terminus

Adds graceful shutdown and Kubernetes readiness / liveness checks for any HTTP applications.

Installation

Install via npm:

$ npm i @godaddy/terminus --save

Usage

const http = require('http');
const terminus = require('@godaddy/terminus');

function onSignal () {
  console.log('server is starting cleanup');
  return Promise.all([
    // your clean logic, like closing database connections
  ]);
}

function onShutdown () {
  console.log('cleanup finished, server is shutting down');
}

function healthCheck () {
  return Promise.resolve(
    // optionally include a resolve value to be included as
    // info in the healthcheck response
  )
}

const server = http.createServer((request, response) => {
  response.end(
    `<html>
      <body>
        <h1>Hello, World!</h1>
       </body>
     </html>`
   );
})

const options = {
  // healtcheck options
  healthChecks: {
    '/healthcheck': healthCheck    // a promise returning function indicating service health
  },

  // cleanup options
  timeout: 1000,                   // [optional = 1000] number of milliseconds before forcefull exiting
  signal,                          // [optional = 'SIGTERM'] what signal to listen for relative to shutdown
  signals,                          // [optional = []] array of signals to listen for relative to shutdown
  beforeShutdown,                  // [optional] called before the HTTP server starts its shutdown
  onSignal,                        // [optional] cleanup function, returning a promise (used to be onSigterm)
  onShutdown,                      // [optional] called right before exiting

  // both
  logger                           // [optional] logger function to be called with errors
};

terminus(server, options);

server.listen(PORT || 3000);

With express

const http = require('http');
const app = express();

app.get('/', (req, res) => {
  res.send('ok');
});

const server = http.createServer(app);

const options = {
  // opts
};

terminus(server, options);

server.listen(PORT || 3000);

With koa

const http = require('http');
const Koa = require('koa');
const app = new Koa();

const server = http.createServer(app.callback());

const options = {
  // opts
};

terminus(server, options);

server.listen(PORT || 3000);

How to set Terminus up with Kubernetes?

When Kubernetes or a user deletes a Pod, Kubernetes will notify it and wait for gracePeriod seconds before killing it.

During that time window (30 seconds by default), the Pod is in the terminating state and will be removed from any Services by a controller. The Pod itself needs to catch the SIGTERM signal and start failing any readiness probes.

If the ingress controller you use route via the Service, it is not an issue for your case. At the time of this writing, we use the nginx ingress controller which routes traffic directly to the Pods.

During this time, it is possible that load-balancers (like the nginx ingress controller) don't remove the Pods "in time", and when the Pod dies, it kills live connections.

To make sure you don't lose any connections, we recommend delaying the shutdown with the number of milliseconds that's defined by the readiness probe in your deployment configuration. To help with this, terminus exposes an option called beforeShutdown that takes any Promise-returning function.

function beforeShutdown () {
  // given your readiness probes run every 5 second
  // may be worth using a bigger number so you won't
  // run into any race conditions
  return new Promise(resolve => {
    setTimeout(resolve, 5000)
  })
}
terminus(server, {
  beforeShutdown
})

Learn more

Limited Windows support

Due to inherent platform limitations, terminus has limited support for Windows. You can expect SIGINT to work, as well as SIGBREAK and to some extent SIGHUP. However SIGTERM will never work on Windows because killing a process in the task manager is unconditional, i.e., there's no way for an application to detect or prevent it. Here's some relevant documentation from libuv to learn more about what SIGINT, SIGBREAK etc. signify and what's supported on Windows - http://docs.libuv.org/en/v1.x/signal.html. Also, see https://nodejs.org/api/process.html#process_signal_events.