Docker BuildKit

The modern Docker build engine providing concurrent builds and advanced features.

Edit Concept ✏️

Docker BuildKit

BuildKit is the next-generation build engine for Docker. It was introduced in Docker 18.09 and is now the default engine.

Key Advantages over the Legacy Builder

  • Concurrent Execution: BuildKit can analyze the dependency graph of your Dockerfile and run independent stages in parallel.
  • Improved Caching: Supports more efficient caching, including remote cache backends.
  • Secret Mounting: Allows you to pass secrets (like API keys or SSH keys) to the build process without them ever being stored in the final image or build metadata.
  • SSH Forwarding: Can forward your host’s SSH agent to the container during build time to access private repositories.
  • Better Output: Provides a much more readable, interactive progress display.

New Dockerfile Instructions (--mount)

BuildKit introduces the --mount flag for RUN instructions:

  • RUN --mount=type=cache: Persistent cache for package managers (e.g., npm or apt cache).
  • RUN --mount=type=secret: Access a secret file during the build.
  • RUN --mount=type=ssh: Use SSH keys from the host.

Enabling BuildKit

If not already the default, it can be enabled via the environment variable: export DOCKER_BUILDKIT=1