Understanding Docker Builders and Build Drivers

--- title: Builders weight: 40 keywords: build, buildx, builders, buildkit, drivers, backend description: Learn about builders and how to manage them --- A builder is a BuildKit daemon that you can use to run your builds. BuildKit is the build engine that solves the build steps in a Dockerfile to produce a container image or other artifacts. You can create and manage builders, inspect them, and even connect to builders running remotely. You interact with builders using the Docker CLI. ## Default builder Docker Engine automatically creates a builder that becomes the default backend for your builds. This builder uses the BuildKit library bundled with the daemon. This builder requires no configuration. The default builder is directly bound to the Docker daemon and its [context](/manuals/engine/manage-resources/contexts.md). If you change the Docker context, your `default` builder refers to the new Docker context. ## Build drivers Buildx implements a concept of [build drivers](drivers/_index.md) to refer to different builder configurations. The default builder created by the daemon uses the [`docker` driver](drivers/docker.md). Buildx supports the following build drivers: - `docker`: uses the BuildKit library bundled into the Docker daemon. - `docker-container`: creates a dedicated BuildKit container using Docker. - `kubernetes`: creates BuildKit pods in a Kubernetes cluster. - `remote`: connects directly to a manually managed BuildKit daemon. ## Selected builder Selected builder refers to the builder that's used by default when you run build commands. When you run a build, or interact with builders in some way using the CLI, you can use the optional `--builder` flag, or the `BUILDX_BUILDER` [environment variable](../building/variables.md#buildx_builder), to specify a builder by name. If you don't specify a builder, the selected builder is used. Use the `docker buildx ls` command to see the available builder instances. The asterisk (`*`) next to a builder name indicates the selected builder. ```console $ docker buildx ls NAME/NODE DRIVER/ENDPOINT STATUS BUILDKIT PLATFORMS default * docker default default running v0.11.6 linux/amd64, linux/amd64/v2, linux/amd64/v3, linux/386

This section defines what a builder is in the context of Docker and BuildKit, explaining its role in solving build steps from a Dockerfile. It details the default builder, which is automatically created by Docker Engine, and introduces the concept of build drivers, including 'docker', 'docker-container', 'kubernetes', and 'remote'. It also explains how to select and identify the active builder using the Docker CLI.