Lync mobility does not work externally HttpStatus="500", HttpReason="Internal Server Error"

Error

Lync mobility does not work externally when configured on windows 2012 with "IIS 8.0, ARR & Lync 2013", Internally it works fine. In logs we receive following:
HttpStatus="500", HttpReason="Internal Server Error"

Cause

External users goes to port 443, it does not work and fails with "Internal Server Error".For Lync 2013 external request should go to port 4443.
Although we provided httpsPort - 4443 & httpPort - 8080 while creating server farm, but due to some reason it was not getting reflected in the applicationHost.config file and was causing issue.

Resolution

To browse Lync from the external URL it must hit the 4443 & 8080 port, it does not work over port 443 & port 80.
Note: We have mentioned port 4443 & port 8080 while creating server farm but that did not added in the applicaitonhost.config file. seems like a bug.
Manually added httpsPort="4443" httpPort="8080" in the applicaitonRequestRouting tag of the applicationHost.config file for the server farm.

<webFarm name="lyncfe.domain.com" enabled="true">
            <server address="lyncfe.domain.com" enabled="true" >
                     <applicationRequestRouting httpsPort="4443" httpPort="8080" >
                              <protocol timeout="00:03:20" />
                      </applicationRequestRouting>
            </server>
 </webFarm>

Ref: http://blogs.technet.com/b/nexthop/archive/2012/04/25/lync-server-2010-mobility-deep-dive-autodiscover-service.aspx