I have an application that can throw an InvalidOperationException during the startup process before the host has been created. What I would like to do is capture this error, and handle it by displaying a static, custom error page (i.e. ErrorPage.html)
Is this possible? Everywhere I seem to look makes it seem as though this is an impossible task and that the default 500.30 - ASP.NET Core app failed to start is the only page that will appear in a situation where the host fails to establish by the time the exception is thrown.
One option to achieve a custom error page on host errors generating 500 responses would be to use some gateway or proxy in front of your app. The idea would be to handle certain responses by showing some error content from the gateway.
Options would include custom error pages in Azure Application Gateway or a middleware handler if using a YARP proxy instance.