Connection refused error when pushing to a local registry

[ixfg9922]

I have a trivially simple Dockerfile (of only "FROM ubuntu:24.04") and I'm trying to build with buildx and push to a local registry as here:

~/local/testbuildxpush/: docker buildx build -t localhost:5000/test:1 --push .
[+] Building 1.6s (6/6) FINISHED                                                                                                                                                  
 => [internal] load build definition from Dockerfile                                                                                                                         0.0s
 => => transferring dockerfile: 113B                                                                                                                                         0.0s
 => [internal] load metadata for docker.io/library/ubuntu:24.04                                                                                                              1.5s
 => [auth] library/ubuntu:pull token for registry-1.docker.io                                                                                                                0.0s
 => [internal] load .dockerignore                                                                                                                                            0.0s
 => => transferring context: 2B                                                                                                                                              0.0s
 => CACHED [1/1] FROM docker.io/library/ubuntu:24.04@sha256:3f85b7caad41a95462cf5b787d8a04604c8262cdcdf9a472b8c52ef83375fe15                                                 0.0s
 => => resolve docker.io/library/ubuntu:24.04@sha256:3f85b7caad41a95462cf5b787d8a04604c8262cdcdf9a472b8c52ef83375fe15                                                        0.0s
 => ERROR exporting to image                                                                                                                                                 0.0s
 => => exporting layers                                                                                                                                                      0.0s
 => => exporting manifest sha256:139a9f8800dd4fb029fbd937bd1653e2094ab3e0a235deab32ed9d21c981df44                                                                            0.0s
 => => exporting config sha256:eef40204959e40e2ce01b660edf76bdaff7e3ed60137e53a43e0c5f19e593364                                                                              0.0s
 => => exporting attestation manifest sha256:202fe16d488c421de76513659782857a1f18bf9d4ebad2684dda97b9ced32010                                                                0.0s
 => => exporting manifest list sha256:6838fea794b972da3e8db261d545c22c52285ea9f90f1cbbe5c2703e60bad637                                                                       0.0s
 => => pushing layers                                                                                                                                                        0.0s
------
 > exporting to image:
------
ERROR: failed to solve: failed to push localhost:5000/test:1: failed to do request: Head "http://localhost:5000/v2/test/blobs/sha256:eef40204959e40e2ce01b660edf76bdaff7e3ed60137e53a43e0c5f19e593364": dial tcp 127.0.0.1:5000: connect: connection refused

However, I'm continually geting the "connection refused" error shown.

At the same time, the local registry container is up:

~/local/testbuildxpush/: docker ps
CONTAINER ID   IMAGE                           COMMAND                  CREATED         STATUS         PORTS     NAMES
d0e25bdc10a0   registry:2                      "/entrypoint.sh /etc…"   3 minutes ago   Up 3 minutes             registry
c91c35ed0445   moby/buildkit:buildx-stable-1   "buildkitd"              2 hours ago     Up 2 hours               buildx_buildkit_mybuilder0

and seems to be working:

~/local/testbuildxpush/: docker tag moby/buildkit:buildx-stable-1 localhost:5000/buildkit:1
~/local/testbuildxpush/: docker push localhost:5000/buildkit:1
The push refers to repository [localhost:5000/buildkit]
d838ca4e7718: Pushed 
f5bc6b547867: Pushed 
7da13a3469bd: Pushed 
d4fc045c9e3a: Pushed 
1: digest: sha256:c3cb08891c15763d426ba017fa7ce957537a779837f5bf2f7b50de3796e13918 size: 1158

I've tried to start the registry container in several ways in order to avoid this problem. In the above case, I started it with simply

docker run -d --name registry --network=host registry:2

but I've also tried it several other ways, choosing different network options and specifying the ports, and I keep getting the same error.

Does this error make sense to anyone? At the moment, I don't see what I'm doing wrong here.