is there a limit on the number of domains for a SAN?
a friend of mine who is in the beta experienced some issues creating a SAN with 4 domains, but when he put the rest again in another cert it weirdly worked for him...
The current limit is no more than 100 names in a SAN.
okay nice to know maybe the issue lied in the fact that he essentially tried to request a domian in the format like www.ssl.example.com which has not just 3 bur 4 parts, no Idea, I'll see on gen availability
Does that limit of 100 subject alternate names still exist?
Yes, it's listed here: https://community.letsencrypt.org/t/rate-limits-for-lets-encrypt/6769
Has there been thought given to making this rate limit queryable via ACME?
There has been some discussion on adding a rate limit endpoint (or headers, i.e. X-Certificates-Remaining: 5 for new-cert, etc.) Nothing that's being worked on at the moment, though. Here's a relevant issue: