buildx: Build cannot export to registry on localhost

While setting up a local demo, I found that buildx is unable to access a registry server running on localhost. I can see that my registry server is listening on port 5000 with a curl command. This is with the docker-container driver, so I suspect that container is not using the host namespace and therefore cannot see any services running on localhost.

$ docker buildx build -f Dockerfile.buildx --target debug --platform linux/amd64,linux/arm64 -t localhost:5000/bmitch-public/golang-hello:buildx1 --output type=registry .
[+] Building 3.1s (24/24) FINISHED
 => [internal] load build definition from Dockerfile.buildx                                                                       0.4s
 => => transferring dockerfile: 39B                                                                                               0.0s
 => [internal] load .dockerignore                                                                                                 0.5s
 => => transferring context: 34B                                                                                                  0.0s
 => [linux/amd64 internal] load metadata for docker.io/library/debian:latest                                                      0.7s
 => [linux/amd64 internal] load metadata for docker.io/tonistiigi/xx:golang                                                       0.7s
 => [linux/amd64 internal] load metadata for docker.io/library/golang:1.12-alpine                                                 0.8s
 => [internal] load build context                                                                                                 0.2s
 => => transferring context: 105B                                                                                                 0.0s
 => [linux/amd64 debug 1/2] FROM docker.io/library/debian@sha256:118cf8f3557e1ea766c02f36f05f6ac3e63628427ea8965fb861be904ec35a6  0.0s
 => => resolve docker.io/library/debian@sha256:118cf8f3557e1ea766c02f36f05f6ac3e63628427ea8965fb861be904ec35a6f                   0.0s
 => [linux/amd64 xgo 1/1] FROM docker.io/tonistiigi/xx:golang@sha256:4703827f56e3964eda6ca07be85046d1dd533eb0ed464e549266c10a4cd  0.0s
 => => resolve docker.io/tonistiigi/xx:golang@sha256:4703827f56e3964eda6ca07be85046d1dd533eb0ed464e549266c10a4cd8a29f             0.0s
 => [linux/amd64 dev 1/6] FROM docker.io/library/golang:1.12-alpine@sha256:cee6f4b901543e8e3f20da3a4f7caac6ea643fd5a46201c3c2387  0.0s
 => => resolve docker.io/library/golang:1.12-alpine@sha256:cee6f4b901543e8e3f20da3a4f7caac6ea643fd5a46201c3c2387183a332d989       0.0s
 => CACHED [linux/amd64 dev 2/6] COPY --from=xgo / /                                                                              0.0s
 => CACHED [linux/amd64 dev 3/6] RUN apk add --no-cache git ca-certificates                                                       0.0s
 => CACHED [linux/amd64 dev 4/6] RUN adduser -D appuser                                                                           0.0s
 => CACHED [linux/amd64 dev 5/6] WORKDIR /src                                                                                     0.0s
 => CACHED [linux/amd64 dev 6/6] COPY . /src/                                                                                     0.0s
 => CACHED [linux/amd64 build 1/1] RUN CGO_ENABLED=0 go build -ldflags '-w -extldflags -static' -o app .                          0.0s
 => CACHED [linux/amd64 debug 2/2] COPY --from=build /src/app /app                                                                0.0s
 => CACHED [linux/amd64 dev 2/6] COPY --from=xgo / /                                                                              0.0s
 => CACHED [linux/amd64 dev 3/6] RUN apk add --no-cache git ca-certificates                                                       0.0s
 => CACHED [linux/amd64 dev 4/6] RUN adduser -D appuser                                                                           0.0s
 => CACHED [linux/amd64 dev 5/6] WORKDIR /src                                                                                     0.0s
 => CACHED [linux/amd64 dev 6/6] COPY . /src/                                                                                     0.0s
 => CACHED [linux/amd64 build 1/1] RUN CGO_ENABLED=0 go build -ldflags '-w -extldflags -static' -o app .                          0.0s
 => CACHED [linux/amd64 debug 2/2] COPY --from=build /src/app /app                                                                0.0s
 => ERROR exporting to image                                                                                                      1.4s
 => => exporting layers                                                                                                           0.1s
 => => exporting manifest sha256:fb7fb1aacd96dcd6c9a6d2654fb2a9cf7692c3ebfd4d15bd1dd397d38713a589                                 0.2s
 => => exporting config sha256:8c443cd193baf5e58914a1ad50d8311e25f7d9ac86772a6ab2df99ed7f4ef6f3                                   0.2s
 => => exporting manifest sha256:d63ec5c6531662c1185b1cc90755573a1bbc1b4754998181847598433fe30e5e                                 0.2s
 => => exporting config sha256:3838e43619611f78eedbc6604fedc3ab134f2beb4225d45d10bb37698603189e                                   0.2s
 => => exporting manifest list sha256:4c8694f90dda751d32ccbd9e48bdeba1042467f07bd0193378e254141e7464ec                            0.2s
 => => pushing layers                                                                                                             0.0s
------
 > exporting to image:
------
failed to solve: rpc error: code = Unknown desc = failed to do request: Head http://localhost:5000/v2/bmitch-public/golang-hello/blobs/sha256:8c443cd193baf5e58914a1ad50d8311e25f7d9ac86772a6ab2df99ed7f4ef6f3: dial tcp 127.0.0.1:5000: connect: connection refused

$ curl -sSLk https://localhost:5000/v2/
{"errors":[{"code":"UNAUTHORIZED","message":"authentication required","detail":null}]}

$ docker buildx ls
NAME/NODE     DRIVER/ENDPOINT             STATUS  PLATFORMS
new *         docker-container
  new0        unix:///var/run/docker.sock running linux/amd64
default       docker
  default     default                     running linux/amd64

Note this is a low priority issue for me, I’d much rather see #80 solved.