I had this issue before https://technology.wayneschoolswv.org/2015/03/30/wsus-synchronization-in-configmgr-2012r2-fails-with-http-503-wsus-pool-stopped/ and the solution that worked then works still with just a small change. Who knows what changed but after a Patch Tuesday in early March 2017 I started getting 503 errors in my IIS logs when my machines were checking in with our WSUS server to get updates.
What is really strange is that this happened in March the last time presumably after Windows installed updates! 🙂
You will see errors in various places such as the component status messages for the SMS_WSUS_SYNC_MANAGER component on the primary site server reveals errors related to WSUS synchronization which look like the following:
Message ID: 6703
WSUS Synchronization failed.
Message: The request failed with HTTP status 503: Service Unavailable.
If you try to access the URL for the WSUS Administration website (i.e., http://wcboe-sccm.wcs.local:8530) it fails with the error:
HTTP Error 503. The service is unavailable
The problem last time and this time is that the WsusPool Application Pool in IIS is in a stopped state, as we can see below.
The last time we had this issue we increased the Private Memory Limit (KB) for the Application Pool from the default value of 1843200 KB to 4000000 KB. You access this by loading IIS Manager, clicking on Application Pools in the left windows, click on WsusPool in the middle window to highlight it, then clicking on Advanced Settings in the right window under Edit Application Pool.
This time it was the same issue, but the 4GB limit we set last time was being exceeded so I just increased the limit to 8GB and restarted the Application Pool. This assumes that you have enough memory in your server to allow this process to use this much memory.
After the Application Pool has been restarted, monitor the SMS_WSUS_SYNC_MANAGER component status, wcm.log and wsyncmgr.log for failures. You can also set this setting to 0 (zero) which will allow the WsusPool to use as much memory as it needs.
You can watch and see if your IIS is exceeding the amount of memory you have set for it by loading Task Manager and watching the IIS Worker Process. As seen below mine was stopping because this process was now using more than the 4GB I had set last time.
WSUS Logs with error info.
You can see this issue in the WCM.log from the primary site server. It will contain numerous entries similar to the following:
The request failed with HTTP status 503: Service Unavailable or Remote configuration failed on WSUS Server.
The wsyncmgr.log from the primary site server will show errors similar to the ones below:
Sync failed: The request failed with HTTP status 503: Service Unavailable or The request failed with HTTP status 503: Service Unavailable.