[BUG] k3d-managed registry with non-5000 port not accessible from within the cluster

[yashgorana]

What did you do

How was the cluster created?

$ k3d registry create registry.localhost --port 12345
$ k3d cluster create test-cluster --registry-use k3d-registry.localhost:12345

What did you do afterwards?

Tried to access the registry k3d-registry.localhost:12345 from a pod in the k3d cluster

$ kubectl run -i --rm --tty busybox --image=busybox --restart=Never -- sh
/ # wget -qO- http://k3d-registry.localhost:12345/v2/_catalog
wget: can't connect to remote host (172.19.0.2): Connection refused

What did you expect to happen

Since registry is exposed on :12345, and k3d injects this domain in coredns' NodeHosts, http://k3d-registry.localhost:12345/ should be accessible from within the cluster. Instead k3d-registry.localhost:5000 is accessible. I don't want to use host.k3d.internal:12345 as it requires us to tweak the domains at application layer, which isn't ideal.

If we map k3d-registry.localhost to host system's IP (like we do for host.k3d.internal), instead of the registry IP, then the above works as expected.

Screenshots or terminal output

Which OS & Architecture

Debian on WSL2

arch: x86_64
cgroupdriver: cgroupfs
cgroupversion: "1"
endpoint: /var/run/docker.sock
filesystem: extfs
infoname: docker-desktop
name: docker
os: Docker Desktop
ostype: linux
version: 25.0.1

Which version of k3d

k3d version v5.6.0
k3s version v1.27.4-k3s1 (default)

Which version of docker

Client:
 Cloud integration: v1.0.35+desktop.10
 Version:           25.0.1
 API version:       1.44
 Go version:        go1.21.6
 Git commit:        29cf629
 Built:             Tue Jan 23 23:08:30 2024
 OS/Arch:           linux/amd64
 Context:           default

Server: Docker Desktop
 Engine:
  Version:          25.0.1
  API version:      1.44 (minimum version 1.24)
  Go version:       go1.21.6
  Git commit:       71fa3ab
  Built:            Tue Jan 23 23:09:46 2024
  OS/Arch:          linux/amd64
  Experimental:     false
 containerd:
  Version:          1.6.27
  GitCommit:        a1496014c916f9e62104b33d1bb5bd03b0858e59
 runc:
  Version:          1.1.11
  GitCommit:        v1.1.11-0-g4bccb38
 docker-init:
  Version:          0.19.0
  GitCommit:        de40ad0

Client:
 Version:    25.0.1
 Context:    default
 Debug Mode: false
 Plugins:
  buildx: Docker Buildx (Docker Inc.)
    Version:  v0.12.1-desktop.4
    Path:     /usr/local/lib/docker/cli-plugins/docker-buildx
  compose: Docker Compose (Docker Inc.)
    Version:  v2.24.3-desktop.1
    Path:     /usr/local/lib/docker/cli-plugins/docker-compose
  debug: Get a shell into any image or container. (Docker Inc.)
    Version:  0.0.22
    Path:     /usr/local/lib/docker/cli-plugins/docker-debug
  dev: Docker Dev Environments (Docker Inc.)
    Version:  v0.1.0
    Path:     /usr/local/lib/docker/cli-plugins/docker-dev
  extension: Manages Docker extensions (Docker Inc.)
    Version:  v0.2.21
    Path:     /usr/local/lib/docker/cli-plugins/docker-extension
  feedback: Provide feedback, right in your terminal! (Docker Inc.)
    Version:  v1.0.4
    Path:     /usr/local/lib/docker/cli-plugins/docker-feedback
  init: Creates Docker-related starter files for your project (Docker Inc.)
    Version:  v1.0.0
    Path:     /usr/local/lib/docker/cli-plugins/docker-init
  sbom: View the packaged-based Software Bill Of Materials (SBOM) for an image (Anchore Inc.)
    Version:  0.6.0
    Path:     /usr/local/lib/docker/cli-plugins/docker-sbom
  scout: Docker Scout (Docker Inc.)
    Version:  v1.3.0
    Path:     /usr/local/lib/docker/cli-plugins/docker-scout
WARNING: Plugin "/usr/local/lib/docker/cli-plugins/docker-scan" is not valid: failed to fetch metadata: fork/exec /usr/local/lib/docker/cli-plugins/docker-scan: no such file or directory

Server:
 Containers: 0
  Running: 0
  Paused: 0
  Stopped: 0
 Images: 13
 Server Version: 25.0.1
 Storage Driver: overlay2
  Backing Filesystem: extfs
  Supports d_type: true
  Using metacopy: false
  Native Overlay Diff: true
  userxattr: false
 Logging Driver: json-file
 Cgroup Driver: cgroupfs
 Cgroup Version: 1
 Plugins:
  Volume: local
  Network: bridge host ipvlan macvlan null overlay
  Log: awslogs fluentd gcplogs gelf journald json-file local splunk syslog
 Swarm: inactive
 Runtimes: io.containerd.runc.v2 runc
 Default Runtime: runc
 Init Binary: docker-init
 containerd version: a1496014c916f9e62104b33d1bb5bd03b0858e59
 runc version: v1.1.11-0-g4bccb38
 init version: de40ad0
 Security Options:
  seccomp
   Profile: unconfined
 Kernel Version: 5.15.133.1-microsoft-standard-WSL2
 Operating System: Docker Desktop
 OSType: linux
 Architecture: x86_64
 CPUs: 28
 Total Memory: 15.5GiB
 Name: docker-desktop
 ID: a849da8e-3fd3-4c5f-9422-bdce4b1a7bae
 Docker Root Dir: /var/lib/docker
 Debug Mode: false
 HTTP Proxy: http.docker.internal:3128
 HTTPS Proxy: http.docker.internal:3128
 No Proxy: hubproxy.docker.internal
 Experimental: false
 Insecure Registries:
  hubproxy.docker.internal:5555
  127.0.0.0/8
 Live Restore Enabled: false