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terminus

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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 { createTerminus } = 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 ({ state }) {
  // `state.isShuttingDown` (boolean) shows whether the server is shutting down or not
  return Promise.resolve(
    // optionally include a resolve value to be included as
    // info in the health check response
  )
}

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

const options = {
  // health check options
  healthChecks: {
    '/healthcheck': healthCheck,    // a function accepting a state and returning a promise indicating service health,
    verbatim: true,                 // [optional = false] use object returned from /healthcheck verbatim in response,
    __unsafeExposeStackTraces: true // [optional = false] return stack traces in error response if healthchecks throw errors
  },
  caseInsensitive,                  // [optional] whether given health checks routes are case insensitive (defaults to false)

  statusOk,                         // [optional = 200] status to be returned for successful healthchecks
  statusOkResponse,                 // [optional = { status: 'ok' }] status response to be returned for successful healthchecks
  statusError,                      // [optional = 503] status to be returned for unsuccessful healthchecks
  statusErrorResponse,              // [optional = { status: 'error' }] status response to be returned for unsuccessful healthchecks

  // cleanup options
  timeout: 1000,                    // [optional = 1000] number of milliseconds before forceful exiting
  signal,                           // [optional = 'SIGTERM'] what signal to listen for relative to shutdown
  signals,                          // [optional = []] array of signals to listen for relative to shutdown
  useExit0,                         // [optional = false] instead of sending the received signal again without beeing catched, the process will exit(0)
  sendFailuresDuringShutdown,       // [optional = true] whether or not to send failure (503) during 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
  onSendFailureDuringShutdown,      // [optional] called before sending each 503 during shutdowns

  // both
  logger                            // [optional] logger function to be called with errors. Example logger call: ('error happened during shutdown', error). See terminus.js for more details.
};

createTerminus(server, options);

server.listen(PORT || 3000);

With custom error messages

const http = require('http');
const { createTerminus, HealthCheckError } = require('@godaddy/terminus');

createTerminus(server, {
  healthChecks: {
    '/healthcheck': async function () {
      const errors = []
      return Promise.all([
        // all your health checks goes here
      ].map(p => p.catch((error) => {
        // silently collecting all the errors
        errors.push(error)
        return undefined
      }))).then(() => {
        if (errors.length) {
          throw new HealthCheckError('healthcheck failed', errors)
        }
      })
    }
  }
});

With custom headers

const http = require("http");
const express = require("express");
const { createTerminus, HealthCheckError } = require('@godaddy/terminus');
const app = express();

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

const server = http.createServer(app);

function healthCheck({ state }) {
  return Promise.resolve();
}

const options = {
  healthChecks: {
    "/healthcheck": healthCheck,
    verbatim: true,
    __unsafeExposeStackTraces: true,
  },
  headers: {
    "Access-Control-Allow-Origin": "*",
    "Access-Control-Allow-Methods": "OPTIONS, POST, GET",
  },
};

terminus.createTerminus(server, options);

server.listen(3000);

With express

const http = require('http');
const express = require('express');
const { createTerminus } = require('@godaddy/terminus');
const app = express();

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

const server = http.createServer(app);

const options = {
  // opts
};

createTerminus(server, options);

server.listen(PORT || 3000);

With koa

const http = require('http');
const Koa = require('koa');
const { createTerminus } = require('@godaddy/terminus');
const app = new Koa();

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

const options = {
  // opts
};

createTerminus(server, options);

server.listen(PORT || 3000);

With cluster (and eg. express)

If you want to use (cluster)[https://nodejs.org/api/cluster.html] to use more than one CPU, you need to use terminus per worker. This is heavily inspired by https://medium.com/@gaurav.lahoti/graceful-shutdown-of-node-js-workers-dd58bbff9e30.

See example/express.cluster.js.

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.

Also it makes sense to use the useExit0 = true option to signal Kubernetes that the container exited gracefully. Otherwise APM's will send you alerts, in some cases.

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)
  })
}
createTerminus(server, {
  beforeShutdown,
  useExit0: true
})

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.