If you are preparing to upgrade to Tableau Server 9.0 and have a distributed Tableau Server environment that has a firewall between the servers, be aware that there is a missing port requirement in the Administrator's Guide (http://onlinehelp.tableau.com/current/server/en-us/help.htm#ports.htm). After a couple of long troubleshooting sessions, I discovered that port 8600 needs to be open for the "vizportal" process. I opened a case and this morning Tableau Support confirmed the error in the documentation and they will update ASAP.
In the meantime, if you have "spare" ports that are open but not being used, you can change the default port by running "tabadmin set worker0.vizportal.port 9999" (replace 9999 with the port you want to change to). If you have additional workers, you may have to run that command for each one ("tabadmin set worker1.vizportal.port 9999", "tabadmin set worker2.vizportal.port 9999", etc.). Once you are done, remember to "tabadmin configure" and "tabadmin restart" to make the new port stick.