feat: add ARM64 support and multi-arch build for Raspberry Pi and other ARM devices

[andrewiankidd]

Hi,

I'm aware this repo has been inactive for a while, but I've been using it regularly and recently tried to run it on my Raspberry Pi cluster — that’s when I found Issue #34.
This PR implements the changes needed to make that possible.

Summary of changes

• Adds GitHub workflow for multi-arch builds (amd64 + arm64)
• Completes Alpine base compatibility
• Minor entrypoint adjustments to support Alpine and ARM environments
• Adds automatic disabling of NFSv2 when the kernel only exposes v3/v4

The resulting image is available at:
👉 https://hub.docker.com/r/andrewkidd/nfs-server/tags (v2.2.5)

Evidence running on Raspberry Pi 5 (ARM64 / Ubuntu 24.04 / k3s)

# Image name
root@valar-50:/home/ubuntu# kubectl get pod nfs-5f47bb585b-7r6vf -n ainur-netboot \
  -o jsonpath='{.spec.containers[0].image}'
andrewkidd/nfs-server:v2.2.5
# Pod info
root@valar-50:/home/ubuntu# kubectl exec -it -n ainur-netboot nfs-5f47bb585b-7r6vf -- /bin/sh
Defaulted container "nfs" out of: nfs, load-nfsd (init)
/ # uname -a
Linux nfs-5f47bb585b-7r6vf 6.8.0-1031-raspi #35-Ubuntu SMP PREEMPT_DYNAMIC Thu Jul  3 15:00:20 UTC 2025 aarch64 Linux
/ # cat /etc/os-release | grep PRETTY_NAME
PRETTY_NAME="Alpine Linux v3.22"
/ # exportfs -v
/mnt/nfsshare   <world>(async,wdelay,hide,no_subtree_check,insecure_locks,fsid=0,sec=sys,rw,insecure,no_root_squash,no_all_squash)
/ #

manifests

$ docker manifest inspect andrewkidd/nfs-server:v2.2.5 
{
   "schemaVersion": 2,
   "mediaType": "application/vnd.docker.distribution.manifest.list.v2+json",
   "manifests": [
      {
         "mediaType": "application/vnd.docker.distribution.manifest.v2+json",
         "size": 1091,
         "digest": "sha256:63e143eba7c00ced4d58990b23d5152f1ae05e7e8f7ccfbe5155fb0e9035bbb8",
         "platform": {
            "architecture": "amd64",
            "os": "linux"
         }
      },
      {
         "mediaType": "application/vnd.docker.distribution.manifest.v2+json",
         "size": 1091,
         "digest": "sha256:30ced108af00e6dbba208390147b3c5dc5de9c49e1ffeddad0d6be8ccb8f1ec8",
         "platform": {
            "architecture": "arm64",
            "os": "linux"
         }
      }
   ]
}