AZ-400 Practice Question: Design and implement build and release pipelines
Network Topology
Refer to the exhibit. A developer queues a build manually but notices the build status remains 'notStarted' for an extended period. The pipeline has no demands and priority is normal. Which is the most likely cause?
⚠ Common exam trap
It's easy for candidates to assume a 'notStarted' status is caused by a configuration error (like a missing branch or misspelled variable) rather than recognizing it as a classic symptom of agent pool exhaustion or queue saturation.
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
✓
All agents in the pool are currently busy.
When a build remains in 'notStarted' status for an extended period, it typically means the pipeline is waiting for an available agent. Since the pipeline has no demands and priority is normal, the most likely cause is that all agents in the specified agent pool are currently busy executing other jobs, so the build is queued until an agent becomes free.
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 variable 'BuildConfiguration' is misspelled.
Why it's wrong here
Azure Pipelines variable names are case-insensitive, meaning 'BuildConfiguration' and 'buildconfiguration' are treated as the same variable. A misspelling would not prevent the build from being queued; at most, it would cause the variable to expand to an empty string or trigger a pipeline error during execution when referenced. Therefore, a misspelled variable cannot explain a build that is stuck in the queue.
- ✗
The branch 'main' does not exist.
Why it's wrong here
Azure DevOps validates the branch name against the repository during the queue operation; if the branch 'main' did not exist, the service would fail the queue request immediately with a 'Branch not found' error, and no build would be created. A build that appears in the queue waiting for an agent means the branch reference was accepted at queue time. Therefore, a non-existent branch would have prevented the build from ever being queued, making it an invalid explanation.
- ✓
All agents in the pool are currently busy.
Why this is correct
When a build is queued without explicit agent demands, Azure Pipelines can run it on any agent in the specified pool. If all agents in that pool are currently executing other jobs, the build will remain in a queued state until an agent becomes available—this is a common cause of a build appearing stuck. The queue shows the build as 'Queued' or 'Waiting for agent' without raising an immediate error, which matches the exhibit behavior.
- ✗
The pipeline definition ID is incorrect.
Why it's wrong here
An invalid pipeline definition ID would be rejected by the Azure DevOps REST API at the moment the build is queued, returning an error such as 404 and creating no build record. Since the exhibit shows a build that was successfully queued and is still waiting, the definition ID must have been valid; otherwise, the queue request would have failed immediately. Thus, an incorrect definition ID cannot be the reason the build is not progressing.
Go deeper
Related to this question
Learn chapter
Designing a Build Pipeline
Key term
Agent
An agent is a software component that runs on a local machine to perform automated tasks, collect data, or execute commands as part of a larger system like CI/CD or monitoring.
Key term
Pipeline
A pipeline is an automated series of steps that takes code from development to production, ensuring quality and speed.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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