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
- Public-facing SLB instances
A public-facing SLB instance distributes client requests over the Internet to backend servers according to configured forwarding rules.
When you create a public-facing 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.
- Internal SLB instances
Internal SLB instances can only be used inside Alibaba Cloud and can only forward requests from clients that can access the internal network of SLB.
For an internal SLB instance, you can select the network type:
- Classic network
If you choose classic network for an internal 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 internal 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.
- Classic network
Specification
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 is 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 number of new connections that 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.
- Max Connection
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. |