[Request]: Consider Exposing buildkit daemon In Order To Register As A Remote Builder

[vkhitrin]

Feature or enhancement request details

Hey,

I am not sure if this request is in the scope of this project or the direction of the shim.

The use case I had in mind is (if approved and matches the direction of the project) to offer an additional flag which will expose the buildkit socket directly via TCP or socket.
This will allow buildkit compatible clients to register and use this builder.

Small demo:

1. Create a custom builder container with a custom wrapper script that starts buildkitd.
   For demonstration purposes I created the script on the host at ${HOME}/Library/Application Support/com.apple.container/builder which is already mounted by default:

   $ ps
   PID   USER     TIME  COMMAND
       1 root      0:00 /usr/local/bin/container-builder-shim --debug --vsock --buildkitd-path /var/lib/container-builder-shim/exports/buildkitd-wrapper.sh
      10 root      0:00 /usr/bin/buildkitd --addr unix:///run/buildkit/buildkitd.sock --addr tcp://0.0.0.0:18088
   $ cat /var/lib/container-builder-shim/exports/buildkitd-wrapper.sh
   #!/bin/sh
   exec /usr/bin/buildkitd --addr unix:///run/buildkit/buildkitd.sock --addr tcp://0.0.0.0:18088 "$@"

2. Register the builder and verify it is responding:

   $ docker buildx create --name socktainer-remote --driver remote tcp://192.168.64.4:18088 --use
   socktainer-remote
   $ docker buildx inspect socktainer-remote --bootstrap
   Name:          socktainer-remote
   Driver:        remote
   Last Activity: 2026-04-11 15:23:22 +0000 UTC
   
   Nodes:
   Name:             socktainer-remote0
   Endpoint:         tcp://192.168.64.9:18088
   Status:           running
   BuildKit version: v0.26.2
   Platforms:        linux/arm64
   Labels:
    org.mobyproject.buildkit.worker.executor:         oci
    org.mobyproject.buildkit.worker.hostname:         buildkit
    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
   GC Policy rule#0:
    All:            false
    Filters:        type==source.local,type==exec.cachemount,type==source.git.checkout
    Keep Duration:  48h0m0s
    Max Used Space: 488.3MiB
   GC Policy rule#1:
    All:            false
    Keep Duration:  1440h0m0s
    Reserved Space: 32GiB
   GC Policy rule#2:
    All:            false
    Reserved Space: 32GiB
   GC Policy rule#3:
    All:            true
    Reserved Space: 32GiB

3. Initiate a build using docker CLI:

   docker build . -t test --builder socktainer-remote --load
   [+] Building 0.8s (12/12) FINISHED                                                                                                   remote:socktainer-remote
    => [internal] load build definition from Dockerfile                                                                                                     0.0s
    => => transferring dockerfile: 391B                                                                                                                     0.0s
    => [internal] load metadata for docker.io/library/alpine:3                                                                                              0.2s
    => [internal] load .dockerignore                                                                                                                        0.0s
    => => transferring context: 2B                                                                                                                          0.0s
    => [internal] load build context                                                                                                                        0.0s
    => => transferring context: 338B                                                                                                                        0.0s
    => [1/6] FROM docker.io/library/alpine:3@sha256:25109184c71bdad752c8312a8623239686a9a2071e8825f20acb8f2198c3f659                                        0.0s
    => => resolve docker.io/library/alpine:3@sha256:25109184c71bdad752c8312a8623239686a9a2071e8825f20acb8f2198c3f659                                        0.0s
    => CACHED [2/6] COPY config/config.yaml /app/config/config.yaml                                                                                         0.0s
    => CACHED [3/6] COPY build/linux/arm64/ /usr/local/bin/                                                                                                 0.0s
    => CACHED [4/6] COPY entrypoint.sh /app/entrypoint.sh                                                                                                   0.0s
    => CACHED [5/6] RUN chmod +x /app/entrypoint.sh                                                                                                         0.0s
    => CACHED [6/6] WORKDIR /app                                                                                                                            0.0s
    => exporting to docker image format                                                                                                                     0.5s
    => => exporting layers                                                                                                                                  0.0s
    => => exporting manifest sha256:02a58a4526c76d50143b7a1c5aa030c57844b9b937d028d965c32b6cce93a105                                                        0.0s
    => => exporting config sha256:8dd7bc2b70e64bca774f3b82fd4045f96ee57e38b6c486e71998c133dc8fb4b1                                                          0.0s
    => => sending tarball                                                                                                                                   0.5s
    => importing to docker

4. Verify image:

   $ container image ls
   NAME           TAG              DIGEST
   test           latest           9f1611b0f9a4c957b98d596f...

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