Question 635 of 823
AZ-400 Practice Question: Design and implement build and release pipelines
A team uses Azure Pipelines to build a .NET Core application. The build pipeline runs successfully, but the release pipeline fails when deploying to Azure App Service with the error: 'ERROR_FILE_IN_USE'. What is the most likely cause?
⚠ Common exam trap
Test-takers frequently confuse 'ERROR_FILE_IN_USE' with a slot configuration or scaling issue, but the root cause is always the running process holding file locks, which is directly resolved by the 'Take App Offline' setting in the deployment task.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The 'Take App Offline' setting is not enabled in the deployment task.
The 'ERROR_FILE_IN_USE' error occurs when the deployment process tries to overwrite files that are currently locked by the running application. Enabling the 'Take App Offline' setting in the Azure App Service deploy task places an app_offline.htm file in the wwwroot directory, which gracefully shuts down the application and releases all file locks before the new binaries are copied. Without this setting, the running process holds locks on the DLLs, causing the deployment to fail.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
The deployment slot is not configured correctly.
Why it's wrong here
Incorrectly configured deployment slots cause swap or routing failures, but they do not place locks on the deployed application’s files. File lock errors arise from the running process holding binaries, which is unrelated to slot settings.
- ✓
The 'Take App Offline' setting is not enabled in the deployment task.
Why this is correct
The 'Take App Offline' setting instructs the Web App to place an app_offline.htm file in the site root, which gracefully shuts down the app and releases any locks on its assemblies and files. Without this, the running process holds the DLLs, causing 'file in use' errors when the pipeline tries to overwrite them.
- ✗
The Azure App Service plan is not scaled appropriately.
Why it's wrong here
Scaling the App Service plan changes the number or size of instances, which affects performance and capacity but has no effect on file locking. File locks are a per-instance operating system artifact, so adding more resources won't release locks held by the current worker process.
- ✗
The build configuration is set to Release instead of Debug.
Why it's wrong here
The build configuration (Release vs Debug) changes compiler optimizations and symbol/debugging output, but it does not affect whether the app’s files are locked during deployment. Either configuration produces deployable binaries, so file lock errors are independent of the chosen configuration.
Visual reference
About these practice questions
Courseiva creates original exam-style practice questions with explanations and wrong-answer analysis. It does not publish real exam questions, exam dumps, or protected exam content. Learn why practice questions differ from exam dumps →
Last reviewed: Jun 11, 2026
This AZ-400 practice question is part of Courseiva's free Microsoft certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the AZ-400 exam.
Question Discussion
Share a tip, memory trick, or ask about the reasoning behind this question. Do not post real exam questions, leaked content, braindumps, or copyrighted exam material. Comments are moderated and may be removed without notice.
Sign in to join the discussion.