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Debugging a Packer Build

Packer lets us quickly and easily build machine images — at least, it does when everything works. Luckily, Packer provides us with two methods of debugging and testing our builds: the `-debug` flag and the breakpoint provisioner. In this lab, we'll use both of these tools to troubleshoot a troublesome build.

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Level
Clock icon Intermediate
Duration
Clock icon 30m
Last updated
Clock icon Aug 31, 2025

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Table of Contents

  1. Challenge

    Test Build and Troubleshoot

    1. Test the build.
    2. Proceed until the build fails.
    3. In another terminal session, log in to the server a second time. Look for the LXD container from this build and access it via SSH.
    4. Troubleshoot.
    5. For some reason, our file downloaded as an HTML file, not a proper gzip archive! Should we look at the file itself, we can see we're being redirected. We can now close this window, finish our -debug Packer build, and take a look at our script where we download the Prometheus file.
    6. We pull down our gzip file on line 12. The curl command is properly structured, and it does pull down a file, but we'll need to add the -L flag, which will follow any redirects.
    7. Save and exit the file.

  2. Challenge

    Add the Breakpoint Provisioner

    Before we proceed with testing our fix, we want to add one more provisioner to our packer.json file to test our work and ensure Prometheus is running after our provisioning step runs successfully.

  3. Challenge

    Test the Build

    1. Run the build.
    2. When you hit the first breakpoint provisioner, access the Packer container and check the file type of the download.
    3. Stay logged in to the container as you progress to the next breakpoint, and then confirm Prometheus is working.
    4. Allow the build to finish.
Pluralsight Skills - Labs - Pluralsight
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Pluralsight Skills

Pluralsight Skills gives leaders confidence they have the skills needed to execute technology strategy. Technology teams can benchmark expertise across roles, speed up release cycles and build reliable, secure products. By leveraging our expert content, skill assessments and one-of-a-kind analytics, keep up with the pace of change, put the right people on the right projects and boost productivity. It's the most effective path to developing tech skills at scale.

What's a lab?

Hands-on Labs are real environments created by industry experts to help you learn. These environments help you gain knowledge and experience, practice without compromising your system, test without risk, destroy without fear, and let you learn from your mistakes. Hands-on Labs: practice your skills before delivering in the real world.

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We will provide the credentials and environment necessary for you to practice right within your browser.

Guided walkthrough

Follow along with the author’s guided walkthrough and build something new in your provided environment!

Did you know?

On average, you retain 75% more of your learning if you get time for practice.
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