[misc] Build the upload server from source, nonroot on Chainguard (#7663)

upload-server/Dockerfile only packaged the goreleaser-built binary, so
the image could not be built from a checkout.  It is now a multi-stage
build on Chainguard static, running as the nonroot user (uid 65532),
with a VARIANT=debug build arg that swaps in busybox for a shell.

The goreleaser packaging file moves unchanged to Dockerfile.release and
.goreleaser.yaml points at it, so the published netbirdio/upload image
stays as it was: distroless and root.

The bases are pinned by digest, since Chainguard publishes only :latest
for free.  A Dependabot docker entry for /upload-server moves them
weekly, leaving the release base alone and holding golang to patch
updates.

.github/dependabot.yml

@@ -46,3 +46,25 @@ updates:
       wireguard:
         patterns:
           - "golang.zx2c4.com/wireguard*"
+
+  # Base images of the source-build Dockerfiles, pinned by digest (Chainguard
+  # publishes only :latest for free). Dockerfile.release files feed goreleaser
+  # and keep the published images as they are, so their bases are left alone.
+  - package-ecosystem: "docker"
+    directories:
+      - "/upload-server"
+    schedule:
+      interval: "weekly"
+    open-pull-requests-limit: 3
+    groups:
+      base-images:
+        patterns:
+          - "*"
+    ignore:
+      - dependency-name: "gcr.io/distroless/base"
+      # Go minor and major versions move with the rest of the repository;
+      # patch releases and new digests of the pinned tag still come through.
+      - dependency-name: "golang"
+        update-types:
+          - "version-update:semver-minor"
+          - "version-update:semver-major"

.goreleaser.yaml

@@ -477,7 +477,7 @@ dockers_v2:
      tags:
        - "{{ .Version }}"
        - "{{ if eq .Env.SKIP_PUBLISH \"false\" }}latest{{ end }}"
-     dockerfile: upload-server/Dockerfile
+     dockerfile: upload-server/Dockerfile.release
      platforms:
        - linux/amd64
        - linux/arm64

upload-server/Dockerfile

@@ -1,4 +1,51 @@
-FROM gcr.io/distroless/base:debug
-ENTRYPOINT [ "/go/bin/netbird-upload" ]
-ARG TARGETPLATFORM
-COPY ${TARGETPLATFORM}/netbird-upload /go/bin/netbird-upload
+# syntax=docker/dockerfile:1
+
+# Builds the upload server from source. Run it from the repository root:
+#
+#   docker build -f upload-server/Dockerfile .
+#
+# Releases package the goreleaser-built binary with Dockerfile.release instead,
+# which keeps the published image as it was (distroless base, running as root).
+#
+# The image runs as the base image's nonroot user (uid 65532), which owns the
+# default STORE_DIR, /var/lib/netbird. A volume mounted there must be writable
+# by that uid: a named Docker volume takes the directory's ownership on first
+# use, a bind mount needs chown, and Kubernetes needs fsGroup: 65532.
+#
+# Build args:
+#   VARIANT=release|debug  debug swaps the base for Chainguard busybox (a shell)
+#   VERSION                stamped into the binary the same way goreleaser does
+#
+# Chainguard publishes only :latest for free, so the bases are pinned by digest
+# and moved by Dependabot.
+
+ARG VARIANT=release
+
+# Pure Go: cross-compile from the build host instead of emulating the target.
+FROM --platform=$BUILDPLATFORM golang:1.26.7-bookworm@sha256:e8c859f5632dcfde7b32d2012b4351728f6437930887c2f6a91ea242459e5514 AS builder
+WORKDIR /app
+
+COPY go.mod go.sum ./
+RUN --mount=type=cache,target=/go/pkg/mod go mod download
+
+COPY . .
+ARG TARGETOS
+ARG TARGETARCH
+ARG VERSION=development
+RUN --mount=type=cache,target=/go/pkg/mod \
+    --mount=type=cache,target=/root/.cache/go-build \
+    CGO_ENABLED=0 GOOS=${TARGETOS} GOARCH=${TARGETARCH} go build -trimpath \
+      -ldflags "-s -w -X github.com/netbirdio/netbird/version.version=${VERSION}" \
+      -o /out/netbird-upload ./upload-server \
+    && mkdir -p /out/var/lib/netbird
+
+FROM cgr.dev/chainguard/static:latest@sha256:41e17ed83c594a64a9396b6ab96dd26d5ddc290dacf4c177464712ff21ad534f AS base-release
+FROM cgr.dev/chainguard/busybox:latest@sha256:b2953ab1cae4a6265e18cf675851bd99975211b150d7a014774911d76eb309ba AS base-debug
+
+# hadolint ignore=DL3006
+FROM base-${VARIANT}
+COPY --from=builder --chown=65532:65532 /out/var/lib/netbird /var/lib/netbird
+COPY --from=builder /out/netbird-upload /go/bin/netbird-upload
+WORKDIR /var/lib/netbird
+USER 65532:65532
+ENTRYPOINT ["/go/bin/netbird-upload"]

upload-server/Dockerfile.release

@@ -0,0 +1,4 @@
+FROM gcr.io/distroless/base:debug
+ENTRYPOINT [ "/go/bin/netbird-upload" ]
+ARG TARGETPLATFORM
+COPY ${TARGETPLATFORM}/netbird-upload /go/bin/netbird-upload