AirBrake is a great way to track errors and exceptions in your AppHarbor hosted application.
To log errors to AirBrake, you use the AirBrake API directly or you can use SharpBrake. If you want to use SharpBrake, there's a Nuget package available. SharpBrake has a HttpModule that works with ASP.NET Webforms applications and an extension method that will easily let you log exceptions to AirBrake.
You Airbrake API key will be available in your
web.config like this:
<add key="HOPTOAD_API_KEY" value="key"/>
For compatibility with SharpBrake, AppHarbor also inserts the following:
<add key="Airbrake.ApiKey" value="key"/>