daemonize3 v1.0.2

daemonize3

daemonize3 is a NodeJS module, which lets one turn a normal node application (app) into a daemon easily, so that it detaches from the controlling terminal and continues to in the background. Furthermore if needed, one may even run it in the foreground by just setting the corresponding option, which makes troubleshooting much easier (e.g. if the app doesn't start properly).

The 'Runner' does this by spawning a wrapper, which in turn just runs the given app (more or less like require("app.js")) and redirects per default its output to /dev/null, however, it can be configured to redirect its stdout and/or stderr to a stream of your choice by just setting the appropriate option(s). Also the wrapper feeds information about the clients state back to its 'Runner', so that it knows, that the client is actually running (or not) and can exit with the exit code obtained via wrapper's feedback and thus e.g. follows the simple fork-exec-model prefered by the Solaris service management facilities (SMF).

Dueto the async nature of most apps the wrapper can't really tell from its perspective, whether the app is finally runnning or still in its "starting/configure" phase. The app may help it by just emmitting a 'daemon_running' event (optional with a short info message attached), e.g. when the app's http listener actually started listening for http requests. If it doesn't do it, a timer fires this event after the configured period of time. On this event the wrapper sends the corresponding notification incl. the process.exitCode currently set to its runner and closes all additional communication channels, removes related listeners.

To customize the wrappers start as needed, the following options are supported:

Example

application.js (the main application as is):

var port = process.argv[2] || 3000;
var server = require('http').createServer((req, res) => {
	res.writeHead(200, {'Content-Type': 'text/plain'});
	res.end('okay');
});
server.on('error', function(e) {
	if (e.code == 'EADDRINUSE') {
		console.error('Unable to listen on port %d (port already in use)',port);
		process.exitCode = 95;
	} else if (e.code == 'EACCES') {
		console.error('Unable to listen on port %d (permission denied)',port);
		process.exitCode = 100;
	} else {
		console.error('An unexpected error occured (%s)', e.code);
		process.exitCode = 94;
	}
});
server.on('listening', function() {
	console.log('Listening on port ' + port);
	process.emit('daemon_running', 'Listening on port ' + port);
});
server.on('close', function() {
	console.log('Stopping service on port %d ...', port);
});
server.listen(port);

run.js (the little, trivial helper to run the daemon):

#!/usr/bin/env node

var arg = process.argv[2];
 
runner = new require('daemonize3').Runner({
	name: 'My http service',
	main: 'application.js',
	args: [ (!!arg) && arg.search(/^[0-9]+$/) != -1 ? arg : 52768 ],
	foreground: (!!arg) && typeof arg !== 'number'
});

if (arg == 'stop') {
	runner.stop();
} else {
	runner.startDaemon();
}

So you may try out the following commands to explore the example further:

• test start/stop run.js run.js stop

• force an error on the 2nd invocation run.js run.js * run.js stop

• force a permission denied error * run.js 80

• run the app not as a daemon * run.js fg

• last but not least, comment out the process.emit(....) line in application.js and watch out, what happens now (the timeout is used to draw the assumption, that the app is running, if no error occures).