BuildKit Container Build Engine

BuildKit is a free and open-source concurrent, cache-efficient, and Dockerfile-agnostic container image builder that serves as the next-generation build backend for Docker and other container build tools. Developed by Docker Inc. (originally by Tonis Tiigi, headquartered in San Francisco) and first released in 2017, BuildKit became the default build engine for Docker Engine starting with Docker 23.0 (2023). Key features: concurrent build execution: BuildKit resolves and executes independent build steps in parallel, dramatically reducing build times compared to the legacy Docker builder which executed steps sequentially. Multiple stages of a multi-stage Dockerfile can be built concurrently when they don't depend on each other. Smart layer caching: BuildKit tracks the exact build graph and caches layers at the instruction level. Cache can be stored locally or exported to remote registries (via --cache-from and --cache-to) for sharing across machines and CI pipelines. Lazy evaluation: BuildKit only builds the parts of the graph that are actually needed for the final output, skipping intermediate stages that don't contribute to the result. Build secrets: securely pass secrets (SSH keys, API tokens, passwords) into build contexts using --secret and RUN --mount=type=secret, ensuring secrets are not stored in the image layers. SSH agent forwarding: forward SSH agent socket into builds (RUN --mount=type=ssh) for cloning private repositories without exposing SSH keys. Multi-platform builds: build images for multiple architectures (amd64, arm64, arm/v7, s390x, ppc64le) from a single build invocation using QEMU emulation or cross-compilation. Output formats: output to Docker daemon, OCI image tarballs, local directories, or push directly to registries. Frontend support: supports Dockerfiles and BuildKit frontend containers for alternative build formats (Buildpacks, Earthly, Bazel). gRPC API for programmatic use. Apache-2.0.