Users report certificate warnings or cannot reach the App Service API through the custom domain. How would you debug it?

Debug a TLS certificate or domain binding incident in App Service

Investigate production failures caused by custom domain, DNS, TLS certificate, or HTTPS binding problems.

1Say itAnswer out loud first

2CompareCompare with Core answer

3RefineRefine with Stronger and Advanced

TL;DR

I would check whether the problem is DNS resolution, App Service custom domain binding, TLS certificate validity, certificate binding, HTTPS-only behavior, or a proxy in front of App Service. I would test from outside the corporate network and inspect the certificate presented to the client, including hostname and expiration. If only some users are affected, I would consider DNS propagation, caching, regional routing, or a CDN/front-door layer. I would communicate clearly because certificate and domain incidents look severe to users.

Full answer below

Practice focus

DNS, custom domain bindings, TLS certificates, HTTPS enforcement, proxy boundaries, and communication during edge incidents.

Answer first

Answer path

Core answer first, then checkpoints toward a stronger answer.

Start
Core answer
Start here. This is the direct spoken answer to practice first.
Why this question matters
Edge incidents are visible and urgent because users cannot even reach the application path. This question tests basic but important production boundary thinking.
I would check whether the problem is DNS resolution, App Service custom domain binding, TLS certificate validity, certificate binding, HTTPS-only behavior, or a proxy in front of App Service. I would test from outside the corporate network and inspect the certificate presented to the client, including hostname and expiration. If only some users are affected, I would consider DNS propagation, caching, regional routing, or a CDN/front-door layer. I would communicate clearly because certificate and domain incidents look severe to users.
Checkpoint
Stronger answer
Optional upgrade with examples, trade-offs, and sharper phrasing.
I would compare the public path with the App Service configuration. The custom domain needs to point to the intended app, the app needs a matching binding, and the certificate needs to cover the hostname being used. If a gateway, Front Door, or CDN terminates TLS before App Service, I would identify where the bad certificate is presented and where redirects are generated. I would also verify that app-generated links, auth callbacks, and CORS settings use the public domain after the edge fix.

Review signals

Use these to catch weak phrasing, shallow reasoning, and risky claims.

Common mistakesCandidateCommon mistakesMistakes that weaken the answer or signal shallow understanding.Open details

Details

Checking only the Azure default hostname.
Ignoring where TLS terminates when a proxy is involved.
Forgetting auth callbacks and generated links after domain changes.
Not monitoring certificate expiration.

Users report certificate warnings or cannot reach the App Service API through the custom domain. How would you debug it?

Practice focus

Answer path

Why this question matters

Review signals

Follow-up prompts

Continue practice

Tech stacks

Skill areas

Was this drill useful?

Found this answer useful?

Human editorial direction

Users report certificate warnings or cannot reach the App Service API through the custom domain. How would you debug it?

Practice focus

Answer path

Why this question matters

Review signals

Follow-up prompts

Continue practice

Tech stacks

Skill areas

Start a conversation

Was this drill useful?

Found this answer useful?

Human editorial direction