feat: add flag --source-dns-suffix

[bewing]

Add a flag indicating the cluster DNS suffix for the source cluster. If present, lbsvc strat should use the fully qualified DNS name for a ClusterIP service instead of a LoadBalancer service. This allows transfers between bare-metal clusters where Service IPs are reachable between clusters (Calico BGP to ToR switch, etc).

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• I have read the CONTRIBUTING document.
• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added tests to cover my changes.
• All new and existing tests passed.

[bewing]

Open to feedback if this is even worth merging. At a glance, might possibly be a solution to #175 as well. Might be worthwhile to make it more generic and just use ServiceIPs as reported by the clusters instead?

[utkuozdemir]

Hi,

Thank you for the PR. I'll have a look into this when I have some time. But from the first look to it, it looks like a very specific use case and probably not something that the tool should support explicitly.

Additionally, the strategy lbsvc should use LoadBalancer type services exclusively, not conditionally. Otherwise it contradicts its name and becomes unintuitive.

Did you check if what you need is achievable by passing some custom Helm values? It might address your use case.