Subnet auto-discovery¶
By default, the AWS Load Balancer Controller (LBC) auto-discovers network subnets that it can create AWS Network Load Balancers (NLB) and AWS Application Load Balancers (ALB) in. ALBs require at least two subnets across Availability Zones. NLBs require one subnet.
The subnets must be tagged appropriately for auto-discovery to work. The controller chooses one subnet from each Availability Zone. During auto-discovery, the controller
considers subnets with at least eight available IP addresses. In the case of multiple qualified tagged subnets in an Availability Zone, the controller chooses the first one in lexicographical
order by the subnet IDs.
For more information about the subnets for the LBC, see Application Load Balancers
and Network Load Balancers.
If you used 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¶
In version v2.1.1 and older of the LBC, 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.
The cluster tag is not required in versions v2.1.2 to v2.4.1, unless a cluster tag for another cluster is present.
With versions v2.4.2 and later, you can disable the cluster tag check completely by specifying the feature gate SubnetsClusterTagCheck=false