A .NET API works locally but fails in App Service with startup errors after deployment. The suspected cause is runtime mismatch. How would you handle it?

Debug a .NET runtime mismatch in Azure App Service

Identify a failed App Service deployment caused by a mismatched .NET runtime or publish target.

1Say itAnswer out loud first

2CompareCompare with Core answer

3RefineRefine with Stronger and Advanced

TL;DR

I would confirm the .NET target framework and publish mode of the artifact, then compare it with the App Service stack or container image. A framework-dependent deployment needs the expected runtime available on the host. A self-contained deployment carries more runtime with it but still needs correct startup configuration. I would check startup logs and deployment output because they usually point to missing runtime, wrong executable, or incompatible hosting configuration.

Full answer below

Practice focus

Runtime checks, framework-dependent versus self-contained publish, App Service stack settings, and release validation.

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
A framework-dependent artifact, self-contained publish, container image, and App Service runtime each carry different hosting assumptions. Startup logs and artifact metadata reveal when the deployed output and host contract do not match.
I would confirm the .NET target framework and publish mode of the artifact, then compare it with the App Service stack or container image. A framework-dependent deployment needs the expected runtime available on the host. A self-contained deployment carries more runtime with it but still needs correct startup configuration. I would check startup logs and deployment output because they usually point to missing runtime, wrong executable, or incompatible hosting configuration.
Checkpoint
Stronger answer
Optional upgrade with examples, trade-offs, and sharper phrasing.
I would fix the release process rather than patching one app manually. The pipeline can print the SDK version, target framework, publish mode, artifact contents, and App Service runtime setting before deployment. If the team uses Linux App Service, I would verify startup command, case-sensitive paths, file permissions, and environment-specific behavior. If the team uses containers, I would inspect the image tag and base image instead of the App Service stack alone.

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

Only testing locally with a different SDK/runtime than production.
Changing the portal stack manually without updating infrastructure definition.
Confusing SDK version with runtime version.
Ignoring Linux path and startup command differences.

A .NET API works locally but fails in App Service with startup errors after deployment. The suspected cause is runtime mismatch. How would you handle it?

Practice focus

Answer path

Why this question matters

Review signals

Follow-up prompts

Continue the section

Technologies

Tech stacks

Skill areas

Was this drill useful?

Found this answer useful?

Human editorial direction

A .NET API works locally but fails in App Service with startup errors after deployment. The suspected cause is runtime mismatch. How would you handle it?

Practice focus

Answer path

Why this question matters

Review signals

Follow-up prompts

Continue the section

Technologies

Tech stacks

Skill areas

Start a conversation

Was this drill useful?

Found this answer useful?

Human editorial direction