exit-strategy

Exit Strategy

• Generates error event handlers to gracefully kill your app
• Optimised for use with node's domains
• Uses visionmedia's logger to print POSIX error codes to STDOUT that will be picked up by logwatch

Full Example

var	app					= require('express').express(),
	domain				= require('domain'),
	appDomain			= domain.create(),
	exitStrategy		= require('exit-strategy'),
	exitAppDomain		= exitStrategy.app.exitAppDomain,
	exitServerDomain	= exitStrategy.server.exitServerDomain,
	exitApp				= exitAppDomain(app),
	server, exitServer;

// attach error handler
appDomain.on('error', exitApp);

// wrap app execution in domain to deal with uncaught exceptions
appDomain.run(function () {

	// 1. create http server
	server = server.listen(app.get('port'), function() {
		// you need to add this!
		app.set('serverListening', true);
	});

	// 2. replace exitApp with exitServer error handler once inited server
	exitServer = exitServerDomain(app, server);
	appDomain.on('error', exitServer).removeListener('error', exitApp);

	// 3. kill app for serious error evts you catch and broadcast with app.emit('seriousError')
	app.on('seriousError', exitServer);
	process.on('SIGTERM', exitServer);

	// 4. send 502s to new connections if started server shutdown process
	app.use(exitStrategy.middleware.closeGracefully(app));

	// define routes etc
});

Logwatch Setup

• by default logwatch watches all files in /var/log and subdirs
• make sure your app logs to a file in this dir
• logwatch will email you alerts depending upon the --detail level you set it to

API

.app.exitServerDomain(app, httpServer) returns -> fn (err)

• app needs get/set methods (see getter-setter module if you don't want to use express)
• returns error handler function (fn (err))

var app       	  = require('express').express(),
	appDomain	  = domain.create(),
	exitAppDomain = require('exit-strategy').app.exitAppDomain(app);

var server = server.listen(app.get('port'), function() {
	// you need to add this!
	app.set('serverListening', true);
});
appDomain.on('error', exitServerDomain(app, server));
appDomain.run(function () {
	// run your app - set up routes etc...
});

what the server domain error handler does:

1. checks if the server is active
2. calls server.close()
3. sets timer to kill app if server.close() takes more than 30s
4. calls exitApp
5. calls exitProcess

.app.exitAppDomain(app) returns -> fn (err)

• app needs get/set methods (see getter-setter module if you don't want to use express)

• returns error handler function (fn (err))

  var app             = require('express').express(),
      appDomain      = domain.create(),
      exitAppDomain = require('exit-strategy').app.exitAppDomain(app);
  
  appDomain.on('error', exitApp);
  appDomain.run(function () {
      // run your app
  });

what the app domain error handler does:

1. if app.get('serverListening') then lets serverDomain handle it
2. sets app flag

app.set('killingApp', true);

1. calls exitProcess

.exitProcess(app, err)

what it does:

1. logs error to STDOUT
2. exits process

.middleware.closeGracefully(app)

• Middleware to prevent new connections once the exit routine has been initiated.
• If you are load balancing then see this guide for configuring nginx to fail over to the next upstream server

var app = require('express').express(),

// send 502s to new connections if started server shutdown process
app.use(exitStrategy.middleware.closeGracefully(app));