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High availability group

BNS Load Balancing service provides a high availability group feature to ensure high availability. By grouping pre-created Application Load Balancer (ALB), Network Load Balancer (NLB), and Direct Server Return Network Load Balancer (DSRNLB) nodes across availability zones within a region, high availability can be achieved.

Create high availability group​

When creating a high availability group, you select a scheme, type, and VPC. Load balancer nodes (ALB, NLB, DSRNLB) that match these conditions can then be associated per availability zone to ensure high availability.
The scheme can be either Internet boundary, which allows communication over the internet using a public IP address, or Internal, which ensures high availability among load balancer nodes connected to private subnets.
The type refers to the load balancer type (ALB, NLB, DSRNLB).
Once a VPC is selected, one load balancer node is chosen for each subnet created in the availability zones of that VPC.

A high availability group can include at least one load balancer node, but to ensure high availability, it is recommended to connect two or more nodes.

Understand load balancer node​

All types of load balancers created through the KakaoCloud Console > Beyond Networking Service > Load Balancing > Load Balancer menu are referred to as load balancer nodes. These include Application Load Balancer, Network Load Balancer, and Direct Server Return Network Load Balancer.

When a high availability group is created, only load balancer nodes that match the specified type and scheme can be connected. They must also reside in private or public subnets within the same VPC but different availability zones.
Only one load balancer node can be connected per availability zone, and for high availability, at least two nodes in different zones must be connected.

A load balancer node already associated with a high availability group cannot be modified (e.g., connect or disconnect a public IP, or be deleted) until it is detached from the group.
Although each node can function independently, for applications that require high availability, it is recommended to configure and connect two or more identically configured nodes to a high availability group.

High availability group requirements​

To use the high availability group as a highly available load balancer after creation, the following requirements must be met:

  • At least two load balancer nodes must be connected to the high availability group. Although the group can be created with one node, high availability is not guaranteed in that case.
  • Each load balancer node connected to the group must match the scheme, type, and VPC defined for the group.
  • The detailed configuration of each connected node must be identical. This includes settings such as listener properties, maximum connection settings, and protocol.
  • Each connected load balancer node must be in a healthy, operating state.