A Server Load Balancer (SLB) instance is a virtual machine in which the SLB service runs. To use the SLB service, you must create an SLB instance first, and then add listeners and backend servers to the SLB instance.

Instance network type

Alibaba Cloud provides Internet and intranet SLB services. If you create an Internet SLB instance, a public IP address is allocated to it. If you create an intranet SLB instance, a private IP address is allocated.
  • Internet SLB instances

    An Internet SLB instance distributes client requests over the Internet to backend servers according to configured forwarding rules.

    When you create an Internet SLB instance, the system allocates a public IP address to the instance. You can resolve a domain name to the public IP address to provide public services.

  • Intranet SLB instances

    Intranet SLB instances can only be used inside Alibaba Cloud and can only forward requests from clients that can access the intranet of SLB.

    For an intranet SLB instance, you can select the network type:

    • Classic network

      If you choose classic network for an intranet SLB instance, the IP address of the SLB instance is allocated and maintained by Alibaba Cloud. The instance can only be accessed by classic-network ECS instances.

    • VPC network

      If you choose VPC network for an intranet SLB instance, the IP address of the SLB instance is allocated from the CIDR block of the VSwitch that the instance belongs to. An SLB instance of the VPC-type network can only be accessed by ECS instances in the same VPC.

Instance specifications

SLB provides shared-performance instances and guaranteed-performance instances.

  • Shared-performance instances

    All shared-performance instances share SLB resources, which means their performance cannot be guaranteed.

  • Guaranteed-performance instances

    The performance of guaranteed-performance instances are set according to their selected specifications. The following are three key performance indicators of guaranteed-performance instances:

    • Max Connection

      The maximum number of connections to an SLB instance. When the number of connections reaches the limit of the specification, new connection requests are dropped.

    • Connection Per Second (CPS)

      The rate at which new connections are established per second. When the CPS reaches the limit of the specification, new connection requests are dropped.

    • Queries Per Second (QPS)

      The number of HTTP/HTTPS requests that can be processed per second. This metric is available only for Layer-7 SLB listeners. When the QPS reaches the limit of the specification, new connection requests are dropped.

Currently, six specifications are available for guaranteed-performance instances. For more information, see Guaranteed-performance instance FAQ.

Type Specification Max Connection CPS QPS Purchase method
Specification 1 Small I (slb.s1.small) 5,000 3,000 1,000 Available for purchase from the official website of Alibaba Cloud.
Specification 2 Standard I (slb.s2.small) 50,000 5,000 5,000 Available for purchase from the official website of Alibaba Cloud.
Specification 3 Standard II (slb.s2.medium) 100,000 10,000 10,000 Available for purchase from the official website of Alibaba Cloud.
Specification 4 Higher I (slb.s3.small) 200,000 20,000 20,000 Available for purchase from the official website of Alibaba Cloud.
Specification 5 Higher II (slb.s3.medium) 500,000 50,000 30,000 Available for purchase from the official website of Alibaba Cloud.
Specification 6 Super I (slb.s3.large) 1,000,000 100,000 50,000 Available for purchase from the official website of Alibaba Cloud.
Specification 7 Super II (slb. s3.xlarge) 2,000,000 200,000 100,000 Contact your account manager.
Specification 8 Super III (slb. s3.xxlarge) 5,000,000 500,000 100,000 Contact your account manager.