https://github.com/IITC-College/express-js-app

Learning Goals

• Understand how Dockerfile instruction order affects build time
• See how small code changes can invalidate Docker cache
• Understand why image size stays the same while build performance changes
• Learn Dockerfile ordering best practices used in production environments

Part 1 — Understand Docker Cache Behavior

Tasks

1. Inspect a previously built image using:

docker history <image-name>

1. Review the layer order.
2. Think about the following question:

• What happens to all layers after a changed layer?

Important Concepts

Docker cache is based on layer hashing.

If one layer changes:

• that layer is rebuilt
• every layer after it is rebuilt as well