Custom domain access issues and unhealthy instances

Question

Last evening, an email was received from a customer reporting that they cannot access the site. This morning, it was discovered that the site is inaccessible with custom domains. Health checks indicate that the instances are "unhealthy," and restarting them has not resolved the issue.

Answer 1

What is the error you are seeing when browsing the website? instead of restart, perform a stop and start and monitor the instances. Do you have app insights configured with the app service? if so, go and run this query

traces 
| where timestamp > ago(24h)
| summarize count() by roleInstance

We should understand if the role instances are changing frequently, or do they remain same? The period of Evalution can differ. I just provided an example.

I faced a similar issue and there can be multiple reasons why that happens? Curious, how many instances do you have? Is this the first time this has happened?

if this .net/windows, you can enable debug trace level to dump out all the traces to understand if your worker is crashing.