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. In comparison, shared-resource CLB instances share resources with each other, which means that performance cannot be guaranteed.

Before Alibaba Cloud released high-performance CLB instances, all instances were shared-resource instances. You can view the instance type in the CLB console.
Notice Shared-resource CLB instances are no longer available.

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 ×
Support for Server Name Indication (SNI) 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 ×
Support for 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 for high-performance CLB instances

The following section lists three key metrics for high-performance CLB instances:

  • Max Connection

    The maximum number of concurrent connections that a CLB instance supports. When the number of concurrent connections reaches the specified 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 specified 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 specified limit, new connection requests are dropped.

The following table lists the specifications of high-performance instances provided by Alibaba Cloud. The specifications available for purchase vary by region. You can go to the buy page of the CLB console to view the specifications available for purchase in your region.

Instance type Specification Maximum number of connections CPS QPS Purchase method
Type 1 Small I (slb.s1.small) 5,000 3,000 1,000 Available for purchase from the official website of Alibaba Cloud.
Type 2 Standard I (slb.s2.small) 50,000 5,000 5,000 Available for purchase from the official website of Alibaba Cloud.
Type 3 Standard II (slb.s2.medium) 100,000 10,000 10,000 Available for purchase from the official website of Alibaba Cloud.
Type 4 Higher I (slb.s3.small) 200,000 20,000 20,000 Available for purchase from the official website of Alibaba Cloud.
Type 5 Higher II (slb.s3.medium) 500,000 50,000 30,000 Available for purchase from the official website of Alibaba Cloud.
Type 6 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 specification, you can purchase Application Load Balancer (ALB) instances. For more information, see What is Application Load Balancer (ALB)?.

How are high-performance CLB instances billed?

High-performance CLB instances are billed based on the following formula:

Total fee (per instance) = Instance fee + Data transfer fee or bandwidth fee + Specification fee

The specification fee of a high-performance CLB instance is charged based on the actual usage no matter which specification you choose.

Assume that you purchase a CLB instance of the Super I (slb.s3.large) specification (Max Connection: 1,000,000; CPS: 500,000; QPS: 50,000). The following table lists the highest metric values of your CLB instance within an hour.
Max Connection CPS QPS
90000 4000 11000
  • The actual Max Connection value of 90,000 is between the limit of 50,000 defined in Standard I (slb.s2.small) and the limit of 100,000 defined in Standard II (slb.s2.medium). Therefore, the specification based on the Max Connection metric for this hour is Standard II (slb.s2.medium).
  • The actual CPS value of 4,000 is between the limit of 3,000 defined in Small I (slb.s1.small) and the limit of 5,000 defined in Standard I (slb.s2.small). Therefore, the specification based on the CPS metric for this hour is Standard I (slb.s2.small).
  • The actual QPS value of 11,000 lies between the limit of 10,000 defined in Standard II (slb.s2.medium) and the limit of 20,000 defined in Higher I (slb.s3.small). Therefore, the specification based on the QPS metric for this hour is Higher I (slb.s3.small).

    The QPS metric uses the highest specification (slb.s3.small) among three metrics. Therefore, the instance is charged based on the Higher I (slb.s3.small) specification for this hour.

The hourly specification fee is charged based on the preceding method. The following figure shows an example.Method to calculate the hourly specification fee-2

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

What is the optimal specification for a high-performance CLB instance?

The specification fee is charged based on your actual usage. We recommend that you select the highest specification (slb.s3.large) available to ensure service flexibility at no extra cost. However, if the capacity of Super I (slb.s3.large) significantly exceeds your business demand, you can select a more appropriate specification, such as 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 negatively affect your workloads, or change the IP address of the CLB instance.

    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.

Are specification fees charged by existing shared-resource CLB instances?

No.

Specification fees are not charged by existing shared-resource instances unless you change them to high-performance CLB instances. You can change a shared-resource CLB instance to a high-performance CLB instance by changing the specification. When you change a shared-resource CLB instance to a high-performance CLB instance, a specification fee is charged.

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. The instance performance is limited if one of the metrics reaches the upper limit.

Assume that you have purchased a high-performance CLB instance of the Higher I (slb.s3.small) specification. When the QPS of the instance reaches 20,000 but the number of maximum connections does not reach 200,000, new connection requests are dropped because the QPS limit is reached.

Are shared-resource CLB instances still available for purchase?

No.

Is a specification fee charged by an internal-facing CLB instance?

If the internal-facing CLB instance that you use is a shared-resource CLB instance, no specification fee is charged. If the internal-facing CLB instance is a high-performance CLB instance, a specification fee is charged.

The specification fees for internal-facing CLB instances are charged in the same way as Internet-facing CLB instances. No instance fees or data transfer fees are charged by internal-facing CLB instances.

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

If you need more high-performance CLB instances but the number of the instances has reached the quota, you can apply for the slb_privilege_allow_more_guaranteed_performance_instances privilege for a quota increase. 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 Manage quotas.