AZ-400 Container jobs Practice Question
You are designing a build pipeline that must run on Microsoft-hosted agents. The pipeline has a dependency on a native library that is not pre-installed. You want to minimize pipeline duration. Which approach should you use?
⚠ Common exam trap
Candidates may think self-hosted agents are required for pre-installed dependencies, but container jobs on Microsoft-hosted agents achieve the same benefit with less management overhead and still meet the requirement.
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
✓
Use a container job with a custom Docker image that includes the library
Using a container job with a custom Docker image that includes the native library allows the pipeline to run on Microsoft-hosted agents while eliminating installation overhead, thus minimizing pipeline duration. This approach meets the requirement of using Microsoft-hosted agents and avoids the time cost of installing the library in each run.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Use a container job with a custom Docker image that includes the library
Why this is correct
Using a container job with a custom Docker image that includes the library allows the pipeline to run on Microsoft-hosted agents while avoiding the time needed to install the library in each run. This minimizes pipeline duration and meets the requirement.
- ✗
Use a self-hosted agent with the library pre-installed
Why it's wrong here
Self-hosted agents contradict the stated requirement that the pipeline run on Microsoft-hosted agents, so the dependency cannot be pre-installed there. It tempts because self-hosted agents with baked-in libraries genuinely cut setup time when the constraint is duration alone and hosted agents are not mandated.
- ✗
Add a script step to install the library using a package manager
Why it's wrong here
Installing the library at runtime adds download and installation time to every build, increasing pipeline duration. Baking the dependency into a custom container image or self-hosted agent avoids repeated installation; a package-manager script is the fallback when pre-installation is impossible.
- ✗
Download the library from Azure Blob Storage in each build
Why it's wrong here
Downloading from Blob Storage each run adds network transfer to every build, lengthening duration; caching the library across runs avoids repeated retrieval. Blob download suits one-off artefacts or large files not needed every build, not a recurring native dependency on Microsoft-hosted agents.
Go deeper
Related to this question
Learn chapter
Designing a Build Pipeline
Key term
Library
In Azure DevOps, a Library is a central repository for managing reusable content like variable groups and secure files that can be shared across multiple pipelines.
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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