The Dynatrace site extension registers IIS modules at installation time. If registration is complete but the actual IIS module files aren't in place (or corrupt), the App Service might return a 503 Service Unavailable message. Also, the Kudu AppPool will no longer be available, which effectively means that you can no longer fix your app. If this occurs, please file a support case.
Fortunately, there's a way to recover from such a situation by adding the following setting in Application Settings to effectively deactivate all site extensions:
WEBSITE_PRIVATE_EXTENSIONS=0
This setting will give you access to Kudu once again. After that, reinstall the site extension and set WEBSITE_PRIVATE_EXTENSIONS=1 (or remove the setting entirely). Following application restart, everything should work again, including Dynatrace monitoring.
