Shorten NS names for zone delegation

[somaritane]

As of now, k8gb constructs NS name for delegated zone from the following chunks:

gslb-ns-<FlatDNSZone>-<ClusterGeoTag>.<EdgeDNSZone>, where
FlatDNSZone is DNSZone with '.'s replaced by '-'s, e.g. cloud.example.com -> cloud-example-com

so for

DNSZone = cloud.example.com 
ClusterGeoTag = eu
EdgeDNSZone = example.com

resulting NS server name looks like:

gslb-ns-cloud-example-com-eu.example.com

max length of DNS label is 63 characters
which leaves max allowed length for <ConvertedDNSZone>-<ClusterGeoTag> at 55 characters.

While it might be enough for relatively short DNSZones, like cloud.example.com,
for longer DNSZones it might quickly exceed the 55 characters limit and lead to delegated zone request error from EdgeDNS:

k8gb-77bf5b98f4-lwxm8 k8gb 2021/04/22 10:06:49 WAPI request error: 400('400 Bad Request')
k8gb-77bf5b98f4-lwxm8 k8gb Contents:
k8gb-77bf5b98f4-lwxm8 k8gb { "Error": "AdmConDataError: A domain label is longer than 63 characters",
k8gb-77bf5b98f4-lwxm8 k8gb   "code": "Client.Ibap.Data",
k8gb-77bf5b98f4-lwxm8 k8gb   "text": "A domain label is longer than 63 characters"
k8gb-77bf5b98f4-lwxm8 k8gb }

Logic to construct NS should be improved to give max possible room for DNS zone, while keep NS names unique
k8gb documentation should reflect the limits for DNSZone+ClusterGeoTag combination

[kuritka]

@somaritane

• This is infoblox case, for the consistency, should be the same logic applied to the other providers?

• Imagine we have three regions:

eu                              # valid
us                              # valid
long-invalid-region-name-123456 # invalid, too long

GSLB shouldn't start for region eu , because we know that long-invalid-region-name will fail anyway.

[somaritane]

@kuritka it's not Infoblox-specific case, 63-character length limit for DNS labels is imposed by RFC 1035

[somaritane]

Regarding validation, I think there should be synthetic length validation for combination of chunks in NS label (max 55 chars), it is then up to user to pick the right balance of chunk sizes.