I ran into a new error today during a WSUS synchronization for SCCM Software Updates. Synchronizations had been running fine for a while, but it would fail after running for an extended amount of time. The error was easy to find in the wsnycmgr.log file in the Configuration Manager logs:
Usually when synchronization fails, it does so immediately due to WSUS not being configured properly, WSUS missing a hotfix, or not being mapped to the proper ports in IIS.
After a bit of research, I found a very useful article saying that the WSUS Application Pool in IIS may be running out of memory during synchronization. To help identify this issue, you will see the 503 error in wsyncmgr.log, and the Application pool for WSUS will be stopped in IIS when it fails:
To fix the issue, you can set the Private Memory Limit to 4000000 or 8000000 as recommended in the article and restart the application pool. You can then trigger a manual synchronization and monitor the log again.
So far in testing this change in other environments, it appears that it can significantly improve performance and cut down on those sync times as well.