Knowledge Base

Plesk and websites are down with 503 Service Unavailable: Configuration file is not well-formed XML

Symptoms

Plesk and websites are inaccessible:
```
Error 503: Service Unavailable
```

In the Event Viewer the following error message can be found:

The worker process for application pool 'plesk(default)(2.0)(pool)' encountered an error 'Configuration file is not well-formed XML
' trying to read configuration data from file '\?C:inetpub  empapppoolsplesk(default)(2.0)(pool)plesk(default)(2.0)(pool).config', line number '2'.  The data field contains the error code.

Plesk pool stops after the start.

A restart of IIS crashes:

Attempting stop...
Internet services successfully stopped
Attempting start...
Restart attempt failed.
The IIS Admin Service or the World Wide Web Publishing Service, or a service dependent on them failed to start.  The service, or dependent services, may had an
error during its startup or may be disabled.

WAS fails to start. All sites and pools are stopped.

The file C:WindowsSystem32inetsrvconfigapplicationHost.config has a large file size.

Cause

There is a feature in IIS 8.5 called Dynamic Website Activation.

This feature has dynamicRegistrationThreshold restriction which has a value of 100 by default.

For unknown reasons, this IIS feature is not activated in most cases.

However, sometimes it becomes activated and in case if there are a lot of websites on the server (100 or greater, by default), the service will not activate any of the sites when the service is started.

Resolution

Set the value of dynamicRegistrationThreshold to the new threshold value, e.g. 10000 as follows:

Open IIS Manager.
Select the server in the Connections panel , and then double-click Configuration Editor .
Select the section system.applicationHost/webLimits .
Set the value of dynamicRegistrationThreshold to the new threshold value for example 2000.
Start IIS service:
```
iisreset /start
```