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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
ℹ If you are visiting this repo for the usage of experimental Dockerfile features like RUN --mount=type=(bind|cache|tmpfs|secret|ssh)
, please refer to frontend/dockerfile/docs/experimental.md
.
Used by
BuildKit is used by the following projects:
Quick start
Dependencies:
The following command installs buildkitd
and buildctl
to /usr/local/bin
:
$ make && sudo make install
You can also use make binaries-all
to prepare buildkitd.containerd_only
and buildkitd.oci_only
.
Starting the buildkitd daemon:
buildkitd --debug --root /var/lib/buildkit
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.
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.
Currently, following high-level languages has been implemented for LLB:
For understanding the basics of LLB, examples/buildkit*
directory contains scripts that define how to build different configurations of BuildKit itself and its dependencies using the client
package. Running one of these scripts generates a protobuf definition of a build graph. Note that the script itself does not execute any steps of the build.
You can use buildctl debug dump-llb
to see what data is in this definition. Add --dot
to generate dot layout.
go run examples/buildkit0/buildkit.go \
| buildctl debug dump-llb \
| jq .
To start building use buildctl build
command. The example script accepts --with-containerd
flag to choose if containerd binaries and support should be included in the end result as well.
go run examples/buildkit0/buildkit.go \
| buildctl build
buildctl build
will show interactive progress bar by default while the build job is running. If the path to the trace file is specified, the trace file generated will contain all information about the timing of the individual steps and logs.
Different versions of the example scripts show different ways of describing the build definition for this project to show the capabilities of the library. New versions have been added when new features have become available.
./examples/buildkit0
- uses only exec operations, defines a full stage per component.
./examples/buildkit1
- cloning git repositories has been separated for extra concurrency.
./examples/buildkit2
- uses git sources directly instead of running git clone
, allowing better performance and much safer caching.
./examples/buildkit3
- allows using local source files for separate components eg. ./buildkit3 --runc=local | buildctl build --local runc-src=some/local/path
./examples/dockerfile2llb
- can be used to convert a Dockerfile to LLB for debugging purposes
./examples/gobuild
- shows how to use nested invocation to generate LLB for Go package internal dependencies
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.
build-using-dockerfile utility
For people familiar with docker build
command, there is an example wrapper utility in ./examples/build-using-dockerfile
that allows building Dockerfiles with BuildKit using a syntax similar to docker build
.
go build ./examples/build-using-dockerfile \
&& sudo install build-using-dockerfile /usr/local/bin
build-using-dockerfile -t myimage .
build-using-dockerfile -t mybuildkit -f ./hack/dockerfiles/test.Dockerfile .
# build-using-dockerfile will automatically load the resulting image to Docker
docker inspect myimage
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-upsteam:master
or docker/dockerfile-upstream:master-experimental
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.
Exporting resulting image to containerd
The containerd worker needs to be used
buildctl build ... --output type=image,name=docker.io/username/image
ctr --namespace=buildkit images ls
Push resulting image to registry
buildctl build ... --output type=image,name=docker.io/username/image,push=true
If credentials are required, buildctl
will attempt to read Docker configuration file.
Exporting build result back to client
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
Exporting built image to Docker
# exported tarball is also compatible with OCI spec
buildctl build ... --output type=docker,name=myimage | docker load
buildctl build ... --output type=oci,dest=path/to/output.tar
buildctl build ... --output type=oci > output.tar
Exporting/Importing build cache (not image itself)
To/From registry
buildctl build ... --export-cache type=registry,ref=localhost:5000/myrepo:buildcache
buildctl build ... --import-cache type=registry,ref=localhost:5000/myrepo:buildcache
To/From local filesystem
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
mode=min
(default): only export layers for the resulting image
mode=max
: export all the layers of all intermediate steps
ref=docker.io/user/image:tag
: reference for registry
cache exporter
dest=path/to/output-dir
: directory for local
cache exporter
--import-cache
options
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. Defaults to the digest of "latest" tag in index.json
Other
View build cache
buildctl du -v
Show enabled workers
buildctl debug workers -v
Running containerized buildkit
BuildKit can also be used by running the buildkitd
daemon inside a Docker container and accessing it remotely. The client tool buildctl
is also available for Mac and Windows.
We provide buildkitd
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 --privileged -p 1234:1234 moby/buildkit:latest --addr tcp://0.0.0.0:1234
export BUILDKIT_HOST=tcp://0.0.0.0:1234
buildctl build --help
To run 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
The images can be also built locally using ./hack/dockerfiles/test.Dockerfile
(or ./hack/dockerfiles/test.buildkit.Dockerfile
if you already have BuildKit). Run make images
to build the images as moby/buildkit:local
and moby/buildkit:local-rootless
.
Connection helpers
If you are running moby/buildkit:master
or moby/buildkit:master-rootless
as a Docker/Kubernetes container, you can use special BUILDKIT_HOST
URL for connecting to the BuildKit daemon in the container:
export BUILDKIT_HOST=docker-container://<container>
export BUILDKIT_HOST=kube-pod://<pod>
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/
Supported runc version
During development, BuildKit is tested with the version of runc that is being used by the containerd repository. Please refer to runc.md for more information.
Running BuildKit without root privileges
Please refer to docs/rootless.md
.
Contributing
Want to contribute to BuildKit? Awesome! You can find information about contributing to this project in the CONTRIBUTING.md