Issue
When trying to connect to a station running on a UNC an intermittent error appears:
"Cannot Open station. Service Unavailable (503)".
Environment
Niagara UNC
Cause
This error indicates that the embedded UNC's web server is currently unable to handle the request due to a temporary overloading or maintenance of the server. In this case, it means that the web server is refusing the connection due to a thread overloading condition. More specifically, the UNC is out of web service threads.
Resolution
Starting in Niagara build 431, a line item was added to the system.properties file that sets the maximum thread pool size for the web services. Using the admin tool open the UNC's system.properties file. From the drop-down menu, select Admin Tool > Host > Edit File > System Properties. Locate the line that defines the webServer.threadPoolSize. Increase the webServer.threadPoolSize from the default value of 15 to 30. Save the changes to the file and re-boot the UNC to initialize the new thread pool size.
