I have installed IEM 9.5.4 on a second server for DR and everything installed fine but I am getting error 503 on all the plugins when I run the Diagnostic, as well as an error saying the server can not reach the internet. I can browse the net just fine and http://sync.bigfix.com resolves fine. See image.
It’s been a while since I installed a fresh DSA, but I seem to recall some of the HTTP services may not respond until the initial sync is complete. Check the FillDBData\FillDB.log on each server to see whether replication is occurring. Using the SQL Profiler on one or both DSAs, or capturing network traffic on the SQL port (default tcp:1433 for Microsoft SQL) to see if the DSA servers are communicating with each other. This might resolve itself when the initial sync is complete.