Update README and example variables regarding subnet tags

In Kubernetes v1.21, tagging subnets is not required to create load
balancers. Keights will still support tagging them. See
kubernetes/kubernetes#97431.

stack/ansible/example/vars.yml

@@ -73,17 +73,10 @@ ssh_access_cidr: 0.0.0.0/0
 # CIDR which is given access to the API server
 api_access_cidr: 0.0.0.0/0
 
-# Define subnet tags so Kubernetes can build load balancers. The value
-# `internal-elb` can be changed to `elb` to allow internet facing load balancers.
-# The odd quoting is due to having the `cluster` variable in the key of a dictionary.
-cluster_tag_name: 'kubernetes.io/cluster/{{ cluster }}'
-subnet_tags: "{{ { cluster_tag_name: 'shared', 'kubernetes.io/role/internal-elb': '1' } }}"
-
 # A list of configurations for each node group. Add as many
 # node groups as you want to the list below.
 node_groups:
 - subnet_ids: '{{ node_subnet_ids }}'
-  subnet_tags: '{{ subnet_tags }}'
   # The name must be unique for each group
   name: app
   min_instances: 2

stack/ansible/keights-stack/README.md

@@ -162,7 +162,7 @@ All role variables go under a top level dictionary `keights_stack`.
 
 `kubeadm_join_config_template`: (Optional, type *string*, default `''`) - A kubeadm join [configuration file](https://kubernetes.io/docs/reference/setup-tools/kubeadm/kubeadm-join/#config-file) as a Go template string. If not defined, a default one will be used which is built into the AMI. See [Kubeadm join](#kubeadm-join) below for a description of the variables that will be available within the template. Due to CloudFormation parameter limitations, this string must not be over 4kb.
 
-`subnet_tags`: (Optional, type *dict*, default `{}`) - A dictionary of tags to add to node subnets. For example `{'kubernetes.io/cluster/cb': 'shared', 'kubernetes.io/role/internal-elb': '1'}`, where `cb` is the name of the cluster; this would allow the `cb` cluster to create internal ELBs in the node subnets. This is documented fully in the [EKS documentation](https://docs.aws.amazon.com/eks/latest/userguide/network_reqs.html#vpc-subnet-tagging), though it is not specific to EKS.
+`subnet_tags`: (Optional, type *dict*, default `{}`) - A dictionary of tags to add to node subnets. For example `{'kubernetes.io/cluster/cb': 'shared', 'kubernetes.io/role/internal-elb': '1'}`, where `cb` is the name of the cluster; this would allow the `cb` cluster to create internal ELBs in the node subnets. This is documented fully in the [EKS documentation](https://docs.aws.amazon.com/eks/latest/userguide/network_reqs.html#vpc-subnet-tagging), though it is not specific to EKS. Note that [as of Kubernetes v1.21](https://github.com/kubernetes/kubernetes/pull/97431), tagging of subnets is not required although it is still supported.
 
 `spot`: (Optional, type *dict*, default `{}`) - A dictionary of options pertaining to spot instances, described below.