Refactor to providers

[kuritka]

GslbAssistant

IDNSProvider

• implementation Route53, NS1
• having two functions (HandleZoneDelegation, Finalize)
• implement ExternalDNSProvider
• GetGSLBIngressIPs -> GslbIngressExposedIPs
• EnsureDNSEndpoint -> SaveDNSEndpoint
• RemoveEndpoint

Create private functions in providers/dns package

• nsServerName
• nsServerNameExt
• getExternalClusterHeartbeatFQDNs
• cover all of them by tests

GslbAssistant

• implementis IGslbAssistant interface
• common functionality for providers mostly exposes endpoints CRUD
• accepts Logger interface and could log
• GetGSLBIngressIPs -> GslbIngressExposedIPs
• EnsureDNSEndpoint -> SaveDNSEndpoint
• add RemoveEndpoint
• checkTXTRecord moved to assistant, fixed tests; renamed to InspectTXTThreshold
• remove gslb parameter from assistant.RemoveEndpoint
• remove error output argument from GetExternalTargets
• overrideWithFakeDNS moved to assistant as private func
• accepts Logger interface and could log

IDNSProvider

• implementation Route53, NS1
• having two functions (HandleZoneDelegation, Finalize)
• implement ExternalDNSProvider
• DNSProvider.SaveDNSEndpoint instead of ensureDNSEndpoint

ExternalDNS:

• move CreateZoneDelegationForExternalDNS to ExternalDNS
• fixed, missing finalizer for NS1 (Missing finalizer for NS1 #262)
• fix tests, If config is modified, new provider needs to be re-created. There is no way and reason to change provider
  configuration at another time than startup

Infoblox:

• split infoblox logic into three package files
• integrate Infoblox, audit logger fix, no log.Info(fmt.Srintf(...)) needed now, audit.Info(..) takes care..
• InfobloxDNSProvider contains InfobloxConnection; fakeInfobloxConnection

EmptyDNS

• Finalize runs this: p.assistant.RemoveEndpoint(gslb.Name)
• CreateZoneDelegationForExternalDNS returns nil;
• The rest is implemented the very same way as ExternalDNSPRovider

DNS package tests

• TestCanGenerateExternalHeartbeatFQDNs moved to dns package
• TestCanFilterOutDelegatedZoneEntryAccordingFQDNProvided moved from controller-tests to infoblox
• TestGeneratesProperExternalNSTargetFQDNsAccordingToTheGeoTags moved to common_test but no completely refactored

Other:

• deprecated NewGone() to NewResourceExpired()
• implement Stringer interface by providers; now fmt.Sprintf(%s,providerInstance) is writes meaningful message

Factory implementation
Factory tests
Integrate factory with the rest of the code

• changes in main.go, instantiate IDNSProvider
• dnsupdate.go, remove CreateZoneDelegationForExternalDNS
• controller, using r.DNSProvider.CreateZoneDelegationForExternalDNS(gslb)
• controller tests

[ytsarev]

Refactoring details were presented to the team and the test k8gb build was e2e tested. All good, amazing job @kuritka !