What is Docker Buildx and multi-platform builds?

Docker Buildx is Docker's extended build CLI plugin that implements the BuildKit build system with additional capabilities beyond the classic docker build. Key feature: multi-platform builds — building images for multiple CPU architectures (amd64/x86_64, arm64/aarch64, armv7, etc.) from a single build command and publishing a multi-platform image manifest. Why it matters: (1) Apple Silicon Macs (arm64) need arm64 images; (2) Raspberry Pi (arm32/arm64); (3) AWS Graviton (arm64 — cheaper than x86); (4) Shipping one image tag that works everywhere. docker buildx create --name mybuilder --driver docker-container --bootstrap\ndocker buildx use mybuilder\ndocker buildx build --platform linux/amd64,linux/arm64,linux/arm/v7 -t myapp:1.0 --push .. This pushes a manifest list (fat manifest) — myapp:1.0 returns the correct architecture for each puller. Emulation: Buildx uses QEMU emulation to build for foreign architectures on a single host — slower than native. For speed, use --platform linux/amd64 native builders + --platform linux/arm64 on an ARM builder, then docker buildx imagetools create to combine. Builders: Buildx supports multiple drivers — docker (default), docker-container (full BuildKit in a container, supports multi-platform), kubernetes (builds on K8s pods), remote (connect to remote BuildKit).