VPC Networking

VPC Networking

By default, eksctl create cluster will build a dedicated VPC, in order to avoid interference with any existing resources for a variety of reasons, including security, but also because it’s challenging to detect all the settings in an existing VPC. Default VPC CIDR used by eksctl is 192.168.0.0/16, it is divided into 8 (/19) subnets (3 private, 3 public & 2 reserved). Initial nodegroup is create in public subnets, with SSH access disabled unless --allow-ssh is specified. However, this implies that each of the EC2 instances in the initial nodegroup gets a public IP and can be accessed on ports 1025 - 65535, which is not insecure in principle, but some compromised workload could risk an access violation.

If that functionality doesn’t suit you, the following options are currently available.

Change VPC CIDR

If you need to setup peering with another VPC, or simply need larger or smaller range of IPs, you can use --vpc-cidr flag to change it. You cannot use just any sort of CIDR, there only certain ranges that can be used in AWS VPC.

Use private subnets for initial nodegroup

If you prefer to isolate initial nodegroup from the public internet, you can use --node-private-networking flag. When used in conjunction with --ssh-access flag, SSH port can only be accessed inside the VPC.

Use existing VPC: shared with kops

You can use a VPC of an existing Kubernetes cluster managed by kops. This feature is provided to facilitate migration and/or cluster peering.

If you have previously created a cluster with kops, e.g. using commands similar to this:

export KOPS_STATE_STORE=s3://kops
kops create cluster cluster-1.k8s.local --zones=us-west-2c,us-west-2b,us-west-2a --networking=weave --yes

You can create an EKS cluster in the same AZs using the same VPC subnets (NOTE: at least 2 AZs/subnets are required):

eksctl create cluster --name=cluster-2 --region=us-west-2 --vpc-from-kops-cluster=cluster-1.k8s.local

Use existing VPC: any custom configuration

Use this feature if you must configure a VPC in a way that’s different to how dedicated VPC is configured by eksctl, or have to use a VPC that already exists so your EKS cluster gets shared access to some resources inside that existing VPC, or you have any other use-case that requires you to manage VPCs separately.

You can use an existing VPC by supplying private and/or public subnets using --vpc-private-subnets and --vpc-public-subnets flags. It is up to you to ensure which subnets you use, as there is no simple way to determine automatically whether a subnets is private or public, because configurations vary. Given these flags, eksctl create cluster will determine the VPC ID automatically, but it will not create any routing tables or other resources, such as internet/NAT gateways. It will, however, create dedicated security groups for the initial nodegroup and the control plane.

You must ensure to provide at least 2 subnets in different AZs. There are other requirements that you will need to follow, but it’s entirely up to you to address those. For example, tagging is not strictly necessary, tests have shown that its possible to create a functional cluster without any tags set on the subnets, however there is no guarantee that this will always hold and tagging is recommended.

  • all subnets in the same VPC, within the same block of IPs
  • sufficient IP addresses are available
  • sufficient number of subnets (minimum 2)
  • internet and/or NAT gateways are configured correctly
  • routing tables have correct entries and the network is functional
  • tagging of subnets
    • kubernetes.io/cluster/<name> tag set to either shared or owned
    • kubernetes.io/role/internal-elb tag set to 1 for private subnets

There maybe other requirements imposed by EKS or Kubernetes, and it is entirely up to you to stay up-to-date on any requirements and/or recommendations, and implement those as needed/possible.

Default security group settings applied by eksctl may or may not be sufficient for sharing access with resources in other security groups. If you wish to modify the ingress/egress rules of the either of security groups, you might need to use another tool to automate changes, or do it via EC2 console.

If you are in doubt, don’t use a custom VPC. Using eksctl create cluster without any --vpc-* flags will always configure the cluster with a fully-functional dedicated VPC.

To create a cluster using 2x private and 2x public subnets, run:

eksctl create cluster \
  --vpc-private-subnets=subnet-0ff156e0c4a6d300c,subnet-0426fb4a607393184 \
  --vpc-public-subnets=subnet-0153e560b3129a696,subnet-009fa0199ec203c37

To create a cluster using 3x private subnets and make initial nodegroup use those subnets, run:

eksctl create cluster \
  --vpc-private-subnets=subnet-0ff156e0c4a6d300c,subnet-0549cdab573695c03,subnet-0426fb4a607393184 \
  --node-private-networking

To create a cluster using 4x public subnets, run:

eksctl create cluster \
  --vpc-public-subnets=subnet-0153e560b3129a696,subnet-0cc9c5aebe75083fd,subnet-009fa0199ec203c37,subnet-018fa0176ba320e45

Custom Cluster DNS address

There are two ways of overwriting the DNS server IP address used for all the internal and external DNs lookups (this is, the equivalent of the --cluster-dns flag for the kubelet).

The first, is through the clusterDNS field. Config files accept a string field called clusterDNS with the IP address of the DNS server to use. This will be passed to the kubelet that in turn will pass it to the pods through the /etc/resolv.conf file.

apiVersion: eksctl.io/v1alpha5
kind: ClusterConfig

metadata:
  name: cluster-1
  region: eu-north-1

nodeGroups:
- name: ng-1
  clusterDNS: 169.254.20.10

Note that this configuration only accepts one IP address. To specify more than one address, use the extraKubeletConfig parameter:

apiVersion: eksctl.io/v1alpha5
kind: ClusterConfig

metadata:
  name: cluster-1
  region: eu-north-1

nodeGroups:
  - name: ng-1
    kubeletExtraConfig:
        clusterDNS: ["169.254.20.10","172.20.0.10"]

NAT Gateway

The NAT Gateway for a cluster can be configured to be Disabled, Single (default) or HighlyAvailable. It can be specified through the --vpc-nat-mode CLI flag or in the cluster config file like the example below:

vpc:
  nat:
    gateway: HighlyAvailable # other options: Disable, Single (default)

See the complete example here.

Note: Specifying the NAT Gateway is only supported during cluster creation and it is not touched during a cluster upgrade. There are plans to support changing between different modes on cluster update in the future.

Managing Access to the Kubernetes API Server Endpoints

The default creation of an EKS cluster exposes the Kubernetes API server publicly but not directly from within the VPC subnets (public=true, private=false). Traffic destined for the API server from within the VPC must first exit the VPC networks (but not Amazon’s network) and then re-enter to reach the API server.

The Kubernetes API server endpoint access for a cluster can be configured for public and private access when creating the cluster using the cluster config file. Example below:

vpc:
  clusterEndpoints:
    publicAccess:  <true|false>
    privateAccess: <true|false>

There are some additional caveats when configuring Kubernetes API endpoint access:

  1. EKS doesn’t allow one to create or update a cluster without at least one of private or public access being enabled.
  2. EKS does allow creating a configuration which allows only private access to be enabled, but eksctl doesn’t support it during cluster creation as it prevents eksctl from being able to join the worker nodes to the cluster.
  3. To create private-only Kubernetes API endpoint access, one must first create the cluster with public Kubernetes API endpoint access, and then use eksctl utils update-cluster-endpoints to change it after the cluster is finished creating.
  4. Updating a cluster to have private only Kubernetes API endpoint access means that Kubernetes commands (e.g. kubectl) as well as eksctl delete cluster, eksctl utils write-kubeconfig, and possibly the command eksctl utils update-kube-proxy must be run within the cluster VPC. This requires some changes to various AWS resources. See: EKS user guide

The following is an example of how one could configure the Kubernetes API endpoint access using the utils sub-command:

eksctl utils update-cluster-endpoints --name=<clustername> --private-access=true --public-access=false

Note that if you don’t pass a flag in it will keep the current value. Once you are satisfied with the proposed changes, add the approve flag to make the change to the running cluster.