# Reflection: You Built a Real Image, Not Just Ran Someone Else's

## Reflection questions

1. Every image you used before this module (nginx, alpine) was built by someone else, from a
   Dockerfile you never saw. Does writing your own change how you think about those images?
2. Which Dockerfile instruction do you expect to use the most in real application work?

## Real Ops takeaway

**A Dockerfile is executable documentation of exactly how an application's environment is
built — the same reproducibility promise ROOT 03's version control made about code, now applied
to environments.** You've closed the loop this course opened with Module 1's "it works on my
machine" problem: a Dockerfile means the environment itself is defined, versioned, and
rebuildable identically anywhere, by anyone, forever.

This module is complete. Continue to the next module.

## Instructor Notes

**Discussion questions for a live classroom:** question 1 is a good moment to reflect on the
"black box → understood mechanism" arc of this entire course.

**Approximate timing:** 5-8 minutes live discussion; 5 minutes self-paced writing.