MultiClusterCIDR for v1.26

[rbrtbnfgl]

Proposed Changes

Types of Changes

New Feature

Verification

Testing

To start a K3s cluster with multi cluster CIDR enabled use the flag --multi-cluster-cidr and the clustercidrs should be visible through the API and kubectl to configure a new cluster CIDR follow flannel documentation https://github.com/flannel-io/flannel/tree/master/Documentation/MultiClusterCIDR#configure-the-required-clustercidr-resources

DualStack setup could have issues related to the different address spaces between IPv4 and IPv6 that should be the same.

Linked Issues

#6443

User-Facing Change

MultiClusterCIDR feature

Further Comments

[dereknola]

Is it possible to consolidate the 2 E2E tests you wrote into a single IPv4 + IPv6 test?

[brandond]

How does this behave if the user enables it but does not create a ClusterCIDR resource? Is a default one created from the legacy cluster/service cidr args?

[rbrtbnfgl]

How does this behave if the user enables it but does not create a ClusterCIDR resource? Is a default one created from the legacy cluster/service cidr args?

When the flag is enabled a first ClusterCIDR resource is created based on the --cluster-cidr defined and the Kube-controller will always use it to allocate the CIDRs for each node.

[rbrtbnfgl]

@brandond Do we want to keep this on hold and merge only the flannel version update for the next release?

[brandond]

@rbrtbnfgl yeah lets just do the flannel version bump for now, I think the multi-ClusterCIDR stuff is probably worth at least a talk through in design review.