Major Description
With an ssl_multicert.config of
ATS will start up without any (as far as I could tell) errors, even when the cert chain file is completely missing. It just silently accepts the config, and brings ATS up in a poor state as far as TLS is concerned.
IMO, we should at a minimum write some very serious warnings and errors on this, but maybe even refuse to startup (or reload) the config if the cert chain file is missing. This is serious enough that the server is in a non-functional state if it happens.