High-performance Classic Load Balancer (CLB) instances provide guaranteed performance. This topic provides answers to some frequently asked questions about high-performance CLB instances.

What is a high-performance CLB instance?

A high-performance CLB instance provides guaranteed 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 instances. You can view the instance type in the CLB console.
Notice Shared-resource CLB instances are no longer available for purchase.

The following table describes the differences between shared-resource CLB instances and high-performance CLB instances.

Feature Shared-resource CLB instance High-performance CLB instance
Resource allocation Shared resources Exclusive resources
Service uptime guaranteed by terms of service level agreement Not supported 99.95%
IPv6 ×
Server Name Indication (SNI) for multiple certificates ×
Blacklists and whitelists ×
Associating with elastic network interfaces (ENIs) ×
Adding 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) ×

You can move the pointer over the question mark that corresponds to the specification of a high-performance CLB instance to view the performance metrics, as shown in the following figure.

Performance metrics of high-performance CLB instances

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. When 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 are established per second. When the CPS value 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. When the QPS value 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 the region. You can go to the buy page of the CLB console to view the available specifications in each region.

Table 1. Specifications of high-performance CLB instances
Specification Maximum number of connections CPS QPS Purchase method
Small I (slb.s1.small) 5,000 3,000 1,000 Available for purchase from the official website of Alibaba Cloud.
Standard I (slb.s2.small) 50,000 5,000 5,000 Available for purchase from the official website of Alibaba Cloud.
Standard II (slb.s2.medium) 100,000 10,000 10,000 Available for purchase from the official website of Alibaba Cloud.
Higher I (slb.s3.small) 200,000 20,000 20,000 Available for purchase from the official website of Alibaba Cloud.
Higher II (slb.s3.medium) 500,000 50,000 30,000 Available for purchase from the official website of Alibaba Cloud.
Super I (slb.s3.large) 1,000,000 100,000 50,000 Available for purchase from the official website of Alibaba Cloud.
Note If you require a higher QPS, you can purchase Application Load Balancer (ALB) instances. For more information, see What is Application Load Balancer (ALB)?.

How are the fees for high-performance CLB instances calculated?

The fees for high-performance CLB instances are calculated by using the following formula:

Total fees for a CLB instance = Instance fee + Data transfer fee or bandwidth fee + Specification fee

The specification fee for a high-performance CLB instance is calculated based on the actual usage.

For example, you purchase a CLB instance of the Super I (slb.s3.large) specification, which supports at most 1,000,000 concurrent connections, 500,000 CPS, and 50,000 QPS. The following table describes the actual usage in each dimension.
Maximum number of connections CPS QPS
90000 4000 11000
  • The maximum number of concurrent connections processed by the CLB instance is 90,000, which is higher than the 50,000 limit defined in Standard I (slb.s2.small) and lower than the 100,000 limit defined in Standard II (slb.s2.medium). In this case, Standard II (slb.s2.medium) is used for the hour.
  • The maximum number of new connections processed by the CLB instance per second is 4,000, which is higher than the 3,000 limit defined in Small I (slb.s1.small) and lower than the 5,000 limit defined in Standard I (slb.s2.small). In this case, Standard I (slb.s2.small) is used for the hour.
  • The maximum number of requests processed by the CLB instance is 11,000, which is higher than the 10,000 limit defined in Standard II (slb.s2.medium) and lower than the 20,000 limit defined in Higher I (slb.s3.small). In this case, Higher I (slb.s3.small) is used for the hour.

    The QPS value is the highest among the preceding dimensions. Therefore, the specification fee for the hour is calculated based on the price of Higher I (slb.s3.small).

The hourly specification fee is calculated based on the preceding method. The following figure shows an example.Method for calculating the hourly specification fee-2

Therefore, the billing of high-performance CLB instances is flexible. The specification that you select when you purchase a CLB instance represents the upper performance limit of the CLB instance. For example, if you select Higher II (slb.s3.medium), the performance cannot be higher than Higher II (slb.s3.medium).

How do I choose among the specifications?

The specification fee is calculated based on actual usage. We recommend that you select the highest specification (slb.s3.large) available to ensure service availability at zero extra cost. However, if the capacity of Super I (slb.s3.large) significantly exceeds your business requirements, you can select a more appropriate specification, for example, Higher II (slb.s3.medium).

Can I change the specification of a high-performance CLB instance?

Yes, you can change the specification of a high-performance CLB instance in the console.

Note
  • 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.
  • Changing a shared-resource CLB instance to a high-performance CLB instance does not adversely affect your workloads, or change the IP address of the CLB instance.
    Note However, we recommend that you change 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 change the CLB instance.
  • The IP addresses of CLB instances are not affected when you change instance specifications.

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.

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 Higher I (slb.s3.small) specification. When the QPS value reaches 20,000, new connection requests are dropped by the CLB instance even if the number of concurrent connections has not reached 200,000.

Are shared-resource CLB instances still available for purchase?

No, shared-resource CLB instances are no longer available for purchase.

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.

The specification fee for an internal-facing CLB instance is calculated in the same way as the specification fee for an Internet-facing CLB instance. You are not charged instance fees or data transfer fees when you use internal-facing CLB instances.

What do I do if I need more high-performance CLB instances?

If the highest quota that you can apply for on the Quota Management page cannot meet your business requirements, you can apply for the slb_privilege_allow_more_guaranteed_performance_instances privilege. This privilege allows you to own more high-performance CLB instances but does not allow you to own more shared-resource CLB instances. For more information, see Quota management.

Why does the instance type remain unchanged after I upgrade a shared-resource CLB instance to a high-performance CLB instance?

If you change the metering method (pay-by-bandwidth or pay-by-data-transfer) when you upgrade a shared-resource CLB instance to a high-performance CLB instance, the new instance type and the new metering method take effect at 00:00:00 the next day.