A Server Load Balancer (SLB) instance is a running entity of the SLB service. To use the SLB service, you must create an SLB instance and add listeners and backend servers to the instance.

Instance network types

Apsara Stack provides Internet-facing and internal-facing SLB instances. You can create Internet-facing SLB instances or internal-facing SLB instances based on your business requirements. If you create an Internet-facing SLB instance, a public IP address is allocated. If you create an internal-facing SLB instance, a private IP address is allocated.Instance network types
  • Internet-facing SLB instances

    An Internet-facing SLB instance distributes client requests over the Internet to backend servers based on configured forwarding rules. An internal-facing SLB instance in a virtual private cloud (VPC) can process requests sent over the Internet only when the instance is associated with an elastic IP address (EIP). The following table provides more detailed information.

    Type Feature
    Internet-facing SLB instances

    After you create an Internet-facing SLB instance, the system allocates a public IP address to the instance. You can bind a domain name to the public IP address to provide external services.

    • The public IP address is allocated to the SLB instance and cannot be unbound from the instance.
    • Internet-facing SLB instances support only pay-by-data-transfer and pay-by-bandwidth billing methods.
    Internal-facing SLB instances that are associated with EIPs

    An internal-facing SLB instance that is associated with an EIP can process requests sent over the Internet.

    • A public IP address is allocated to the EIP. You can associate the EIP with the SLB instance and disassociate the EIP from the SLB instance based on your requirements.
    • An EIP that is associated with an EIP bandwidth plan supports the 95th percentile bandwidth billing method.
  • Internal-facing SLB instances

    Internal-facing SLB instances can be used only inside Apsara Stack and can forward only requests from clients that can access SLB instances over the internal network.

    You can select one of the following network types for an internal-facing SLB instance:

    • Classic network

      If you choose classic network for an internal-facing SLB instance, the IP address of the SLB instance is allocated and maintained by Apsara Stack. This instance can be accessed only by Elastic Compute Service (ECS) instances in the classic network.

    • VPC

      If you choose VPC for an internal-facing SLB instance, the IP address of the SLB instance is allocated from the CIDR block of the vSwitch that is attached to the VPC. This SLB instance can be accessed only by ECS instances in the VPC.

Instance types and specifications

Alibaba Cloud provides shared-performance SLB instances and guaranteed-performance SLB instances. Guaranteed-performance SLB instances provide reliable performance metrics.

  • Shared-performance SLB instances

    All shared-performance SLB instances share SLB resources. This indicates that the instance performance cannot be guaranteed.

  • Guaranteed-performance SLB instances

    The following content describes three key metrics of guaranteed-performance SLB instances:

    • Max Connection

      The maximum number of concurrent connections that an SLB 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.

Apsara Stack provides four types of guaranteed-performance SLB instances.

For more information, see FAQ about high-performance SLB instances.

Type Specification Max connection 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 Apsara Stack.
Type 2 Standard I (slb.s2.small) 50,000 5,000 5,000 Available for purchase from the official website of Apsara Stack.
Type 3 Standard II (slb.s2.medium) 100,000 10,000 10,000 Available for purchase from the official website of Apsara Stack.
Type 4 Higher I (slb.s3.small) 200,000 20,000 20,000 Available for purchase from the official website of Apsara Stack.

The following table describes the differences between shared-performance SLB instances and guaranteed-performance SLB instances.

Feature Shared-performance SLB instance Guaranteed-performance SLB instance
Resource allocation Shared resources Exclusive resources
Service level agreement for guaranteed availability Not supported 99.95%
IPv6 ×
Server Name Indication (SNI) certificates ×
Support for blacklists and whitelists ×
Elastic network interface (ENI) mounting ×
Assignment of secondary IP addresses to ENIs that are bound to ECS instances ×
HTTP-to-HTTPS redirection ×
Consistent hashing ×
TLS security policies ×
HTTP2 ×
Websocket(S) ×