# Docker Buildx — Extended Build Capabilities with BuildKit

> A Docker CLI plugin that extends docker build with multi-platform builds, distributed caching, and advanced BuildKit features.

## Install

Save in your project root:

# Docker Buildx — Extended Build Capabilities with BuildKit

## Quick Use
```bash
# Create a new builder instance
docker buildx create --name mybuilder --use
# Build for multiple platforms and push
docker buildx build --platform linux/amd64,linux/arm64 
  -t myrepo/myimage:latest --push .
# Inspect available builders
docker buildx ls
```

## Introduction
Docker Buildx is a CLI plugin that extends the standard `docker build` command with full access to BuildKit features. It enables multi-platform image builds, distributed build caching, multiple builder instances, and advanced Dockerfile capabilities that go beyond what the legacy Docker build engine supports.

## What Docker Buildx Does
- Builds multi-platform container images (amd64, arm64, armv7, s390x, etc.) in a single command
- Manages multiple builder instances with different configurations and drivers
- Supports remote cache backends (registry, S3, GitHub Actions cache, Azure Blob)
- Enables concurrent multi-stage builds with BuildKit's dependency-aware parallelism
- Outputs images to registries, local tarballs, or OCI image layouts

## Architecture Overview
Buildx acts as a frontend to BuildKit, the next-generation build engine. When you run `docker buildx build`, the CLI sends the build context and Dockerfile to a BuildKit daemon. BuildKit parses the Dockerfile into an LLB (low-level build) graph, executes build steps in parallel where possible, and manages layer caching. For multi-platform builds, Buildx uses QEMU emulation or native builder nodes to produce images for each target architecture, then assembles a manifest list.

## Self-Hosting & Configuration
- Included by default in Docker Desktop; on Linux, install as a CLI plugin in ~/.docker/cli-plugins/
- Create builder instances with `docker buildx create` using the docker, docker-container, or kubernetes driver
- Configure remote cache with `--cache-to` and `--cache-from` flags (registry, local, S3, GHA)
- Set default builder with `docker buildx use <name>` or the BUILDX_BUILDER env var
- Use `docker buildx bake` with HCL/JSON files for complex multi-target build definitions

## Key Features
- Multi-platform builds: produce images for multiple CPU architectures from a single machine
- Build drivers: docker (default), docker-container (isolated BuildKit), kubernetes (build pods), or remote
- Bake: declarative build definitions in HCL or JSON for monorepo and multi-image projects
- Distributed caching: share layer caches across CI runners via registry or object storage
- Attestations: generate SBOM and SLSA provenance metadata attached to built images

## Comparison with Similar Tools
- **docker build (legacy)** — single-platform builds with limited caching; Buildx adds multi-platform and advanced cache
- **BuildKit (standalone)** — the underlying engine; Buildx provides a user-friendly Docker CLI integration
- **Kaniko** — builds images in Kubernetes without Docker daemon; Buildx requires a Docker or BuildKit daemon
- **Podman build** — daemonless builds; Buildx offers more advanced caching and multi-platform support via BuildKit

## FAQ
**Q: How do multi-platform builds work without target hardware?**
A: Buildx uses QEMU user-mode emulation registered via binfmt_misc. For faster builds, you can connect native builder nodes for each architecture.

**Q: Can I use Buildx in CI/CD?**
A: Yes. Buildx is widely used in GitHub Actions, GitLab CI, and other CI systems. The `docker/build-push-action` GitHub Action uses Buildx internally.

**Q: What is the difference between Buildx and BuildKit?**
A: BuildKit is the build engine. Buildx is the Docker CLI plugin that makes BuildKit features accessible through familiar `docker build` commands.

**Q: Does Buildx replace docker build?**
A: On modern Docker versions, `docker build` already uses Buildx as the default builder. The `docker buildx` subcommand exposes additional features like builder management and bake.

## Sources
- https://github.com/docker/buildx
- https://docs.docker.com/build/

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Source: https://tokrepo.com/en/workflows/asset-a3c168d1
Author: AI Open Source