HTTP 503 Service Unavailable when hosting CData Arc in IIS, but the same port works for the embedded webserver

  • 19 December 2023
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When attempting to host CData Arc in IIS, the service does not start successfully. IIS does not appear to report any issues when starting the service, but when you attempt to reach the site, you will see an HTTP 503 Service Unavailable: 



Cause: This can happen if you select a port in IIS that you have previously used with the embedded webserver provided with CData Arc – a common example being port 8001, but this can happen for any port you have selected for the embedded webserver:  



The embedded web server provided with CData Arc will reserve any ports that you bind against so that any other process that attempts to bind on that port will not be able to make that reservation. 


To confirm the issue is caused by a port reservation:  


Open a command prompt and run the following command: 

netsh http show urlacl 

 This will list all of the reserved entries on the machine. If the URL that you are trying to bind shows up like this: 

     Reserved URL            : http://+:8001/ 



Resolution: You can use another netsh command to remove the reservation (just use the same value from the listing) : 


netsh http delete urlacl http://+:8001/ 

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