IPv6

Note:

Calico is the only CNI which supports IPv6 at this time.

As of Kubernetes 1.19, support for IPv6 is in beta and dual-stack(running clusters with both IPv4 and IPv6) is in alpha. Charmed Kubernetes supports both these features, though it is important to be familiar with the known issues described below.

Enabling IPv6 and dual-stack in Charmed Kubernetes

These features can be used simply by changing the configuration for Calico and the Kubernetes control-plane to include the relevant CIDRs.

For Calico, the cidr configuration can contain two comma-separated values, with the first CIDR in the list being the preferred family for pods.

For the Kubernetes control-plane, the service-cidr configuration can contain two comma-separated values, with the first being the default family for services.

Note that Kubernetes supports explicitly setting the ipFamilies for a service when creating it.

The following example shows how to deploy Charmed Kubernetes with IPv6 and dual-stack enabled.

Example deployment

You can use the following overlay file (download it here) along with charmed-kubernetes to enable IPv4-preferred dual-stack:

description: Charmed Kubernetes overlay to enable IPv4-IPv6 dual-stack.
applications:
  calico:
    options:
      cidr: "192.168.0.0/16,fd00:c00b:1::/112"
  kubernetes-control-plane:
    options:
      service-cidr: "10.152.183.0/24,fd00:c00b:2::/112"

Deploy with:

juju deploy charmed-kubernetes --overlay ipv4-ipv6-overlay.yaml

Once that is deployed, you can use the following spec (download it here) to run a dual-stack enabled nginx pod with an IPv6 service in front of it:

apiVersion: apps/v1
kind: Deployment
metadata:
  name: nginxdualstack
spec:
  selector:
    matchLabels:
      run: nginxdualstack
  replicas: 2
  template:
    metadata:
      labels:
        run: nginxdualstack
    spec:
      containers:
      - name: nginxdualstack
        image: rocks.canonical.com/cdk/diverdane/nginxdualstack:1.0.0
        ports:
        - containerPort: 80
---
apiVersion: v1
kind: Service
metadata:
  name: nginx6
  labels:
    run: nginxdualstack
spec:
  type: NodePort
  ipFamilies: [IPv6]
  ports:
  - port: 80
    protocol: TCP
  selector:
    run: nginxdualstack

Known Issues

Because of the pre-release feature status for IPv6 and dual-stack in Kubernetes and since Juju does not officially support IPv6, there are currently some things which won't work 100% and some limitations on IPv6 configuration. These will also vary depending on the underlying cloud provider.

Juju

The following arise because Juju does not fully support IPv6:

The charms require IPv4 on the underlying hosts, even when running a cluster in IPv6-only mode.
By default, connections to the API server will use the IPv4 address even when running a cluster in IPv6-preferred or IPv6-only mode. This can be modified in the client config by hand or overridden via the loadbalancer-ips config on the [kubernetes-control-plane] and / or [kubeapi-load-balancer] charms.
IPv6 NodePort listeners won't function on the master, though they will work on the worker units.
Juju's open-port cannot be used to allow NodePort connections for IPv6.

AWS

The following arise when using AWS as the underlying cloud provider:

Kubernetes creates classic load balancers for LoadBalancer-type services, which do not support IPv6.

Juju does not honor the "automatically assign IPv6 address" setting and creates instances without IPv6 addresses. You can attach IPv6 addresses after deploying with something like:

for machine in $(juju status --format=json | jq -r '.machines|keys[]' | sort -n); do
    echo -n "Machine $machine: "
    instance="pending"
    while [[ "$instance" == "pending" ]]; do
        instance=$(juju status --format=json | jq -r '.machines["'"$machine"'"]."instance-id"')
    done
    interface=$(aws ec2 describe-instances --instance-id "$instance" --output text --query 'Reservations[*].Instances[*].NetworkInterfaces[*].NetworkInterfaceId')
    aws ec2 modify-instance-attribute --instance-id "$instance" --no-source-dest-check
    ipv6_addresses=$(aws ec2 describe-instances --instance-id "$instance" --output text --query 'Reservations[*].Instances[*].NetworkInterfaces[*].Ipv6Addresses')
    if [[ -n "$ipv6_addresses" ]]; then
        echo "$ipv6_addresses"
    else
        aws ec2 assign-ipv6-addresses --network-interface-id "$interface" --ipv6-address-count 1 --output text --query 'AssignedIpv6Addresses'
    fi
done

OpenStack

No additional issues with IPv6 on OpenStack are known at this time.

MAAS

No additional issues with IPv6 on MAAS are known at this time.