Classic Load Balancer (CLB) instances receive requests from clients and forward requests to backend servers. To use the load balancing service, you must create a CLB instance and add listeners and backend servers to the instance.
Alibaba Cloud provides Internet-facing and internal-facing CLB instances.
Internet-facing CLB instances
When you create an Internet-facing CLB instance, the system automatically assigns a public address to the CLB instance. You can associate your domain name with the public IP address. CLB instances receive requests from clients over the Internet and forward requests to backend servers based on the forwarding rules that you specify for listeners.
- The system assigns a public IP address to the CLB instance. You cannot disassociate the public IP address from the CLB instance.
- When the subscription billing method is used, only the pay-by-bandwidth metering method is supported. When the pay-as-you-go billing method is used, the pay-by-bandwidth and pay-by-data-transfer metering methods are supported.
Internal-facing CLB instances
Internal-facing CLB instances provide services over private networks. Internal-facing CLB instances receive requests from internal networks and forward requests to backend servers based on listener rules.
- An internal-facing CLB instance associated with an EIP can provide services over the Internet. You can disassociate the EIP from the CLB instance as needed.
- An EIP that is associated with an EIP bandwidth plan supports the pay-by-95th-percentile-bandwidth billing method in addition to the subscription and pay-as-you-go billing methods.
- Subscription internal-facing CLB instances support the following network types: classic
network and virtual private cloud (VPC).
If an internal-facing CLB instance is deployed in a VPC, the IP address of the CLB instance is allocated from the CIDR block of the vSwitch that is attached to the VPC. The internal-facing CLB instance can be accessed by only Elastic Compute Service (ECS) instances in the same VPC.
- Classic network
If the internal-facing CLB instance is deployed in a classic network, the private IP address of the CLB instance is allocated and managed by Alibaba Cloud. The internal-facing CLB instance can be accessed by only ECS instances in classic networks.Notice Internal-facing CLB instances of the classic network type are no longer available.
- Pay-as-you-go internal-facing CLB instances support only the VPC network type.
Internal-facing CLB instances support PrivateLink. Internal-facing CLB instances can receive requests from other VPCs through PrivateLink connections and distribute the requests to backend servers based on listener rules. For more information, see What is PrivateLink?.
Instance types and specifications
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.
|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.|
For more information, see FAQ about high-performance CLB instances.
Shared-resource CLB instance
The following table describes the differences between shared-resource and high-performance CLB instances.
|Feature||High-performance CLB instance||Shared-resource CLB instance|
|Resource allocation||Exclusive resources||Shared resources|
|Service uptime guaranteed by the service-level agreement (SLA)||99.95%||Not supported|
|Server Name Indication (SNI)||√||-|
|Blacklists and whitelists||√||-|
|Elastic network interface (ENI) mounting||√||-|
|Assigning secondary IP addresses to ENIs that are associated with ECS instances||√||-|
|TLS security policies||√||-|
|WebSocket or WebSocket Secure||√||-|