Load Balancer
Load Balancer
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Load BalancerApplication Load Balancer (ALB)User GuideInstanceOverview
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Download PDFCopy pageDownload PDFTo use the ALB service, you need to create an ALB instance first. An ALB instance is the specific load balancer that you can configure and manage. The ALB instance receives requests from clients and distributes them to backend servers according to the forwarding rules and load balancing policies you set.
Instance network types
ALB instances are divided into two types: Internet-facing instances and private instances. You can create Internet-facing or private instances based on your usage scenarios.
Internet-facing instances
When you create an Internet-facing instance, it obtains both an EIP and a private IP address. The EIP enables the instance to handle requests from clients on the Internet. The private IP address enables the instance to handle requests from clients within VPCs.
Private instances
When you create a private instance, it only obtains a private IP address and can only handle requests from clients within VPCs.
IP address types of instances
ALB instances support two IP address types: IPv4 and IPv4/IPv6 dual stack.
IP Address Type | Internet-facing ALB Instance | Private ALB Instance | Description |
|---|---|---|---|
IPv4 | An Internet-facing ALB instance has one public IPv4 address and one private IPv4 address in each of the availability zones to which it belongs. | A private ALB instance has one private IPv4 address in each of the availability zones to which it belongs. | If the IP address type of an ALB instance is IPv4, clients can only access the ALB instance using IPv4 addresses. |
IPv4/IPv6 dual stack | An Internet-facing ALB instance has one public IPv4 address, one private IPv4 address, and one IPv6 address in each of the availability zones to which it belongs. The IPv6 address serves as both public and private IP address. | A private ALB instance has one private IPv4 address and one private IPv6 address in each of the availability zones to which it belongs. | If the IP address type of an ALB instance is IPv4/IPv6 dual stack, clients can access the ALB instance using either IPv4 or IPv6 addresses. |
tip
If the IP address type of an ALB instance is IPv4/IPv6 dual stack, the following restrictions apply:
- The network type of the instance cannot be changed.
- To use dual-stack ALB instances, please contact your account manager or submit a ticket.
Instance domain name
After you create an ALB instance, the system not only assigns IP addresses to the instance but also assigns a unique domain name. The format of the instance domain name is: instanceId.regionId.volcenginealb.com. For example: alb-abc123def456.cn-beijing.volcenginealb.com.
You can use a custom domain name that is easier to member such as www.example.com, and then associate it with the instance domain name using a CNAME record. When a client initiates a request using the custom domain name, the DNS server resolves the custom domain name to the instance domain name. For information on how to add a CNAME record, see Add a CNAME record pointing to an instance domain name.
Availability zones and instance nodes
When creating an ALB instance, you must select a region and one or more availability zones for the ALB instance. When there are multiple availability zones in the region where the ALB instance is located, it is recommended that you deploy the ALB instance to at least two availability zones. This way, when one availability zone is unavailable or has no available backend servers, ALB will forward requests to backend servers in another availability zone, ensuring business continuity. For more information about regions and availability zones, see Regions and availability zones.
When an ALB instance is deployed to multiple availability zones, there will be an instance node in each availability zone. Under normal circumstances, client traffic is evenly distributed to each instance node.
Cross-zone load balancing
The "cross-zone load balancing" feature at the ALB instance level is enabled by default and cannot be disabled. By default, instance nodes in one availability zone distribute received requests to backend servers in all availability zones where the ALB instance is deployed.
You can disable the "cross-zone load balancing" feature at the server group level. After this feature is disabled, an instance node will only distribute received requests to backend servers in the same availability zone.
For more information about the "cross-zone load balancing" feature, see Cross-zone load balancing.
