Subnet Auto Discovery¶
AWS Load Balancer controller auto discovers network subnets for ALB or NLB by default. ALB requires at least two subnets across Availability Zones, NLB requires one subnet.
The subnets must be tagged appropriately for the auto discovery to work. The controller chooses one subnet from each Availability Zone. In case of multiple tagged subnets in
an Availability Zone, the controller will choose the first one in lexicographical order by the Subnet IDs. If you use eksctl or an Amazon EKS AWS CloudFormation template to
create your VPC after March 26, 2020, then the subnets are tagged appropriately when they're created. For more information about the Amazon EKS AWS CloudFormation VPC templates,
see Creating a VPC for your Amazon EKS cluster.
Public subnets¶
Public subnets are used for internet-facing load balancers. These subnets must have the following tags:
| Key | Value |
|---|---|
kubernetes.io/role/elb |
1 or `` |
Private subnets¶
Private subnets are used for internal load balancers. These subnets must have the following tags:
| Key | Value |
|---|---|
kubernetes.io/role/internal-elb |
1 or `` |
Common tag¶
Both the public and private subnets must be tagged with the cluster name as follows:
| Key | Value |
|---|---|
kubernetes.io/cluster/${cluster-name} |
owned or shared |
${cluster-name} is the name of the kubernetes cluster