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Containerization · easy

3. Images, Layers, and Build Cache

How Docker builds reusable filesystem layers efficiently.

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A Docker image is composed of read-only layers. Each Dockerfile instruction can create a layer, and the build cache reuses unchanged layers. Put stable dependency installation before frequently changing application source so edits do not invalidate expensive steps.

Use a precise .dockerignore file to keep secrets, build output, and large local directories out of the build context. Pin base image versions or digests when reproducibility matters.

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Check your understanding

  1. 1. Why should dependency installation usually appear before copying frequently changing source code?

  2. 2. What does .dockerignore control?

  3. 3. Why pin a base image digest in a production build?

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