Example of NodeJS which works with SystemD notify protocol

app.js

const { DgramSocket } = require("node-unix-socket");
const http = require("node:http");

/**
 * Implements notify mechanism for systemd services which created with systemd.
 *
 * See all kinds of messages which can be sent to systemd
 * https://man.archlinux.org/man/sd_notify.3.en#WELL-KNOWN_ASSIGNMENTS
 *
 * @param {string} message - The message to send
 * @returns {Promise<void>}
 */
const sdNotify = async message => {
  const notifySocket = process.env.NOTIFY_SOCKET;
  if (!notifySocket) {
    return;
  }

  if (!message?.trim()) {
    return;
  }

  return new Promise((resolve, reject) => {
    const socket = new DgramSocket();
    const buffer = Buffer.from(message);
    socket.sendTo(
      buffer,
      0,
      buffer.length,
      notifySocket,
      (/** @type {Error | undefined} */ cause) => {
        if (cause) {
          reject(new Error("Failed to send systemd notify: " + message, { cause }));
        } else {
          resolve(undefined);
        }
      }
    );
  });
};

sdNotify("STATUS=Starting");
sdNotify("MAINPID=" + process.pid);

const server = http.createServer(function (req, res) {
  res.writeHead(200, {
    "Content-Type": "text/plain"
  });
  res.end("OK");
});

const main = async () => {
  await sdNotify("READY=1");
  await sdNotify("STATUS=Running");
  server.listen(process.env.PORT ? parseInt(process.env.PORT, 10) : 8080);
}

process.on("SIGINT", async () => {
  await sdNotify("STOPPING=1");
  server.close();
  process.exit(1);
});

process.on("SIGTERM", async () => {
  await sdNotify("STOPPING=1");
  server.close();
  process.exit(0);
});

main();

app.service

[Unit]
Description=App
After=network.target
# Limit 5 restarts
StartLimitIntervalSec=1h
StartLimitBurst=5

[Service]
Type=notify
WorkingDirectory=/home/ubuntu/app
ExecStart=/usr/bin/env node app.js
Restart=always
RestartSec=10
StandardOutput=journal
StandardError=journal
SyslogIdentifier=app

package.json

{
  "name": "app",
  "version": "0.1.1",
  "license": "MIT",
  "private": false,
  "repository": "https://gist.github.com/huksley/f083691cb061ca50013bff5f1753934a/",
  "main": "app.js",
  "dependencies": {
    "node-unix-socket": "^0.2.7"
  }
}

sudo cp app.service /etc/systemd/system/app.service
sudo systemctl daemon-reload
sudo systemctl reset-failed app
sudo systemctl start app
sudo systemctl restart app
sudo systemctl status app