The Alibaba Cloud provides both Layer-4 (TCP and UDP) and Layer-7 (HTTP and HTTPS) load balancing services.
Through health check on backend ECS instances, Server Load Balancer can automatically block abnormal ECS instances and distribute requests to them again when they become normal.
Server Load Balancer supports session persistence. You can set listening rules to forward the session request from a client to the same backend ECS instance during the session lifecycle.
Server Load Balancer supports the following scheduling algorithms:
Requests are distributed across the group of the backend ECS servers sequentially.
Weighted round robin (WRR)
You can set a weight for each backend server. Servers with higher weights receive more requests than those with less weights.
Weighted least connections (WLC)
In addition to the weight set to each backend ECS server, the number of connections to the client is also considered. The servers with a higher weight value will receive a larger percentage of live connections at any one time. If the weights are the same, the system directs network connections to the server with the least number of established connections.
Domain name/URL-based forwarding
For Layer-7 (HTTP and HTTPS) protocols, Server Load Balancer forwards traffic to different VServer groups based on the domain names or URLs.
To provide a more stable and reliable load balancing service, Alibaba Cloud Server Load Balancer has deployed multiple zones in most regions. When the primary zone is abnormal, the backup zone automatically takes over the load balancing service from the faulty zone.
You can set a whitelist to control which IP addresses can access the Server Load Balancer service.
Server Load Balancer supports application firewalls and HTTP Flood protection. Combined with Alibaba Cloud Security, the system can defend against DDoS attacks under 5 Gbps.
The Server Load Balancer service provides the Certificate Management function for the HTTPS protocol listening. With the Certificate Management service, you do not need to upload certificates to backend ECS instances. Deciphering is performed on Server Load Balancer in order to reduce the CPU overheads of backend ECS instances.
You can set the bandwidth peak for each listener based on the service that the application can provide.
You can choose to create a public or a private Server Load Balancer service. The system will assign a public IP address or a private IP address accordingly.
With the Monitor function, you can get the real-time status of your Server Load Balancer service.
You can manage Server Load Balancer instances through various methods, such as the Server Load Balancer console, Open API and SDK.