Why does my Azure Web App with a custom domain 404 intermittently when not used? (No logs, TLS/SSL)

Mark Infante 0

I have just recently started running my frontend web application full time. It is an 'always on' application with a custom domain and SSL/TLS.

Often times when I try to hit the custom domain, the website will give the usual unsecure messaging for plain http connections, where you have to jump through some hoops ("this is unsafe") in order to reach the landing page. Then, when bypassing it will bring me to the Azure web app default 404 page.

If I restart the app, flush my dns, and wait 10 minutes, usually this problem will go away. If I repeatedly try to hit the application while flushing my dns and clearing cache, eventually I can get in. I'm wondering why my application "goes down" when not used, why I cannot track this behavior, and why 'always on' and health tracking does not help.

Has anyone experienced this? I've heard whisperings online that I may have to set up a job to hit the frontend every 10 minutes from now until eternity. I'm not sure if that solution is related but I thought I'd mention it anyway.

Silvia Wibowo 3,011 Reputation points Microsoft Employee

2024-04-25T23:49:31.8633333+00:00

What App Service Plan do you use?

Did you set TLS/SSL Settings - HTTPS Only = On?
Mark Infante 0 Reputation points

2024-04-26T13:22:11.1033333+00:00

@Silvia Wibowo We use HTTPS Only = On. The App Service Plan is a Linux Plan with 3 apps, pretty consistently using about 75/80% of memory. We're using it pretty much out of the box right now in terms of customization.
Silvia Wibowo 3,011 Reputation points Microsoft Employee

2024-04-28T23:45:40.1733333+00:00

You mentioned that your App Service Plan is Linux OS with 3 apps. What pricing tier (Free, Shared, Basic, Standard, Premium, PremiumV2, PremiumV3, Isolated, IsolatedV2)?

Note: In Basic and Standard service plans, you can turn on the Always On setting to keep the app always loaded.
SnehaAgrawal-MSFT 18,366 Reputation points

2024-04-29T09:59:34.47+00:00
@Mark Infante Thanks for asking question! If you receive an HTTP 404 (Not Found) error when you browse to the URL of your custom domain, the two most-likely causes are:

The browser client has cached the old IP address of your domain. Clear the cache, and test DNS resolution again. On a Windows machine, you clear the cache with ipconfig /flushdns.

You configured an IP-based certificate binding, and the app's IP address has changed because of it. Its suggested to Remap the A record in your DNS entries to the new IP address.

Let us know.