BuildKit for improved builds in Docker - Commands & Configuration

Introduction

Building Docker images can be slow and inefficient. BuildKit is a modern builder that speeds up builds, reduces image size, and improves caching to save time and resources.

When you want faster Docker image builds for your application.

When you need to use advanced caching to avoid rebuilding unchanged parts.

When you want to build multi-stage Dockerfiles more efficiently.

When you want better output logs that are easier to read.

When you want to build images with secrets or SSH keys safely.

Commands

This command enables BuildKit for your Docker client session to improve build performance and features.

Terminal

export DOCKER_BUILDKIT=1

Expected Output

No output (command runs silently)

Builds the Docker image named 'my-app' using BuildKit, which is enabled by the environment variable set earlier.

Terminal

docker build -t my-app:latest .

Expected Output

#1 [internal] load build definition from Dockerfile

#1 sha256:abcdef1234567890abcdef1234567890abcdef1234567890abcdef1234567890

#1 transferring dockerfile: 123B done

#1 DONE 0.1s



#2 [internal] load .dockerignore

#2 sha256:123456abcdef123456abcdef123456abcdef123456abcdef123456abcdef123456

#2 transferring context: 2B done

#2 DONE 0.1s



#3 [internal] load metadata for docker.io/library/python:3.10-slim

#3 sha256:abcdefabcdefabcdefabcdefabcdefabcdefabcdefabcdefabcdefabcdefabcdef

#3 DONE 1.2s



#4 [1/5] FROM docker.io/library/python:3.10-slim@sha256:abcdefabcdefabcdefabcdefabcdefabcdefabcdefabcdefabcdefabcdefabcdef

#4 DONE 0.0s



#5 [2/5] WORKDIR /app

#5 DONE 0.0s



#6 [3/5] COPY requirements.txt ./

#6 DONE 0.0s



#7 [4/5] RUN pip install -r requirements.txt

#7 DONE 3.5s



#8 [5/5] COPY . .

#8 DONE 0.1s



#9 exporting to image

#9 sha256:abcdefabcdefabcdefabcdefabcdefabcdefabcdefabcdefabcdefabcdefabcdef

#9 exporting layers

#9 writing image sha256:abcdefabcdefabcdefabcdefabcdefabcdefabcdefabcdefabcdefabcdefabcdef done

#9 naming to docker.io/library/my-app:latest done



Use 'docker scan' to run Snyk tests against images to find vulnerabilities and learn how to fix them

→

-t - Assigns a name and optionally a tag to the image

Lists the available BuildKit builder instances to verify BuildKit is active and see builder details.

Terminal

docker buildx ls

Expected Output

NAME/NODE       DRIVER/ENDPOINT             STATUS  PLATFORMS

default *       docker-container           running linux/amd64, linux/arm64, linux/arm/v7

Key Concept

If you remember nothing else from this pattern, remember: enabling BuildKit speeds up Docker builds and improves caching automatically.

Common Mistakes

Not enabling BuildKit before running docker build.

Docker uses the older builder by default, missing out on speed and caching improvements.

Run 'export DOCKER_BUILDKIT=1' in your terminal before building images.

Using outdated Docker versions that do not support BuildKit.

BuildKit requires Docker 18.09 or newer to work properly.

Update Docker to the latest stable version to use BuildKit features.

Summary

Enable BuildKit by setting the environment variable DOCKER_BUILDKIT=1.

Build images with 'docker build' to get faster builds and better caching.

Use 'docker buildx ls' to check active BuildKit builders and platforms.

Practice

1. What is the main purpose of enabling BuildKit in Docker builds?

easy

A. To speed up builds and provide smarter build features

B. To disable caching during Docker builds

C. To automatically push images to Docker Hub

D. To run containers in debug mode

Solution

1. Step 1: Understand BuildKit's role

   BuildKit is designed to improve Docker build speed and add smarter features like better caching and parallel steps.

2. Step 2: Compare options

   Options A, C, and D describe unrelated Docker features. Only To speed up builds and provide smarter build features correctly describes BuildKit's purpose.

3. Final Answer:

   To speed up builds and provide smarter build features -> Option A

4. Quick Check:

   BuildKit purpose = speed and smart builds [OK]

Hint: BuildKit improves build speed and features, not disables or pushes [OK]

Common Mistakes:

• Thinking BuildKit disables cache
• Confusing BuildKit with image pushing
• Assuming BuildKit runs containers

2. Which command correctly enables BuildKit for a Docker build?

easy

A. docker build --enable-buildkit .

B. docker build --buildkit=enable .

C. docker build -buildkit 1 .

D. DOCKER_BUILDKIT=1 docker build .

Solution

1. Step 1: Recall how to enable BuildKit

   BuildKit is enabled by setting the environment variable DOCKER_BUILDKIT=1 before running the docker build command.

2. Step 2: Analyze options

   Only DOCKER_BUILDKIT=1 docker build . uses the correct environment variable syntax. Options B, C, and D use invalid flags or syntax.

3. Final Answer:

   DOCKER_BUILDKIT=1 docker build . -> Option D

4. Quick Check:

   Enable BuildKit with env var DOCKER_BUILDKIT=1 [OK]

Hint: Set DOCKER_BUILDKIT=1 before docker build command [OK]

Common Mistakes:

• Using invalid flags like --buildkit=enable
• Trying to pass BuildKit as a docker build option
• Forgetting to set environment variable

3. What output difference will you see when running DOCKER_BUILDKIT=1 docker build . compared to a normal build?

medium

A. More detailed and clearer build step output

B. No output is shown during the build

C. Build output is shown in JSON format only

D. Build output is slower and less informative

Solution

1. Step 1: Understand BuildKit output changes

   BuildKit provides clearer, more detailed output with progress bars and parallel step info.

2. Step 2: Compare output options

   More detailed and clearer build step output matches this behavior. Options B and D are incorrect because output is shown and faster. Build output is shown in JSON format only is wrong because JSON output is not default.

3. Final Answer:

   More detailed and clearer build step output -> Option A

4. Quick Check:

   BuildKit output = clearer and detailed [OK]

Hint: BuildKit shows clearer, detailed build progress output [OK]

Common Mistakes:

• Expecting no output during build
• Thinking output is JSON by default
• Assuming BuildKit slows down output

4. You tried to enable BuildKit with docker build --buildkit=1 . but it failed. What is the likely cause?

medium

A. BuildKit is not supported on your Docker version

B. The flag --buildkit=1 is invalid; BuildKit must be enabled via environment variable

C. You need to add --enable-buildkit flag instead

D. You must run docker build as root to enable BuildKit

Solution

1. Step 1: Check how BuildKit is enabled

   BuildKit is enabled by setting the environment variable DOCKER_BUILDKIT=1, not by a docker build flag.

2. Step 2: Analyze the error cause

   Using --buildkit=1 is invalid syntax, causing the failure. Options B, C, and D are incorrect because BuildKit is supported in recent Docker versions, no such flag exists, and root is not required.

3. Final Answer:

   The flag --buildkit=1 is invalid; BuildKit must be enabled via environment variable -> Option B

4. Quick Check:

   BuildKit enabled only by env var, not flags [OK]

Hint: BuildKit enabled only by DOCKER_BUILDKIT=1 env var [OK]

Common Mistakes:

• Trying to enable BuildKit with invalid flags
• Assuming root permission is needed
• Believing BuildKit is disabled on all Docker versions

5. You want to speed up your Docker build by using BuildKit and also use a cache from a previous build stored locally. Which command correctly achieves this?

hard

A. docker build --cache-from=type=local,src=/path/to/cache .

B. docker build --buildkit=1 --cache-from=local:/path/to/cache .

C. DOCKER_BUILDKIT=1 docker build --cache-from=type=local,src=/path/to/cache .

D. DOCKER_BUILDKIT=1 docker build --cache-from=local:/path/to/cache .

Solution

1. Step 1: Enable BuildKit correctly

   BuildKit must be enabled by setting DOCKER_BUILDKIT=1 environment variable before the docker build command.

2. Step 2: Use correct cache-from syntax

   BuildKit supports advanced cache-from syntax like --cache-from=type=local,src=path. DOCKER_BUILDKIT=1 docker build --cache-from=type=local,src=/path/to/cache . uses this correctly. Options B and C use invalid flags or syntax. docker build --cache-from=type=local,src=/path/to/cache . misses enabling BuildKit.

3. Final Answer:

   DOCKER_BUILDKIT=1 docker build --cache-from=type=local,src=/path/to/cache . -> Option C

4. Quick Check:

   Enable BuildKit + correct cache-from syntax = DOCKER_BUILDKIT=1 docker build --cache-from=type=local,src=/path/to/cache . [OK]

Hint: Set DOCKER_BUILDKIT=1 and use --cache-from=type=local,src=path [OK]

Common Mistakes:

• Using --buildkit=1 flag instead of env var
• Incorrect cache-from syntax
• Forgetting to enable BuildKit