Calico go-build

Base image for doing golang builds for the various project calico builds.

Building the image

To build the image:

make image

The above will build for whatever architecture you are running on. To force a different architecture:

ARCH=<somearch> make image

Tagging

The image is tagged the version, e.g. v0.9 or latest. In addition, the given architecture is appended to the end. Thus, for example, the latest version on amd64 will be calico/go-build:latest-amd64.

The above tagging scheme keeps everything in a single image repository calico/go-build and prepares for using milti-architecture image manifests.

As of this writing, the only way to create such manifests is using the manifest-tool, which involves multiple steps. This can be incorporated into the build process, or we can wait until docker manifest is rolled into the docker CLI, see this PR.

Until such time as the docker manifest is ready, or we decide to use manifest-tool, the default image name will point to amd64. Thus, calico/go-build:latest refers to calico/go-build:latest-amd64.

Cross building using go-build:

Any supported platform can be built natively from its own platform, i.e.g amd64 from amd64, arm64 from arm64 and ppc64le from ppc64le. In addition, ppc64le and arm64 are supported for cross-building from amd64 only. We do not (yet) support cross-building from arm64 and ppc64le.

The cross-build itself will function normally on any platform, since golang supports cross-compiling using GOARCH=<target> go build .

docker run -e GOARCH=<somearch> calico/go-build:latest-amd64 sh -c 'go build hello.go || ./hello'

The above will output a binary hello built for the architecture <somearch>.

Cross-runnning Binaries binfmt

The Linux kernel has the ability to run binaries built for one arch on another, e.g. arm64 binaries on an amd64 architecture. Support requires two things:

Registering an interpeter that can run the binary for the other architecture along with configuration information on how to identify which binaries are for which platform and which emulator will handle them.
Making the interpreter binary available.

The interpreter must exist in one of two places:

The container where you are running the other-architecture binary.
The container where you run registration, if you pass the correct flag during registration. This is supported only from Linux kernel version 4.8+.

For example, if you registered the s390x emulator at /usr/bin/qemu-s390x-static, and then wanted to run docker run -it --rm s390x/alpine:3.10 sh on an amd64, it wouldn't work in the first method, because the new container doesn't have an emulator in it. However, if you followed the second method, it would work, since the kernel already found and loaded the emulator. This works even if you delete the registration container.

To register emulators, we run:

docker run -it --rm --privileged multiarch/qemu-user-static:register

or simply

make register

After the above registration, your system can handle other-architecture binaries. The above registration uses the first method, since all kernels that support binfmt support this method, while only kernels from version 4.8+ support the latter. While docker-for-mac and docker-for-windows both use supporting kernels, almost every CI-as-a-service does not.

Using binfmt in other Calico projects

To use binfmt in other projects:

Ensure you have run registration as above.
Copy the correct interpreter into the container in which you will run other-architecture commands. The COPY must be before any RUN command.

FROM calico/go-build:v0.16 as qemu

FROM arm64v8/golang:1.15.2-buster as base

# Enable non-native builds of this image on an amd64 hosts.
# This must be the first RUN command in this file!
# we only need this for the intermediate "base" image, so we can run all the apk and other commands
COPY --from=qemu /usr/bin/qemu-*-static /usr/bin/

# now we can do all our RUN commands
RUN apk --update add curl
# etc

Running a Binary

To run a binary from a different architecture, you need to use binfmt and qemu static.

docker run --rm --privileged multiarch/qemu-user-static:register

If a cross built binary is executed in the go-build container qemu-static will automatically be used.

Testing Cross-Run

There is a Makefile target that cross-builds and runs a binary. To run it on your own architecture:

make testcompile

make testcompile ARCH=$(uname -m)

To test on a different architecture, for example arm64 when you are running on amd64, pass it an alternate architecture:

make testcompile ARCH=arm64

You should see the "success" message.

robbrockbank/go-build