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Server Load Balancer:What is ALB?

Last Updated:Apr 18, 2024

Application Load Balancer (ALB) is an Alibaba Cloud service that runs at the application layer and is optimized to balance traffic over HTTP, HTTPS, and Quick UDP Internet Connections (QUIC). ALB is highly elastic and can process large volumes of Layer 7 traffic on demand. ALB supports complex routing and is integrated with other cloud-native services. ALB is designed as an ingress gateway to manage inbound traffic on Alibaba Cloud.


Why ALB?

As a cloud-native ingress gateway on Alibaba Cloud, ALB is developed for Layer 7 load balancing over HTTP, HTTPS, and QUIC and provides advanced routing features. For more information about ALB Ingresses, see ALB Ingress overview and ALB Ingress user guide.

  • Application layer elasticity
    ALB is developed for Layer 7 load balancing and provides domain names and virtual IP addresses to handle large amounts of network traffic at multiple levels. ALB distributes network traffic across backend server groups to improve the availability of applications and prevent service interruptions caused by single points of failure (SPOFs). ALB supports custom cross-zone deployment and elastic scaling across zones to remove resource bottlenecks in individual zones.
  • Advanced protocols
    ALB supports HTTP, HTTPS, and QUIC and can process a heavy load of network traffic. You can use ALB to provide fast and secure connections to mobile Internet applications, such as real-time audio and video applications, interactive streaming applications, and online gaming applications. ALB supports Google Remote Procedure Call (gRPC) to facilitate efficient communication among microservices through APIs.
  • Content-based routing
    ALB can route network traffic to different backend servers based on the request content, such as the path, HTTP header, query string, HTTP request method, cookie, and source IP address. ALB also supports advanced configurations, such as redirects, rewrites, and custom HTTPS headers.
  • Security and reliability
    ALB supports DDoS mitigation and can be integrated with Web Application Firewall (WAF) to provide more security features. In addition, ALB supports end-to-end HTTPS encryption, custom security policies, and efficient encryption protocols, such as TLS 1.3. ALB protects your business-critical services and complies with the Zero Trust security framework.
  • Cloud-native
    As more cloud-native services are developed, a growing number of customers in the Internet, finance, and enterprise sectors deploy applications in the cloud or migrate existing business systems to the cloud. As a cloud-native ingress gateway for Alibaba Cloud, ALB is deeply integrated with Container Service for Kubernetes (ACK), Serverless App Engine (SAE), Function Compute, and Kubernetes.
  • Flexible billing
    ALB uses elastic IP addresses (EIPs) and Internet Shared Bandwidth instances to provide Internet-facing services and supports flexible billing for Internet data transfer. ALB also supports the pay-by-LCU metering method, which is ideal for services with traffic spikes.

Performance metrics

ALB supports the dynamic IP and static IP modes. The performance of an ALB instance varies based on the IP mode.


The performance metrics of an ALB instance vary only based on the IP mode of the ALB instance, and are not affected by the edition of the ALB instance.

Performance of an ALB instance deployed in two zones

IP mode

Maximum queries per second (QPS)

Maximum number of new connections (CPS)

Maximum number of concurrent connections

Maximum internal bandwidth

Default Internet bandwidth

Dynamic IP

1 million

1 million

10 million

100 Gbit/s

400 Mbit/s. The actual Internet bandwidth varies based on the total bandwidth of the EIPs associated with an ALB instance.

  • The sum of the maximum bandwidth of all pay-by-data-transfer EIPs in each Alibaba Cloud account in each region cannot exceed 5 Gbit/s. For more information, see the bandwidth limits in Pay-as-you-go.

  • If you want to use larger bandwidth, purchase an Internet Shared Bandwidth instance. For more information about how to purchase an Internet Shared Bandwidth instance, see Create an Internet Shared Bandwidth instance.

Static IP



1 million

10 Gbit/s

  • In a multi-zone region, the default maximum QPS of an ALB instance is 100,000, which does not change with the number of zones. The maximum QPS of an ALB instance in static IP mode is 100,000. The maximum QPS of an ALB instance in dynamic IP mode automatically scales up to 1 million.

  • We recommend that you use CNAME records to map custom domain names to the domain name of an ALB instance. This way, the ALB instance can provide external services. If you use this method, ALB can provide a service uptime of up to 99.995%.

  • ALB supports multi-zone deployment. If the current region contains two or more zones, you must select at least two zones to ensure high availability. If you select multiple zones for an ALB instance, you are not charged additional fees.

ALB components





ALB provides ultra-high Layer 7 processing capabilities and can increase the service capacity of your applications by distributing network traffic across different backend servers. Each ALB instance supports up to 1 million QPS.


A listener is the smallest configurable unit of ALB. Listeners listen for requests over the protocols and ports that you configure. For example, you can configure a listener of ALB to process HTTP requests on port 80. You must add at least one listener to each ALB instance before the ALB instance can distribute network traffic. By default, you can add up to 50 listeners to each ALB instance to distribute network traffic for different workloads.

Forwarding rule

ALB distributes requests to backend servers in one or more server groups based on forwarding rules. ALB provides advanced routing features. In addition to the basic routing features, you can specify conditions such as the HTTP header, cookie, and HTTP method in a forwarding rule to route network traffic to different backend servers.

Server group

Backend servers can be organized into logical groups (also known as server groups) to which requests are distributed. Each server group contains one or more backend servers that process requests distributed by ALB. Server groups of ALB are independent of ALB. You can associate a server group with different ALB instances. By default, you can specify up to 1,000 backend servers in each server group. ALB supports multiple types of backend servers, such as Elastic Compute Service (ECS) instances, elastic container instances, and elastic network interfaces (ENIs).

Health check

ALB checks the availability of backend servers by performing health checks. If a backend server is declared unhealthy, ALB does not forward requests to the backend server. ALB supports flexible health check configurations. For example, you can specify the protocol, port, and thresholds for health checks. ALB provides health check templates that can be applied to different server groups.

Types of ALB instances

Alibaba Cloud provides Internet-facing and internal-facing ALB instances. You can specify the type of ALB instance based on your business requirements. Whether EIPs and Internet Shared Bandwidth instances are used is based on the specified type of ALB instance.




Internet Shared Bandwidth instance

Internet Shared Bandwidth instances allow you to share and transfer bandwidth resources within the same region. Internet Shared Bandwidth instances support multiple metering methods such as pay-by-bandwidth and pay-by-enhanced-95th-percentile. You can use Internet Shared Bandwidth instances to reduce Internet bandwidth costs. Internet-facing ALB instances use Internet Shared Bandwidth instances that support the pay-by-bandwidth and pay-by-enhanced-95th-percentile metering methods to provide Internet-facing services.

Domain name

A domain name can be accessed over the Internet or private networks and can be resolved to the virtual IP address (VIP) of an ALB instance. You can also create a CNAME record to map a readable domain name to the domain name of ALB. For more information, see Configure a CNAME record.


EIPs are required only by Internet-facing ALB instances. You do not need to associate EIPs with internal-facing ALB instances. An EIP is an IP address that ALB uses to provide services over the Internet. You can associate multiple EIPs with an Internet-facing ALB instance. To ensure high availability, an Internet-facing ALB instance must use at least two EIPs in different zones to provide services.


VIPs of ALB are used to receive and forward requests. Each VIP is a private IP address that belongs to a virtual private cloud (VPC).

Activate ALB

To activate ALB, click the following button to go to the ALB buy page.

Create ALB instances

Deploy and maintain ALB instances

After you create an Alibaba Cloud account, you can deploy and manage ALB instances in the following ways:

  • ALB console: a web interface that you can use to manage your ALB service. You can create, use, or release ALB instances in the console. For more information, see Create an ALB instance.

  • Alibaba Cloud SDKs: SDKs for Java, Go, Python, and other programming languages.

  • OpenAPI Explorer: allows you to retrieve and call API operations, and dynamically generate SDK sample code.

  • Terraform: helps you implement version control for cloud and on-premises resources. You can use Terraform configuration files to orchestrate resources on Alibaba Cloud and other cloud service platforms that support Terraform.