Alibaba Cloud Server Load Balancer (SLB) is a service that distributes and controls network traffic. SLB includes Classic Load Balancer (CLB) and Application Load Balancer (ALB), offering high availability, scalability, cost-effectiveness, security, and support for high concurrency. You can bind an SLB instance to your Enterprise Distributed Application Service (EDAS) application. The SLB instance acts as a traffic ingress and distributes traffic to different application instances based on forwarding rules.
Use SLB to access EDAS applications on ECS
EDAS supports applications hosted on Alibaba Cloud Elastic Compute Service (ECS) clusters and hybrid cloud ECS clusters. You can use the EDAS ECS environment to host applications that use popular Java microservice frameworks, such as Spring Cloud and Dubbo, or the High-speed Service Framework (HSF). After an application is deployed on the EDAS platform, its multiple instances must work together to provide services. This requires a unified traffic ingress and a traffic distribution service to forward access requests to different backend application instances based on forwarding rules.
An EDAS application uses an SLB instance as the traffic ingress. The application instances act as the backend servers for the SLB instance. The SLB instance forwards traffic to the application instances based on forwarding rules. The following figure shows how an EDAS application is bound to an SLB instance:
You can combine a multi-instance application with SLB to ensure high availability, reduce the load on individual servers, and distribute traffic. SLB lets you configure scheduling algorithms for backend servers, such as round-robin and weighted round-robin. If you enable session persistence, requests from the same client are forwarded to the same backend application server, which improves access performance.
EDAS supports adding load balancing using ALB and CLB. If you use complex routing rules, use ALB.
- ALB: Application Load Balancer (ALB) provides powerful application-layer processing capabilities and rich, advanced routing features. It focuses on HTTP, HTTPS, and QUIC application-layer protocols and serves as the official cloud-native Ingress gateway of Alibaba Cloud. For more information, see What is Application Load Balancer (ALB).
- CLB: CLB uses a virtual service address to combine multiple ECS instances in the same region into a high-performance and high-availability backend server pool. It then distributes requests from clients to the ECS instances in the pool based on forwarding rules. By default, CLB checks the health of the ECS instances in the server pool and automatically isolates unhealthy instances, eliminating single points of failure and improving the overall service capability of your application. CLB also provides mitigation capabilities against DDoS attacks, enhancing the security of your application services. For more information, see What is Classic Load Balancer (CLB).
How to choose an SLB usage method for your application
When using load balancing for an application, you can choose from the following methods based on your scenario.
| Scenario | References |
| Dedicated SLB instance for a single application | Configure a dedicated SLB instance for an application |
| Use URLs to distribute traffic among different instance groups of a single application | Use URLs to distribute traffic to instance groups of an application |
| Use ports to distribute traffic when multiple applications share an SLB instance | Use ports to distribute traffic (shared SLB instance) |
| Use a domain name or URL to distribute traffic when multiple applications share an SLB instance | Use a domain name or URL to distribute traffic (shared SLB instance) |