Feature/prometheus npm quadlet (#15)

* Stage Prometheus NPM Quadlet with backup-safe cutover

* Complete Prometheus NPM Quadlet cutover

scripts/cutover_prometheus_npm_quadlet.sh

@@ -0,0 +1,106 @@
+#!/usr/bin/env bash
+# Run on Prometheus as root with the exact verified source-export version.
+set -Eeuo pipefail
+
+expected_export=${1:?Pass the verified Prometheus backup export version}
+mode=${2:---preflight}
+[[ $expected_export =~ ^[0-9]{8}T[0-9]{6}Z$ ]] || exit 2
+[[ $mode == --preflight || $mode == --execute ]] || exit 2
+[[ $EUID -eq 0 ]] || { echo 'Run as root on Prometheus' >&2; exit 2; }
+
+compose_unit=podman-compose-server.service
+quadlet_unit=prometheus-npm.service
+backup_timer=prometheus-backup-export.timer
+versions=/var/lib/prometheus-backup-export/versions
+quadlet_file=/etc/containers/systemd/prometheus-npm.container
+
+exec 9>/run/lock/prometheus-backup-export.lock
+flock -n 9 || { echo 'Backup/export lock is busy' >&2; exit 1; }
+
+systemctl is-active --quiet "$compose_unit"
+if systemctl is-active --quiet "$quadlet_unit"; then
+  echo 'NPM Quadlet is already active; refusing overlapping cutover' >&2
+  exit 1
+fi
+[[ $(systemctl show "$quadlet_unit" -p LoadState --value) == loaded ]]
+[[ $(systemctl is-enabled "$compose_unit") == enabled ]]
+[[ $(readlink "$versions/current") == "$expected_export" ]]
+image=$(sed -n 's/^Image=//p' "$quadlet_file")
+[[ $image =~ ^docker\.io/jc21/nginx-proxy-manager@sha256:[a-f0-9]{64}$ ]]
+podman image exists "$image"
+(cd "$versions/current" && sha256sum -c payload.sha256 && tar -tf payload.tar >/dev/null)
+curl -fsS --connect-timeout 2 --max-time 5 -o /dev/null http://127.0.0.1:81/
+old_image=$(podman inspect nginx-proxy-manager --format '{{.Image}}')
+
+data_signature() {
+  python3 - <<'PY'
+import hashlib, os, sqlite3
+db = sqlite3.connect('file:/opt/npm/data/database.sqlite?mode=ro', uri=True)
+assert db.execute('pragma quick_check').fetchone()[0] == 'ok'
+counts = [db.execute('select count(*) from ' + table).fetchone()[0]
+          for table in ('proxy_host', 'certificate', 'user')]
+db.close()
+digest = hashlib.sha256()
+for root, dirs, files in os.walk('/opt/npm/letsencrypt'):
+    dirs.sort()
+    for name in sorted(files):
+        path = os.path.join(root, name)
+        with open(path, 'rb') as stream:
+            digest.update(path.encode() + b'\0' + stream.read())
+print(*counts, digest.hexdigest())
+PY
+}
+before=$(data_signature)
+if [[ $mode == --preflight ]]; then
+  echo 'NPM Quadlet cutover preflight passed; no service was changed'
+  exit 0
+fi
+
+stopped_old=false
+rollback() {
+  rc=$?
+  trap - EXIT
+  if (( rc != 0 )) && "$stopped_old"; then
+    echo 'NPM Quadlet cutover failed; restoring Compose' >&2
+    systemctl stop "$quadlet_unit" || true
+    systemctl enable "$compose_unit" || true
+    systemctl start "$compose_unit" || true
+    systemctl start "$backup_timer" || true
+    curl -fsS --connect-timeout 2 --max-time 10 -o /dev/null http://127.0.0.1:81/ || true
+  fi
+  exit "$rc"
+}
+trap rollback EXIT
+
+stopped_old=true
+systemctl stop "$backup_timer"
+systemctl stop "$compose_unit"
+if podman container exists nginx-proxy-manager; then
+  echo 'Compose left the NPM container behind; refusing duplicate ownership' >&2
+  exit 1
+fi
+systemctl disable "$compose_unit"
+systemctl start "$quadlet_unit"
+
+ready=false
+for _ in {1..60}; do
+  if curl -fsS --connect-timeout 2 --max-time 3 -o /dev/null http://127.0.0.1:81/; then
+    ready=true
+    break
+  fi
+  sleep 2
+done
+"$ready"
+systemctl is-active --quiet "$quadlet_unit"
+[[ $(podman inspect nginx-proxy-manager --format '{{.Image}}') == "$old_image" ]]
+podman exec nginx-proxy-manager nginx -t
+[[ $(data_signature) == "$before" ]]
+for hostname in git.fscotto.duckdns.org syncthing.fscotto.duckdns.org; do
+  status=$(curl -ksS --connect-timeout 3 --max-time 10 \
+    --resolve "$hostname:443:127.0.0.1" -o /dev/null -w '%{http_code}' \
+    "https://$hostname/")
+  [[ $status == 200 ]]
+done
+systemctl start "$backup_timer"
+stopped_old=false
+echo 'NPM Quadlet cutover passed local application and data checks'