SqlAGReplica: Add round-robin read only routing lists

[codykonior]

Details of the scenario you tried and the problem that is occurring

The SqlAGReplica resource accepts a ReadOnlyRoutingList of type [string[]]. On the SMO side this has a matching ReadOnlyRoutingList property of type StringCollection as that's how these lists were defined for SQL Server 2012 and 2014, and as of the latest patches should all be functional.

In SQL 2016 there's an additional SMO property LoadBalancedReadOnlyRoutingList of type System.Collections.Generic.IList<System.Collections.Generic.IList> and an associated read-only property of LoadBalancedReadOnlyRoutingListDisplayString. This is intended to allow the passing of server groups as follows:

READ_ONLY_ROUTING_LIST = (('Server1','Server2'), ('Server3', 'Server4', 'Server5'), 'Server6')

The question is how the DSC resource should be modified to support this:

• You could change the type specification on ReadOnlyRoutingList from [string[]] to [object[]] to allow the possibility of passing in either a string array, or array of strings/arrays. The code would then decide if it's SQL 2016 and if so use LoadBalancedReadOnlyRoutingList and LoadBalancedReadOnlyRoutingListDisplayString for comparisons (it will be valid for both the old style list and the new style list). If SQL 2012/2014 are detected then ReadOnlyRoutingList and the current string matching will be used (as the newer property would throw an error). I think this is the easiest way to handle it but would it be classified as a breaking change? It doesn't actually break anything...
• Alternately you could add an additional LoadBalancedReadOnlyRoutingList property. I think this is harder for users to use. I also don't know if there are DSC helper tools to add and fix references in all the files or if it all has to be copy-pasted from another property manually.

[codykonior]

@mdaniou

[codykonior]

Another option: we keep the string array, and if server names are passed in they will be used as normal.

If any single entry has parenthesis then each array entry will be parsed into their own groups.

‘Server1’, ‘Server2’ = Use the old style.

‘Server1’, ‘Server2’, ‘(Server3, Server4)’ = Use grouping style.