HTTP Error 503 The service is unavailable – How to resolve this website error in Odin Plesk Windows servers
In Odin Plesk Windows servers, customers sometimes report their sites being unavailable with the error showing : “HTTP Error 503. The service is unavailable.” This usually happens after a major change like a migration, site restore, etc., and leads to all sites of the user being unavailable.
What is this error?
As a rule of thumb, this error usually happens when the IIS configuration settings are somehow corrupted by a recent change. It could be wrong user profile settings, wrong profile settings, or even an issue with the configuration files.
How to resolve this error?
Start by checking if the relevant application pool is enabled. If it is, then check the Event Viewer for specific causes. More information could also be found in http.sys logs. Once you locate the root cause, fix it (configuration update, DLL file path fix, etc.), and then restart the application pool.
Or, if you know no other sites are affected, restoring the old IIS configuration settings would resolve this error in a jiffy.