ELB Types

Introduction to ELB

Elastic Load Balance (ELB) automatically distributes incoming traffic across servers to balance their workloads, increasing the service capabilities and fault tolerance of your applications.

Load Balancer Types

ELB provides shared load balancers and dedicated load balancers for you to choose from.

**Table 1** Load balancer types
Item	Dedicated Load Balancer	Shared Load Balancer
Deployment mode	You get exclusive access to load balancer resources. The performance of a dedicated load balancer is never affected by the loads on other load balancers. In addition, there are a wide range of specifications available for you to choose from.	They are deployed in clusters and share resources with other instances. They support guaranteed performance.
Specifications	Elastic specifications: You are charged for how long each load balancer is running and the number of LCUs you use. Fixed specifications: Multiple specifications are available for you to select to best meet your needs. For details, see Specifications of Dedicated Load Balancers.	N/A
Performance	A dedicated load balancer in an AZ can establish up to 20 million concurrent connections. If you deploy a dedicated load balancer in two AZs, the number of concurrent connections will be doubled. For example, if you deploy a dedicated load balancer in two AZs, it can handle up to 40 million concurrent connections.	If guaranteed performance is enabled, shared load balancers can handle up to 50,000 concurrent connections, 5,000 new connections per second, and 5,000 queries per second.
AZ	You can select one or more AZs as needed. If requests are from the Internet, the load balancer in each AZ you select routes the requests based on source IP addresses. If you deploy a load balancer in two AZs, the requests the load balancers can handle will be doubled. For requests from a private network: If clients are in the AZ you select when you create the load balancer, requests are distributed by the load balancer in this AZ. If the load balancer is unhealthy, requests are distributed by the load balancer in another AZ you select. If the load balancer is healthy but the connections that the load balancer needs to handle exceed the amount defined in the specifications, service may be interrupted. To address this issue, you need upgrade specifications. You can monitor traffic usage on private network by AZ. If clients are in an AZ that is not selected when you create the load balancer, requests are distributed by the load balancer in each AZ you select based on source IP addresses. If requests are from a Direct Connect connection, the load balancer in the same AZ as the Direct Connect connection routes the requests. If the load balancer is unavailable, requests are distributed by the load balancer in another AZ. If clients are in a VPC that is different from where the load balancer works, the load balancer in the AZ where the original VPC subnet resides routes the requests. If the load balancer is unavailable, requests are distributed by the load balancer in another AZ.	N/A
Billing item	Fixed specifications: billed by the LCUs based on the specifications you select. Elastic specifications: billed by how many LCUs you use and how long you use your load balancers	You are charged for how long you use each load balancer if guaranteed performance is enabled.

Feature Comparison

**Table 2** Feature comparison
Item	Dedicated Load Balancer	Shared Load Balancer
Capabilities	Powerful capabilities to process Layer 4 and Layer 7 requests, advanced forwarding policies, and multiple protocols.	Basic capabilities to process Layer 4 and Layer 7 requests
Application scenarios	Heavy-traffic and highly concurrent services, such as large websites, cloud-native applications, IoV, and multi-AZ disaster recovery applications	Services with low traffic, such as small websites and common HA applications
Frontend protocols	TCP, UDP, HTTP, TLS, and HTTPS	TCP, UDP, HTTP, and HTTPS
Backend protocols	TCP, UDP, HTTP, HTTPS, and QUIC	TCP, UDP, and HTTP
Forwarding capabilities	Provide powerful Layer 4 and Layer 7 processing capabilities to forward requests based on the following: Forwarding rules: domain name, path, HTTP request method, HTTP header, query string, and CIDR block Actions: forward to a backend server group, redirect to another listener, redirect to another URL, rewrite, and return a specific response body	Provide basic Layer 4 and Layer 7 processing capabilities to forward requests based on the following: Forwarding rules: domain name and path Actions: forward to a backend server group and redirect to another listener
Key functions of backend server groups	Health check Sticky session Slow start	Health check Sticky session
Load balancing algorithms	Weighted round robin Weighted least connections Source IP hash Connection ID	Weighted round robin Weighted least connections Source IP hash
Forwarding modes of backend server groups	Load balancing Active/Standby	Load balancing
Backend type	ECS IP as backend server Supplementary network interface BMS CCE Turbo cluster	ECS BMS CCE Turbo cluster