problems with multiple IP adresses for SP? Aliases?

[Peter Schober]

* Dr. Marco Lechner <mlechner at bfs.de> [2017-04-11 10:14]:
> 2. Is it possible (any hint to the Wiki or Doku) to use ServerAlias
> names for the SP? Well, our application shold be available using
> different URLs/Servernames (foo.bfs.de as well as bar.bfs.de ...) -
> anybody who can point me to a configuration example. shibboleth2.xml has
> onl one entityID entry). Will SSO still work when changing from one
> Servernam eto the other?

Not sure about your first question, but regarding the second one above:
The IDP needs accurate metadata for every FQDN/vhost on every SP. If
anything you do to the SP's web server configuiration changes the URL
the browser sees for the resource, that usually requires
modified/amended metadata at the IDP to match those FQDNs.
(In fact this may also answer your first question.)

The one alternative to that is signing authentication requests from
the SP, and configuring the IDP to rely on signed requests alone,
skipping the verification of locations to send reponses to using SAML
metadata.
Since this requires changes to both the SP and the IDP this usually
only works within closed groups of SPs and IDPs, or even only within
the same organization. E.g. for mass-hosting dozens (or thousands) of
vhosts on the same system relying on signed requests is an easier
alternative than coming up with the tooling to create and maintain
matching SAML metadata at the IDP for every change at the SP.
-peter