[jcgl]

Afaiu, that's only a problem for trying to _delegate_ to multiple clients. But routine operation with multiple clients works just fine in my experience (doing multi-region load balancing). Multiple TXT records are created, I think (speaking off the top of my head).

[cpach]

Ah! I stand corrected.

[jcgl]

I wanted to quickly double-check my (albeit limited) experience against docs. The RFC[0] implies the possibility of what I described (provided a well-behaved ACME client that doesn't clobber other TXT records):

   2.  Query for TXT records for the validation domain name
   
   3.  Verify that the contents of one of the TXT records match the
       digest value

And then the certbot docs[2] show how it's a well-behaved client that wouldn't clobber TXT records from concurrent instances:

> You can have multiple TXT records in place for the same name. For instance, this might happen if you are validating a challenge for a wildcard and a non-wildcard certificate at the same time. However, you should make sure to clean up old TXT records, because if the response size gets too big Let’s Encrypt will start rejecting it. > ... > It works well even if you have multiple web servers.

That bit about "multiple webservers" is a little ambiguous, but I think the preceding line indicates clearly enough how everything is supposed to work.

[0] https://datatracker.ietf.org/doc/html/rfc8555#section-8.4

[1] https://letsencrypt.org/docs/challenge-types/#dns-01-challen...