Validate pod CIDR and service CIDR

[eaudetcobello]

We should verify that the user provides valid CIDRs when bootstrapping the cluster.

This PR adds validation at bootstrap-time.

• The Pod CIDR and Service CIDR do not overlap

• Are within Kubernetes CIDR limitations

Examples

bootstrap-config:

pod-cidr: 192.168.1.0/24
service-cidr: 192.168.2.0/24,fe80::/64

Error: Failed to validate the CIDR configuration.                                                                           

The error was: service CIDR "fe80::/64" cannot have a prefix length of 64 or more

bootstrap-config:

pod-cidr: 192.168.1.0/24
service-cidr: 192.168.1.0/24

Error: Failed to validate the CIDR configuration.                                                                             

The error was: pod CIDR "192.168.1.0/24" and service CIDR "192.168.1.0/24" overlap

[HomayoonAlimohammadi]

Wonderful job @eaudetcobello! Thanks a lot. Left some minor comments.

[HomayoonAlimohammadi]

/64 is too large for the Service CIDR: Using a /64 CIDR for services may cause issues like failure to initialize the IPv6 allocator.

This makes me feel that the problem might not only be with the IPv6 but that IPv6 problem is just an example, WDYT? Do we need to change the docs or check for IPv4 here as well?

[bschimke95]

That is a limitation of the Kubernetes controller. I understand your point, but IMHO we should describe the limitation for a user (-> use smaller CIDR size) as they normally don't care about the internals of some Kubernetes controller.

[eaudetcobello]

Did some tests with @berkayoz and we will be going with /108. Cluster fails to bootstrap at /64 and /96.

[bschimke95]

This check should be done on the server side (in the bootstrap hook) otherwise you'd need to implement this for every client.

[bschimke95]

looking good - couple of comments

[HomayoonAlimohammadi]

Thanks a lot @eaudetcobello! Left some minor comments.

[bschimke95]

LGTM, great work @eaudetcobello

[bschimke95]

please resolve the conflicts then this is good to merge

[HomayoonAlimohammadi]

LGTM, thanks a lot @eaudetcobello!