AZFD0005: External startup exception

This event occurs when an external startup class throws an exception during function app initialization.

Event ID AZFD0005
Severity Error

Event description

An external startup class is a class registered with the FunctionsStartupAttribute. It is often used to register services or configuration sources for dependency injection. For more information on the feature, see use dependency injection in .NET Azure Functions.

If a call to either of the Configure() methods on the FunctionsStartup class throws an exception, it will cause the function app initialization to fail. The functions host will catch this exception, log the error, and retry initialization. This retry helps to recover from transient errors, but permanent errors may be logged many times as the host retries.

If APPLICATIONINSIGHTS_CONNECTION_STRING is set as an app setting, the error will also be logged as an exception in Application Insights.

How to resolve the event

Every occurrence of this event is unique to the application. Investigate the error message and stack trace to see what may need to be done to prevent this error in the future. For example, a timeout may need to be retried; or an error calling an external service may need to be handled.

When to suppress the event

This event shouldn't be suppressed.