Initial implementation: dns-updater daemon

RFC2136 dynamic-DNS updater. Watches a records file (inotify) and new
interface addresses and pushes TSIG-signed updates to BIND per zone, sending
only the delta. Native miekg/dns (structured per-zone RCODEs), local status
API + facter fact, systemd unit, nfpm RPM, Woodpecker CI.

Replaces the puppet dns-update shell script; keeps the same records-file and
TSIG-key contract.

scripts/build-rpm.sh

@@ -0,0 +1,34 @@
+#!/usr/bin/env bash
+#
+# Package the (already built) dns-updater binary into an RPM with nfpm.
+# Usage: scripts/build-rpm.sh [version]   (version defaults to $CI_COMMIT_TAG)
+#
+set -euo pipefail
+
+ROOT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")/.." && pwd)"
+cd "${ROOT_DIR}"
+
+VERSION="${1:-${CI_COMMIT_TAG:-0.0.0-dev}}"
+VERSION="${VERSION#v}" # strip a leading v
+DIST="dist"
+
+if [ ! -f "${DIST}/dns-updater" ]; then
+  echo "ERROR: ${DIST}/dns-updater not found; run 'make build' first" >&2
+  exit 1
+fi
+
+export PACKAGE_NAME="dns-updater"
+export PACKAGE_VERSION="${VERSION}"
+export PACKAGE_RELEASE="1"
+export PACKAGE_ARCH="amd64"
+export PACKAGE_PLATFORM="linux"
+export PACKAGE_DESCRIPTION="RFC2136 dynamic-DNS updater daemon: watches a records file and network interfaces and pushes TSIG-signed updates to BIND, with a local status API for facter."
+export PACKAGE_MAINTAINER="Ben Vincent <ben@unkin.net>"
+export PACKAGE_HOMEPAGE="https://git.unkin.net/unkin/dns-updater"
+export PACKAGE_LICENSE="MIT"
+
+envsubst <packaging/nfpm.yaml >"${DIST}/nfpm.yaml"
+nfpm pkg --config "${DIST}/nfpm.yaml" --target "${DIST}" --packager rpm
+
+echo "Built:"
+ls -1 "${DIST}"/*.rpm