BuildKit

As explained in Learn Docker in a Month of Lunches, Second Edition

BuildKit is Docker's image-building engine for efficiently constructing container images from build definitions and contexts.

BuildKit optimizes Docker image builds by inspecting the Dockerfile and sending only needed content in the build context. Smaller contexts reduce transfer time, especially when building on a remote engine. section 17.1

Use BuildKit-related context optimizations to:

• Copy only required application folders with precise COPY instructions. section 17.1
• Exclude unnecessary files and folders with .dockerignore instead of adding complex COPY patterns. section 17.1
• Avoid deleting unwanted files in a later layer, because deleted files can remain part of the image layers. section 17.1

Compare build contexts

Build the original image, add .dockerignore, and rebuild without cache: docker image build -t diamol/ch17-build-context:2e-v3 --no-cache .; mv dockerignore.txt .dockerignore; docker image build -t diamol/ch17-build-context:2e-v4 --no-cache .

Figure 17.4 Using a .dockerignore file reduces the size of the build context and the time to send it.

See how .dockerignore reduces the build-context size and the time required to send it. section 17.1

How Learn Docker in a Month of Lunches, Second Edition covers it

How deep it goes

Explains Dockerfile inspection, precise COPY commands, .dockerignore, and image-layer consequences.

Examples

Uses app-folder COPY instructions, a 2 MB image context, .dockerignore, and comparative Docker build commands.

What it assumes

Assumes familiarity with Dockerfiles, COPY instructions, image builds, and build contexts.

What you can do after

Apply it via Docker builds to reduce transferred context and avoid ineffective cleanup layers.

How it connects

Connects BuildKit with Dockerfiles, build contexts, .dockerignore, Docker images, and image layers.

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Related concepts

• Buildxused by · Buildx is a Docker CLI plugin for building container images with advanced capabilities, including multi-platform builds.
• Dockerfileuses · A Dockerfile is a text file containing declarative instructions for building a container image and specifying its contents and runtime metadata.

This explainer was generated by Manning's knowledge graph from the text of Learn Docker in a Month of Lunches, Second Edition. The section links point to the parts of the book it draws on.