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`](./solver/pb/ops.proto) for the format definition.
Currently, following high-level languages has been implemented for LLB:
- Dockerfile (See [Exploring Dockerfiles](#exploring-dockerfiles))
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.
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.
`buildctl build` will show interactive progress bar by default while the build job is running. It will also show you the path to the trace file that contains 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`
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.
`--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.
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`.
During development, an external version of the Dockerfile frontend is pushed to https://hub.docker.com/r/tonistiigi/dockerfile that 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](https://github.com/moby/buildkit/issues/163)). For automatic build from master branch of this repository `tonistiigi/dockerfile:master` image can be used.
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.
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.
BuildKit supports opentracing for buildkitd gRPC API and buildctl commands. To capture the trace to [Jaeger](https://github.com/jaegertracing/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/
During development, BuildKit is tested with the version of runc that is being used by the containerd repository. Please refer to [runc.md](https://github.com/containerd/containerd/blob/v1.1.3/RUNC.md) for more information.
This runs all unit and integration tests in a containerized environment. Locally, every package can be tested separately with standard Go tools, but integration tests are skipped if local user doesn't have enough permissions or worker binaries are not installed.
