ConfigMgr 2012 R2 – WSUS sync fails with HTTP 503 errors

Ran into this issue with ConfigMgr 2012 R2 where it was unable to synchronize Software Update Point with the WSUS server. A review of the component status messages for the SMS_WSUS_SYNC_MANAGER component on the primary site server reveals errors related to WSUS synchronization which are similar to the following:
[su_note note_color=”#efacad”]Message ID: 6703 WSUS Synchronization failed. Message: The request failed with HTTP status 503: Service Unavailable. Source: Microsoft.UpdateServices.Administration.AdminProxy.CreateUpdateServer. [/su_note]
Got the following error when trying to open Update Services on the WSUS server

[su_note note_color=”#efacad”]Error: Connection Error An error occurred trying to connect to the WSUS server. This error can happen for a number of reasons. Please contact your network administrator if the problem persists. Click the Reset Server Node to connect to the server again. [/su_note]

In addition to the above, attempts to access the URL for the WSUS Administration website (i.e., http://CMCASSERVER:8530) fails with the error:

[su_note note_color=”#efacad”]HTTP Error 503. The service is unavailable[/su_note]

In this situation, the most likely cause is that the WsusPool Application Pool in IIS is in a stopped state, as shown below.

Also, the Private Memory Limit (KB) for the Application Pool is probably set to the default value of 1843200 KB.

If you encounter this problem, increase the Private Memory Limit to 4GB (4000000 KB) and restart the Application Pool. To increase the Private Memory Limit, select the WsusPool Application Pool and click Advanced Settings under Edit Application Pool. Then set the Private Memory Limit to 4GB (4000000 KB).

After the Application Pool has been restarted, monitor the SMS_WSUS_SYNC_MANAGER component status, wcm.log and wsyncmgr.log for failures. Please note that it may be necessary to increase the Private Memory Limit to 8GB (8000000 KB) or higher depending on the environment.

Now WSUS is back online!