Hello Alexander,

There are a few things to consider before deciding how you'd like to set
this up.

The first question, I think, is: why do you want to run two puppetdb
services rather than just pointing both puppet masters to a single puppetdb
service?  If you're goal is to share the postgres database, then in most
cases, that will be your bottleneck (as opposed to the puppetdb service
itself).  Thus, you might not be buying yourself much by adding a second
puppetdb service.

Second: do you have a shared CA for the two puppet masters?  Since the
puppetdb service's SSL auth will be based on a single puppet master's CA,
you won't be able to connect to a single puppetdb service with two
different masters using two different CA's.

Third: If you do decide to run two puppetdb services pointing to a single
postgres instance--this *should* work, but it's not necessarily a
recommended configuration.  You'd need to be very careful to make sure that
the two puppetdb services were always running the *exact* same version as
one another; if you were ever to upgrade one of them without upgrading the
other, you might trigger a schema migration in the postgres database that
would render it incompatible with the older version of puppetdb.

Please let us know if you have any additional questions!
Thanks
Chris