Lego: How to serialize dns solver requests

[KnicKnic]

I am using lego through traefik. The provider I am using is DuckDns.
There is a imitation with duckdns that it only has one txt record per account, that txt record will be presented for any lookup request on any subdomain.

So test1.test.duckdns.org and test2.test.duckdns.org do not have different txt records. Currently I want to be able to request in traefik

 [[acme.domains]]
   main = "test1.test.duckdns.org"
   sans = "[test2.test.duckdns.org"]

I was wondering how I could serialize the requests such that the two requests do not overlap and that test1 is validated and then test2 is validated (currently test2 will succeed and then eventually test1 will get retried). I am okay with all requests going through DuckDNS are serialized, but if possible it would be nice to limit it only to one per account. I am curious to this interaction across the operation that spans both Present and CleanUp.

@ldez - due to already paging in context on https://github.com/xenolf/lego/pull/676

Thanks!

[ldez]

I saw the problem with DuckDNS yesterday, and I may have a solution.
For the moment, I have to think about it.

[ldez]

Closed by #700