new connection requests are dropped.
Connections per second (CPS)
The number of new connections that can be established per second. If CPS reaches the upper limit, new connection requests are dropped.
Queries per second (QPS)
The number of HTTP or HTTPS queries (requests) that can be processed per second. This metric is specific to Layer 7 listeners. If QPS reaches the upper limit, new connection requests are dropped.
The following table describes the specifications of high-performance CLB instances provided by Alibaba Cloud. The available specifications vary based on regions. You can go to the buy page of CLB instances to view the available specifications in each region.
| Specification | Maximum number of connections | CPS | QPS |
| Small I (slb.s1.small) | 5,000 | 3,000 | 1,000 |
| Medium I (slb.s2.small) | 50,000 | 5,000 | 5,000 |
| Medium II (slb.s2.medium) | 100,000 | 10,000 | 10,000 |
| Large I (slb.s3.small) | 200,000 | 20,000 | 20,000 |
| Large II (slb.s3.medium) | 500,000 | 50,000 | 30,000 |
| Super Large I (slb.s3.large) | 1,000,000 | 100,000 | 50,000 |
The maximum capacity of a pay-by-LCU CLB instance is the same as a Super Large I (slb.s3.large) CLB instance.
If you require a larger number of connections at Layer 4, use Network Load Balancer (NLB). If you require more queries per second at Layer 7, use Application Load Balancer (ALB).
For more information about NLB, see What is NLB?
For more information about ALB, see What is ALB?
What are the billing rules of high-performance CLB instances?
For more information about billing of pay-as-you-go CLB instances, see Pay-as-you-go.
Pay-by-specification
Total fees for an Internet-facing high-performance CLB instance = Instance fee + Data transfer fee or bandwidth fee + Specification fee
You are charged a specification fee on an hourly basis based on the specification that you select. For example, if you select the Super Large I (slb.s3.large) specification for a CLB instance, but the performance metrics of an hour are the same as the performance metrics of a Large I (slb.s3.small) CLB instance, you are still charged a specification fee based on the Super Large I (slb.s3.large) specification for the hour.
Pay-by-LCU
Total fees for an Internet-facing high-performance CLB instance = Instance fee + Data transfer fee + Loadbalancer Capacity Unit (LCU) fee
If you use the pay-by-LCU metering method, you do not need to specify a specification for a CLB instance. The CLB instance automatically adds or releases resources on demand. You are charged an LCU fee based on the actual resources that are consumed per hour.
Am I charged a specification fee for an internal-facing CLB instance?
You are not charged a specification fee for a shared-resource internal-facing CLB instance. You are charged a specification fee for a high-performance internal-facing CLB instance.
You are charged specification fees for internal-facing CLB instances in the same way you are charged for Internet-facing CLB instances. You are not charged instance fees or data transfer fees for internal-facing CLB instances.
How do I choose among the specifications for high-performance CLB instances?
If your workloads expect only minor fluctuations, we recommend that you select pay-by-specification. You are charged a specification fee on an hourly basis based on the specification that you select.
If your workloads expect periodic or large fluctuations, we recommend that you select pay-by-LCU. Pay-by-LCU CLB instances can automatically scale resources on demand. In addition, you do not need to specify a specification. You are charged for consumed LCUs on an hourly basis.
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 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, you purchase a high-performance CLB instance of the slb.s3.small specification. When QPS reaches 20,000, new connection requests are dropped by the CLB instance even if the number of concurrent connections has not reached 200,000.
Can I change the specification of a high-performance CLB instance?
Yes, you can upgrade a shared-resource CLB instance to a high-performance CLB instance.
you can change the specification of a high-performance CLB instance in the CLB console. For more information, see Modify the configurations of pay-as-you-go CLB instances.
- You can change only shared-resource CLB instances to high-performance CLB instances. You cannot change high-performance CLB instances to shared-resource CLB instances.
When you upgrade a shared-resource CLB instance to a high-performance CLB instance, your services are not affected and the IP address of the CLB instance remains unchanged.
We recommend that you upgrade a shared-resource CLB instance to a high-performance CLB instance during off-peak hours. You can also configure DNS resolution to replace your current load balancing service before you upgrade the CLB instance.
The IP addresses of CLB instances remain unchanged when you change instance specifications.
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.
What are the features of shared-resource CLB instances?
Question | Answer |
Can I purchase shared-resource CLB instances? | No, shared-resource CLB instances are no longer available for purchase. |
Do shared-resource CLB instances provide different specifications? | The performance of shared-resource CLB instances is not guaranteed. Therefore, you cannot specify the specification of a shared-resource CLB instance. |
Am I charged specification fees for existing shared-resource CLB instances? | No, you are not charged specification fees for existing shared-resource CLB instances. You are charged specification fees only if you upgrade the shared-resource CLB instances to high-performance CLB instances. After the free trial for high-performance CLB instances ends, you are charged specification fees if you use high-performance CLB instances. |
Can I upgrade a shared-resource CLB instance to a high-performance CLB instance? | Yes, you can upgrade a shared-resource CLB instance to a high-performance CLB instance.
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The following table describes the differences between shared-resource CLB instances and high-performance CLB instances.
Item | Shared-resource CLB instance | High-performance CLB instance |
Resource allocation | Shared resources | Exclusive resources |
Service uptime guaranteed by terms of service level agreement (SLA) | Not supported | 99.95% |
IPv6 | × | ✔ |
Server Name Indication (SNI) | × | ✔ |
Blacklists and whitelists | × | ✔ |
Association with elastic network interfaces (ENIs) | × | ✔ |
Add secondary IP addresses of ENIs that are associated with Elastic Compute Service (ECS) instances | × | ✔ |
HTTP-to-HTTPS redirection | × | ✔ |
Consistent hashing | × | ✔ |
TLS security policies | × | ✔ |
HTTP2 | × | ✔ |
Websocket(S) | × | ✔ |
Can I associate an EIP with the static public IP address of an Internet-facing CLB instance?
No, you cannot directly associate an EIP with the static public IP address of an Internet-facing CLB instance.
However, you can associate an EIP with a CLB instance by using one of the following methods:
Purchase an internal-facing CLB instance and associate an EIP with the CLB instance. For more information, see Create and manage a CLB instance and Associate and manage an EIP.
Purchase an Internet-facing ALB instance. By default, an EIP is associated with the Internet-facing ALB instance to enable Internet access. For more information, see Create an ALB instance.
Purchase an Internet-facing NLB instance. By default, an EIP is associated with the Internet-facing NLB instance to enable Internet access. For more information, see Create and manage an NLB instance.
Can I change the primary and secondary zones of a CLB instance?
No, you cannot change the primary and secondary zones of a CLB instance.
You can purchase a CLB instance and specify a different primary or secondary zone for the CLB instance.
ALB and NLB support more flexible zone policies. We recommend that you use ALB and NLB. For more information, see What is SLB?, What is ALB?, and What is NLB?