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moby
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Description

concurrent, cache-efficient, and Dockerfile-agnostic builder toolkit

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BuildKit

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BuildKit is a toolkit for converting source code to build artifacts in an efficient, expressive and repeatable manner.

Key features:

  • Automatic garbage collection
  • Extendable frontend formats
  • Concurrent dependency resolution
  • Efficient instruction caching
  • Build cache import/export
  • Nested build job invocations
  • Distributable workers
  • Multiple output formats
  • Pluggable architecture
  • Execution without root privileges

Read the proposal from https://github.com/moby/moby/issues/32925

Introductory blog post https://blog.mobyproject.org/introducing-buildkit-17e056cc5317

Join

#buildkit
channel on Docker Community Slack

:information_source: If you are visiting this repo for the usage of BuildKit-only Dockerfile features like

RUN --mount=type=(bind|cache|tmpfs|secret|ssh)
, please refer to
frontend/dockerfile/docs/syntax.md
.

:information_source: BuildKit has been integrated to

docker build
since Docker 18.06 . You don't need to read this document unless you want to use the full-featured standalone version of BuildKit.

Used by

BuildKit is used by the following projects:

Quick start

:information_source: For Kubernetes deployments, see

examples/kubernetes
.

BuildKit is composed of the

buildkitd
daemon and the
buildctl
client. While the
buildctl
client is available for Linux, macOS, and Windows, the
buildkitd
daemon is only available for Linux currently.

The

buildkitd
daemon requires the following components to be installed: - runc or crun - containerd (if you want to use containerd worker)

The latest binaries of BuildKit are available here for Linux, macOS, and Windows.

Homebrew package (unofficial) is available for macOS.

console
$ brew install buildkit

To build BuildKit from source, see

.github/CONTRIBUTING.md
.

Starting the
buildkitd
daemon:

You need to run

buildkitd
as the root user on the host.
$ sudo buildkitd

To run

buildkitd
as a non-root user, see
docs/rootless.md
.

The buildkitd daemon supports two worker backends: OCI (runc) and containerd.

By default, the OCI (runc) worker is used. You can set

--oci-worker=false --containerd-worker=true
to use the containerd worker.

We are open to adding more backends.

To start the buildkitd daemon using systemd socket activiation, you can install the buildkit systemd unit files. See Systemd socket activation

The buildkitd daemon listens gRPC API on

/run/buildkit/buildkitd.sock
by default, but you can also use TCP sockets. See Expose BuildKit as a TCP service.

Exploring LLB

BuildKit builds are based on a binary intermediate format called LLB that is used for defining the dependency graph for processes running part of your build. tl;dr: LLB is to Dockerfile what LLVM IR is to C.

  • Marshaled as Protobuf messages
  • Concurrently executable
  • Efficiently cacheable
  • Vendor-neutral (i.e. non-Dockerfile languages can be easily implemented)

See

solver/pb/ops.proto
for the format definition, and see
./examples/README.md
for example LLB applications.

Currently, the following high-level languages has been implemented for LLB:

Exploring Dockerfiles

Frontends are components that run inside BuildKit and convert any build definition to LLB. There is a special frontend called gateway (

gateway.v0
) that allows using any image as a frontend.

During development, Dockerfile frontend (

dockerfile.v0
) is also part of the BuildKit repo. In the future, this will be moved out, and Dockerfiles can be built using an external image.

Building a Dockerfile with
buildctl

buildctl build \
    --frontend=dockerfile.v0 \
    --local context=. \
    --local dockerfile=.
# or
buildctl build \
    --frontend=dockerfile.v0 \
    --local context=. \
    --local dockerfile=. \
    --opt target=foo \
    --opt build-arg:foo=bar

--local
exposes local source files from client to the builder.
context
and
dockerfile
are the names Dockerfile frontend looks for build context and Dockerfile location.

Building a Dockerfile using external frontend:

External versions of the Dockerfile frontend are pushed to https://hub.docker.com/r/docker/dockerfile-upstream and https://hub.docker.com/r/docker/dockerfile and can be used with the gateway frontend. The source for the external frontend is currently located in

./frontend/dockerfile/cmd/dockerfile-frontend
but will move out of this repository in the future (#163). For automatic build from master branch of this repository
docker/dockerfile-upstream:master
or
docker/dockerfile-upstream:master-labs
image can be used.
buildctl build \
    --frontend gateway.v0 \
    --opt source=docker/dockerfile \
    --local context=. \
    --local dockerfile=.
buildctl build \
    --frontend gateway.v0 \
    --opt source=docker/dockerfile \
    --opt context=git://github.com/moby/moby \
    --opt build-arg:APT_MIRROR=cdn-fastly.deb.debian.org

Building a Dockerfile with experimental features like
RUN --mount=type=(bind|cache|tmpfs|secret|ssh)

See

frontend/dockerfile/docs/experimental.md
.

Output

By default, the build result and intermediate cache will only remain internally in BuildKit. An output needs to be specified to retrieve the result.

Image/Registry

buildctl build ... --output type=image,name=docker.io/username/image,push=true

To export the cache embed with the image and pushing them to registry together, type

registry
is required to import the cache, you should specify
--export-cache type=inline
and
--import-cache type=registry,ref=...
. To export the cache to a local directy, you should specify
--export-cache type=local
. Details in Export cache.
buildctl build ...\
  --output type=image,name=docker.io/username/image,push=true \
  --export-cache type=inline \
  --import-cache type=registry,ref=docker.io/username/image

Keys supported by image output: *

name=[value]
: image name *
push=true
: push after creating the image *
push-by-digest=true
: push unnamed image *
registry.insecure=true
: push to insecure HTTP registry *
oci-mediatypes=true
: use OCI mediatypes in configuration JSON instead of Docker's *
unpack=true
: unpack image after creation (for use with containerd) *
dangling-name-prefix=[value]
: name image with
[email protected]
, used for anonymous images *
name-canonical=true
: add additional canonical name
[email protected]
*
compression=[uncompressed,gzip]
: choose compression type for layer, gzip is default value

If credentials are required,

buildctl
will attempt to read Docker configuration file
$DOCKER_CONFIG/config.json
.
$DOCKER_CONFIG
defaults to
~/.docker
.

Local directory

The local client will copy the files directly to the client. This is useful if BuildKit is being used for building something else than container images.

buildctl build ... --output type=local,dest=path/to/output-dir

To export specific files use multi-stage builds with a scratch stage and copy the needed files into that stage with

COPY --from
.
...
FROM scratch as testresult

COPY --from=builder /usr/src/app/testresult.xml . ...

buildctl build ... --opt target=testresult --output type=local,dest=path/to/output-dir

Tar exporter is similar to local exporter but transfers the files through a tarball.

buildctl build ... --output type=tar,dest=out.tar
buildctl build ... --output type=tar > out.tar

Docker tarball

# exported tarball is also compatible with OCI spec
buildctl build ... --output type=docker,name=myimage | docker load

OCI tarball

buildctl build ... --output type=oci,dest=path/to/output.tar
buildctl build ... --output type=oci > output.tar

containerd image store

The containerd worker needs to be used

buildctl build ... --output type=image,name=docker.io/username/image
ctr --namespace=buildkit images ls

To change the containerd namespace, you need to change

worker.containerd.namespace
in
/etc/buildkit/buildkitd.toml
.

Cache

To show local build cache (

/var/lib/buildkit
):
buildctl du -v

To prune local build cache:

bash
buildctl prune

Garbage collection

See

./docs/buildkitd.toml.md
.

Export cache

BuildKit supports the following cache exporters: *

inline
: embed the cache into the image, and push them to the registry together *
registry
: push the image and the cache separately *
local
: export to a local directory

In most case you want to use the

inline
cache exporter. However, note that the
inline
cache exporter only supports
min
cache mode. To enable
max
cache mode, push the image and the cache separately by using
registry
cache exporter.

Inline (push image and cache together)

buildctl build ... \
  --output type=image,name=docker.io/username/image,push=true \
  --export-cache type=inline \
  --import-cache type=registry,ref=docker.io/username/image

Note that the inline cache is not imported unless

--import-cache type=registry,ref=...
is provided.

:informationsource: Docker-integrated BuildKit (`DOCKERBUILDKIT=1 docker build

) and
docker buildx
requires 
--build-arg BUILDKITINLINECACHE=1
to be specified to enable the
inline
cache exporter.
However, the standalone
buildctl
does NOT require
--opt build-arg:BUILDKITINLINECACHE=1` and the build-arg is simply ignored.

Registry (push image and cache separately)

buildctl build ... \
  --output type=image,name=localhost:5000/myrepo:image,push=true \
  --export-cache type=registry,ref=localhost:5000/myrepo:buildcache \
  --import-cache type=registry,ref=localhost:5000/myrepo:buildcache \

Local directory

buildctl build ... --export-cache type=local,dest=path/to/output-dir
buildctl build ... --import-cache type=local,src=path/to/input-dir

The directory layout conforms to OCI Image Spec v1.0.

--export-cache
options

  • type
    :
    inline
    ,
    registry
    , or
    local
  • mode=min
    (default): only export layers for the resulting image
  • mode=max
    : export all the layers of all intermediate steps. Not supported for
    inline
    cache exporter.
  • ref=docker.io/user/image:tag
    : reference for
    registry
    cache exporter
  • dest=path/to/output-dir
    : directory for
    local
    cache exporter
  • oci-mediatypes=true|false
    : whether to use OCI mediatypes in exported manifests for
    local
    and
    registry
    exporter. Since BuildKit
    v0.8
    defaults to true.

--import-cache
options

  • type
    :
    registry
    or
    local
    . Use
    registry
    to import
    inline
    cache.
  • ref=docker.io/user/image:tag
    : reference for
    registry
    cache importer
  • src=path/to/input-dir
    : directory for
    local
    cache importer
  • digest=sha256:deadbeef
    : digest of the manifest list to import for
    local
    cache importer.
  • tag=customtag
    : custom tag of image for
    local
    cache importer. Defaults to the digest of "latest" tag in
    index.json
    is for digest, not for tag

Consistent hashing

If you have multiple BuildKit daemon instances but you don't want to use registry for sharing cache across the cluster, consider client-side load balancing using consistent hashing.

See

./examples/kubernetes/consistenthash
.

Systemd socket activation

On Systemd based systems, you can communicate with the daemon via Systemd socket activation, use

buildkitd --addr fd://
. You can find examples of using Systemd socket activation with BuildKit and Systemd in
./examples/systemd
.

Expose BuildKit as a TCP service

The

buildkitd
daemon can listen the gRPC API on a TCP socket.

It is highly recommended to create TLS certificates for both the daemon and the client (mTLS). Enabling TCP without mTLS is dangerous because the executor containers (aka Dockerfile

RUN
containers) can call BuildKit API as well.
buildkitd \
  --addr tcp://0.0.0.0:1234 \
  --tlscacert /path/to/ca.pem \
  --tlscert /path/to/cert.pem \
  --tlskey /path/to/key.pem
buildctl \
  --addr tcp://example.com:1234 \
  --tlscacert /path/to/ca.pem \
  --tlscert /path/to/clientcert.pem \
  --tlskey /path/to/clientkey.pem \
  build ...

Load balancing

buildctl build
can be called against randomly load balanced the
buildkitd
daemon.

See also Consistent hashing for client-side load balancing.

Containerizing BuildKit

BuildKit can also be used by running the

buildkitd
daemon inside a Docker container and accessing it remotely.

We provide the container images as

moby/buildkit
:

  • moby/buildkit:latest
    : built from the latest regular release
  • moby/buildkit:rootless
    : same as
    latest
    but runs as an unprivileged user, see
    docs/rootless.md
  • moby/buildkit:master
    : built from the master branch
  • moby/buildkit:master-rootless
    : same as master but runs as an unprivileged user, see
    docs/rootless.md

To run daemon in a container:

docker run -d --name buildkitd --privileged moby/buildkit:latest
export BUILDKIT_HOST=docker-container://buildkitd
buildctl build --help

Podman

To connect to a BuildKit daemon running in a Podman container, use

podman-container://
instead of
docker-container://
.
podman run -d --name buildkitd --privileged moby/buildkit:latest
buildctl --addr=podman-container://buildkitd build --frontend dockerfile.v0 --local context=. --local dockerfile=. --output type=oci | podman load foo

sudo
is not required.

Kubernetes

For Kubernetes deployments, see

examples/kubernetes
.

Daemonless

To run the client and an ephemeral daemon in a single container ("daemonless mode"):

docker run \
    -it \
    --rm \
    --privileged \
    -v /path/to/dir:/tmp/work \
    --entrypoint buildctl-daemonless.sh \
    moby/buildkit:master \
        build \
        --frontend dockerfile.v0 \
        --local context=/tmp/work \
        --local dockerfile=/tmp/work

or

docker run \
    -it \
    --rm \
    --security-opt seccomp=unconfined \
    --security-opt apparmor=unconfined \
    -e BUILDKITD_FLAGS=--oci-worker-no-process-sandbox \
    -v /path/to/dir:/tmp/work \
    --entrypoint buildctl-daemonless.sh \
    moby/buildkit:master-rootless \
        build \
        --frontend \
        dockerfile.v0 \
        --local context=/tmp/work \
        --local dockerfile=/tmp/work

Opentracing support

BuildKit supports opentracing for buildkitd gRPC API and buildctl commands. To capture the trace to Jaeger, set

JAEGER_TRACE
environment variable to the collection address.
docker run -d -p6831:6831/udp -p16686:16686 jaegertracing/all-in-one:latest
export JAEGER_TRACE=0.0.0.0:6831
# restart buildkitd and buildctl so they know JAEGER_TRACE
# any buildctl command should be traced to http://127.0.0.1:16686/

Running BuildKit without root privileges

Please refer to

docs/rootless.md
.

Building multi-platform images

See

docker buildx
documentation

Contributing

Want to contribute to BuildKit? Awesome! You can find information about contributing to this project in the CONTRIBUTING.md

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