What is buildx?

Buildx is an extension of Docker’s command-line tool that lets you build container images with extra features, like building for multiple CPU architectures at once or using advanced caching. It works as a plug-in, so you can keep using the familiar “docker build” syntax while getting more power.

Let's break it down

  • Docker: a platform that packages software into lightweight containers.
  • Extension / plug-in: an add-on that adds new capabilities to an existing program.
  • Build: the process of turning source code and files into a container image.
  • Multiple CPU architectures: different types of processors (e.g., x86, ARM) that need different versions of the same image.
  • Advanced caching: storing intermediate steps so future builds are faster.

Why does it matter?

Buildx lets developers create images that run everywhere-on laptops, servers, or tiny IoT devices-without writing separate Dockerfiles for each platform. It also speeds up CI/CD pipelines, saving time and computing resources.

Where is it used?

  • A CI system (like GitHub Actions) that builds a single image for both Linux-x86_64 and Linux-ARM64 so the same release works on cloud VMs and Raspberry Pi devices.
  • A company that needs to ship a microservice to multiple cloud providers, each with different underlying hardware.
  • Open-source projects that publish multi-arch images on Docker Hub so users can pull the right version automatically.
  • Local development environments where developers test their code on both AMD and Apple Silicon Macs without extra setup.

Good things about it

  • Supports multi-architecture builds in one command.
  • Uses BuildKit under the hood, giving faster and more efficient builds.
  • Works with existing Docker commands, so the learning curve is low.
  • Allows custom build contexts and front-ends (e.g., Dockerfile, Buildpacks).
  • Can push images to multiple registries simultaneously.

Not-so-good things

  • Requires Docker Engine 19.03+ and BuildKit enabled, which may need extra configuration on older setups.
  • Some advanced features (like cache import/export) are still experimental and can be unstable.
  • Debugging multi-arch builds can be harder because errors may appear only on specific architectures.
  • Not all third-party Docker tools have full support for the buildx syntax yet.