Application Initialization for an App Service in Azure not working - azure

Question

We have an appservice in Azure configured to have max 8 instances and everytime we deploy, we see restart activity under Availability and Performance (Diagnostics).
We have also observed loads of 5xx errors this is happening. Our analysis so far is that requests are getting routed to cold instances which have just been spun up and these are reasons for getting failures.
I have found this guide -> https://azure.github.io/AppService/2020/05/15/Robust-Apps-for-the-cloud.html and following the Application Initialization advice.
As a result, I have added
<applicationInitialization >
<add initializationPage="/healthcheck"/>
</applicationInitialization>
to web.config
I restarted the app service and sent few test requests to the app. In the Application Insights I can see the health endpoint being called - so application initialization logic is kicking in. However, it is calling http://localhost/healthcheck and 307 being returned.
I looked into 307 and the reason, it is returning 307 as app service is configured to only run using https protocol but http://localhost is non-https and hence service is redirecting.
What do i do need to so it calls the app service with https protocol.
I tried adding the full app url in the application initialization block but then I can see
http://localhost/https://app-service-name.azurewebsites.net/healthcheck being called - which is even worse.
What am I doing wrong?

Answer 1

I assume your application runs ASP.NET Core. As mentioned in the other answer, application initialization only supports HTTP, so you need to make that work. What we did is this:
/// </summary>
public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
{
// ...
// IIS App initialization requires HTTP
app.UseWhen(
context => !WarmupController.IsWarmupRoute(context.Request.Path),
mainApp => mainApp.UseHttpsRedirection()
);
WarmupController.IsWarmupRoute basically only contains a StartsWith check.
This way you allow HTTP requests only for your warmup/healthcheck route. There is no need to adapt web.config or AppService settings.