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Dual-stack support with kubeadm
Kubernetes v1.21 [beta]
Your Kubernetes cluster can run in dual-stack networking mode, which means that cluster networking lets you use either address family. In a dual-stack cluster, the control plane can assign both an IPv4 address and an IPv6 address to a single Pod or a Service.
Before you begin
You need to have installed the kubeadm tool, following the steps from Installing kubeadm.
For each server that you want to use as a node, make sure it allows IPv6 forwarding. On Linux, you can set this by running run sysctl -w net.ipv6.conf.all.forwarding=1
as the root user on each server.
You need to have an IPv4 and and IPv6 address range to use. Cluster operators typically
use private address ranges for IPv4. For IPv6, a cluster operator typically chooses a global
unicast address block from within 2000::/3
, using a range that is assigned to the operator.
You don't have to route the cluster's IP address ranges to the public internet.
The size of the IP address allocations should be suitable for the number of Pods and Services that you are planning to run.
Note: If you are upgrading an existing cluster then, by default, thekubeadm upgrade
command changes the feature gateIPv6DualStack
totrue
if that is not already enabled.
However,kubeadm
does not support making modifications to the pod IP address range (“cluster CIDR”) nor to the cluster's Service address range (“Service CIDR”).
Create a dual-stack cluster
To create a dual-stack cluster with kubeadm init
you can pass command line arguments
similar to the following example:
# These address ranges are examples
kubeadm init --pod-network-cidr=10.244.0.0/16,2001:db8:42:0::/56 --service-cidr=10.96.0.0/16,2001:db8:42:1::/112
To make things clearer, here is an example kubeadm
configuration file kubeadm-config.yaml
for the primary dual-stack control plane node.
---
apiVersion: kubeadm.k8s.io/v1beta2
kind: ClusterConfiguration
featureGates:
IPv6DualStack: true
networking:
podSubnet: 10.244.0.0/16,2001:db8:42:0::/56
serviceSubnet: 10.96.0.0/16,2001:db8:42:1::/112
---
apiVersion: kubeadm.k8s.io/v1beta2
kind: InitConfiguration
localAPIEndpoint:
advertiseAddress: "10.100.0.1"
bindPort: 6443
nodeRegistration:
kubeletExtraArgs:
node-ip: 10.100.0.2,fd00:1:2:3::2
advertiseAddress
in InitConfiguration specifies the IP address that the API Server will advertise it is listening on. The value of advertiseAddress
equals the --apiserver-advertise-address
flag of kubeadm init
Run kubeadm to initiate the dual-stack control plane node:
kubeadm init --config=kubeadm-config.yaml
Currently, the kube-controller-manager flags --node-cidr-mask-size-ipv4|--node-cidr-mask-size-ipv6
are being left with default values. See enable IPv4/IPv6 dual stack.
Note: The--apiserver-advertise-address
flag does not support dual-stack.
Join a node to dual-stack cluster
Before joining a node, make sure that the node has IPv6 routable network interface and allows IPv6 forwarding.
Here is an example kubeadm configuration file
kubeadm-config.yaml
for joining a worker node to the cluster.
apiVersion: kubeadm.k8s.io/v1beta2
kind: JoinConfiguration
discovery:
bootstrapToken:
apiServerEndpoint: 10.100.0.1:6443
nodeRegistration:
kubeletExtraArgs:
node-ip: 10.100.0.3,fd00:1:2:3::3
Also, here is an example kubeadm configuration file
kubeadm-config.yaml
for joining another control plane node to the cluster.
apiVersion: kubeadm.k8s.io/v1beta2
kind: JoinConfiguration
controlPlane:
localAPIEndpoint:
advertiseAddress: "10.100.0.2"
bindPort: 6443
discovery:
bootstrapToken:
apiServerEndpoint: 10.100.0.1:6443
nodeRegistration:
kubeletExtraArgs:
node-ip: 10.100.0.4,fd00:1:2:3::4
advertiseAddress
in JoinConfiguration.controlPlane specifies the IP address that the API Server will advertise it is listening on. The value of advertiseAddress
equals the --apiserver-advertise-address
flag of kubeadm join
.
kubeadm join --config=kubeadm-config.yaml ...
Create a single-stack cluster
Note: Enabling the dual-stack feature doesn't mean that you need to use dual-stack addressing.
You can deploy a single-stack cluster that has the dual-stack networking feature enabled.
In 1.21 the IPv6DualStack
feature is Beta and the feature gate is defaulted to true
. To disable the feature you must configure the feature gate to false
. Note that once the feature is GA, the feature gate will be removed.
kubeadm init --feature-gates IPv6DualStack=false
To make things more clear, here is an example kubeadm
configuration file
kubeadm-config.yaml
for the single-stack control plane node.
apiVersion: kubeadm.k8s.io/v1beta2
kind: ClusterConfiguration
featureGates:
IPv6DualStack: false
networking:
podSubnet: 10.244.0.0/16
serviceSubnet: 10.96.0.0/16
What's next
- Validate IPv4/IPv6 dual-stack networking
- Read about Dual-stack cluster networking
- Learn more about the kubeadm configuration format