The MinIO server for backups has special requirements for HTTPS. I want
to use subdomains for bucket names, so the certificate must have a
wildcard name, which requires using the DNS-01 challenge. Fortunately,
it is actually pretty easy to use `nsupdate` with GSS-TSIG
authentication to automate DNS record creation, and by default, all
domain-member machines can create any records. Thus, using the `manual`
auth plugin for `certbot` and a script to run `nsupdate`, obtaining the
wildcard certificate is fairly straightforward.
The biggest issue I encountered while developing this feature was
caching of NXDOMAIN responses. There doesn't seem to be a way to change
the TTL of the SOA record of the Active Directory DNS domain, which
defaults to 3600, meaning NXDOMAIN responses are always cached for an
hour. When adding a record using `nsupdate -g`, the tool always
performs a SOA lookup of new name to find the target zone for it. Since
the name does not exist yet, the domain controller responds with
NXDOMAIN, which gets cached by the main DNS server. Thus, even after
adding the record, the ACME server will not be able to resolve the
name for up to an hour. We can a void this by explicitly setting the
target zone. That would not work in a multi-domain forest, but
fortunately, we do not have to worry about that.
This role borrows some logic from the *postgresql-cert* role.
Eventually, I probably want to combine some of the steps from both of
these roles, possibly replacing the old *certbot* role.
Dustin