What is Load Balancer?

A load balancer distributes traffic flows of a virtual IP address to backend servers. It automatically inspects the availability of backend servers and isolates unavailable servers during traffic distribution. This way, the load balancer improves the availability and service capability of your business.

The Cloud provides the following two types of load balancing services:
  • Shared-performance load balancing: uses a VPC vRouter to provide load balancing services. Traffic is distributed to backend servers by the VPC vRouter. If the VPC vRouter is providing multiple services, the load balancing service shares the performance of the VPC vRouter with other services.
  • Dedicated-performance load balancing: uses a load balancer instance to provide load balancing services. Traffic is distributed to backend servers by the load balancer instance. A load balancer instance is a custom VM instance dedicated to providing load balancing services.

Concepts

  • Frontend network: A frontend network is a type of network that is associated with a load balancer. Requests from the network are distributed by the load balancer to backend servers based on a specified policy.
    • Shared-performance load balancer: You can specify a public network or VPC network as a frontend network.
    • Dedicated-performance load balancer: You can specify a public network, flat network, or VPC network as a frontend network.
  • Backend network:A backend network is a type of network that is associated with a load balancer. Requests from frontend networks are distributed by the load balancer to servers in the backend network.
    • Shared-Performance Load Balancer:
      • If you specify a public network as the frontend network, you can specify any one of the VPC networks of the VPC vRouter to which the public network is attached as the backend network.
      • If you specify a VPC network as the frontend network, you can specify any one of the VPC networks of the VPC vRouter to which the VPC network is attached as the backend network.
    • Dedicated-Performance Load Balancer:
      • If you specify a public network as the frontend network, you can specify a flat network or any one of the VPC networks of the VPC vRouter to which the public network is attached as the backend network.
      • If you specify a flat network as the frontend network, you must specify the same network as the backend network.
      • If you specify a VPC network of a VPC vRouter as the frontend network, you must specify the same network as the backend network. If you need to associate the load balancer with more backend networks, you can attach more NICs to the load balancer instance. Note that the backend networks that you associate are among the other VPC networks of the VPC vRouter.
  • Load balancer instance: A load balancer instance is a custom VM instance used to provide load balancing services.
    • The network where the default NIC of a load balancer instance resides is the frontend network of the load balancer instance. The default NIC cannot be detached from a load balancer instance.
    • The networks of the NICs of a load balancer instance, except the default NIC, are the backend networks of the load balancer.
  • LB image:
    • An LB image is a custom image. You can download the image from the Cloud official website and add the image to the platform.
  • Load balancer instance: A load balancer (LB) instance offering defines the CPU, memory, image, and management network configuration settings used to create LB instances. LB instances provide load balancing services for the public network, flat network, and VPC network.
  • Listener: A listener monitors the frontend requests of a load balancer and distributes the requests to a backend server based on the specified policy. In addition, the listener performs health checks on backend servers.
    • Listeners support the TCP, HTTP, HTTPS, and UDP protocols.
    • A load balancer can be associated with multiple listeners while a listener can be associated with only one load balancer.
    • If the listener uses the weighted round-robin load-balancing algorithm, you can set the weight value for each individual backend server on the backend server group details page.
  • Forwarding rule: A forwarding rule forwards the requests from different domain names or URLs to different backend server groups.
    • A forwarding rule is composed of a domain name and URL.
    • A listener can have up to 40 forwarding rules.
    • You can configure a domain-based or URL-based forwarding rule for a load balancer. You can add multiple forwarding rules to a listener and associate these rules with different backend server groups.
    • A forwarding rule is matched by using the exact match and fuzzy match mechanisms. If multiple forwarding rules are matched, the forwarding rule matched through the exact match mechanism is used.
  • Certificate: If you select HTTPS for a listener, associate it with a certificate to make the listener take effect. You can upload either a certificate or certificate chain.
  • Backend server group: A backend server group is a group of backend servers that handles requests distributed by load balancers. It is the basic unit for traffic distribution by load balancer instances.
    • A load balancer can be associated with multiple backend server groups, while a backend server group can be associated with only one load balancer.
    • A backend server group can be associated with multiple listeners in the same load balancer.
    • Creating a load balancer will automatically create an empty backend server group.
  • Backend server: A backend server handles requests distributed by a load balancer. You can add a VM instance on the Cloud or a server on a third-party cloud as a backend server.