CDI

CDI (Container Device Interface) provides a standard mechanism for device vendors to describe what is required to provide access to a specific resource such as a GPU beyond a simple device name.

Since BuildKit 0.20.0, you can access devices using the CDI interface. This allows you to use devices like GPUs in your builds.

[!NOTE] CDI support is yet to be tested on Windows.

Usage

To use CDI with BuildKit, you need to create the CDI configuration file for your device (either JSON or YAML) and put it in one of the following locations:

/etc/cdi
/var/run/cdi
/etc/buildkit/cdi

[!NOTE] Location can be changed by setting the specDirs option in the cdi section of the buildkitd.toml configuration file.

Let's create a simple CDI configuration file that injects an environment variable into the build environment and write it to /etc/cdi/foo.yml:

yaml

cdiVersion: "0.6.0"
kind: "vendor1.com/device"
devices:
- name: foo
  containerEdits:
    env:
    - FOO=injected

Start BuildKit and check the list of available devices for the default worker:

bash

buildctl debug workers -v

Platforms:      linux/amd64,linux/amd64/v2,linux/amd64/v3,linux/arm64,linux/riscv64,linux/ppc64le,linux/s390x,linux/386,linux/arm/v7,linux/arm/v6
BuildKit:       github.com/moby/buildkit v0.19.0-rc3-72-gb89ee491b.m b89ee491bc1c40b8533f098dab18e414c8b70885.m
Labels:
        org.mobyproject.buildkit.worker.executor:               oci
        org.mobyproject.buildkit.worker.hostname:               cc39352c87dd
        org.mobyproject.buildkit.worker.network:                host
        org.mobyproject.buildkit.worker.oci.process-mode:       sandbox
        org.mobyproject.buildkit.worker.selinux.enabled:        false
        org.mobyproject.buildkit.worker.snapshotter:            overlayfs
Devices:
        Name:           vendor1.com/device=foo
        AutoAllow:      true

GC Policy rule#0:
        All:                    false
        Filters:                type==source.local,type==exec.cachemount,type==source.git.checkout
        Keep duration:          48h0m0s
        Maximum used space:     512MB
GC Policy rule#1:
        All:                    false
        Keep duration:          1440h0m0s
        Reserved space:         10GB
        Minimum free space:     202GB
        Maximum used space:     100GB
GC Policy rule#2:
        All:                    false
        Reserved space:         10GB
        Minimum free space:     202GB
        Maximum used space:     100GB
GC Policy rule#3:
        All:                    true
        Reserved space:         10GB
        Minimum free space:     202GB
        Maximum used space:     100GB

Now let's create a Dockerfile to use this device:

dockerfile

FROM busybox
RUN --device=vendor1.com/device=foo \
  env|grep FOO

And check if the environment variable is injected during build:

bash

buildctl build --frontend=dockerfile.v0 --no-cache --local context=. --local dockerfile=.
#1 [internal] load build definition from Dockerfile
#1 transferring dockerfile: 99B done
#1 DONE 0.0s

#2 [internal] load metadata for docker.io/library/busybox:latest
#2 ...

#3 [auth] library/busybox:pull token for registry-1.docker.io
#3 DONE 0.0s

#2 [internal] load metadata for docker.io/library/busybox:latest
#2 DONE 0.8s

#4 [internal] load .dockerignore
#4 transferring context: 2B done
#4 DONE 0.0s

#5 [1/2] FROM docker.io/library/busybox:latest@sha256:a5d0ce49aa801d475da48f8cb163c354ab95cab073cd3c138bd458fc8257fbf1
#5 resolve docker.io/library/busybox:latest@sha256:a5d0ce49aa801d475da48f8cb163c354ab95cab073cd3c138bd458fc8257fbf1 0.0s done
#5 CACHED

#6 [2/2] RUN --device=vendor1.com/device=foo   env|grep FOO
#6 0.062 FOO=injected
#6 DONE 0.1s