Azure custom 404 page - html

Question

I have created a web application using Microsoft Azure and uploaded static html pages to the web application.
It works fine, however, I would like to set a custom 404 page. Where or how can I do this using the Azure portal ?
Just to be clear, this is not a visual studio project, it's just some static html files. I just want to tell azure to use my 404 page instead of the default text it displays when a page cannot be found.
EDIT
Please note, this has nothing to do with IIS. I dont even have a web.config file. I am simply hosting some static html files in Azure and want a custom 404 page. I have already made the 404.html page.

Answer 1

Seems like you have to add a web.config file in your root directory. This seems like a workaround, but doing that and adding the following code works:
<?xml version="1.0" encoding="UTF-8"?>
<configuration>
<system.webServer>
<httpErrors errorMode="Custom" defaultResponseMode="ExecuteURL">
<remove statusCode="404" subStatusCode="-1" />
<error statusCode="404" path="/404.asp" responseMode="ExecuteURL" />
</httpErrors>
</system.webServer>
</configuration>

Answer 2

Follow these steps to configure a custom 404 page for a Azure Static Web App:
Create a file named staticwebapp.config.json in root page (same folder as starting page i.e. index.html)
put these lines inside it:
{
"responseOverrides": {
"404": {
"rewrite": "/404.html"
}
}
}
Put your custom 404 page in root or subfolder (in this example 404.html is in root folder)

Answer 3

After a lot of testing and research, it was found that using responseMode="ExecuteURL" would result in a correct redirect, but the browser would report 200 Status rather than a 404. To fix this we removed the "/" and changed to responseMode="File" based on insight from this post: web.config errors fail with responseMode="File"
We are just hosting a simple static HTML site, not a web app, and this code worked:
<?xml version="1.0" encoding="UTF-8"?>
<configuration>
<system.web>
<customErrors defaultRedirect="404.html" mode="RemoteOnly">
<error statusCode="404" redirect="404.html" />
<error statusCode="500" redirect="500.html" />
</customErrors>
</system.web>
<system.webServer>
<httpErrors existingResponse="Replace" defaultResponseMode="File" errorMode="Custom">
<remove statusCode="404" />
<error statusCode="404" path="404.html" responseMode="File" />
<remove statusCode="500" />
<error statusCode="500" path="500.html" responseMode="File" />
</httpErrors>
</system.webServer>
</configuration>