Bringing choas to order in your node.js app

BRINGING CHAOS TO ORDER
IN YOUR NODE.JS APP
DAN JENKINS
NIMBLE APE
https://nimblea.pe

WHO AM I?
DAN JENKINS
NODE.JS DEVELOPER / ARCHITECT
GOOGLE DEVELOPER EXPERT IN WEBRTC
LOVE LEGO & TECHNIC
GENERAL GEEK
FOUNDER OF NIMBLE APE LTD
❤ OPEN SOURCE
3

NODE.JS & I
STARTED WITH NODE.JS WHEN IT WAS A BABY - 0.4
BUILT MANY, MANY MICROSERVICES AND REST APIS WITH NODE
SPENTTHE PASTYEAR WORKING ON A PLATFORM CALLED RESPOKE - WEBRTC
8

FUNNY STORY…
9
H E L L O
my name is
Dan
G O O G L E I / O

WARNING…
SOME BAD PRACTICES ARE USED IN SOME OF THE EXAMPLES.
I KNOW YOU SHOULDN’T DO THESE THINGS.
BUT, ITS THE EASIEST WAYTO SHOW THE POINT IN THE SMALL CONFINES OF A
SLIDE DECK.
I PROMISE I KNOW WHAT I’M DOING…
10

NODE.JS APPS CAN GET
IN A REAL MESS…

WHO’S WRITTEN CODE LIKE THIS ?
12
createAdministrator: function (req, res) {
Administrators.create({some: data}, function cb(error, admin) {
if (error) {
console.error('Error creating Admin');
res.send(500)
return;
}
res.admin = admin;
doAnotherCall(res, function cb2(err2){
res.send(200, res.admin);
});
});
}

OR LIKE THIS
13
var http = require('http');
var uuid = require('uuid');
function respond(res) {
console.log('Got request with ID', res.id);
res.end('Response');
}
var server = http.createServer(function handleRequest(req, res){
res.id = uuid();
respond(res)
});
server.listen(8080, function(){
console.log("Server listening on: http://localhost:8080");
});

OR LIKE THIS
14
function doSomething(res, id) {
console.log('Do something with request with ID', id);
respond(res, id);
}
function respond(res, id) {
console.log('Responding to request with ID', id);
}
var id = uuid();
doSomething(res, id);
});
});

WHAT PROBLEM ARE WE
TRYING TO SOLVE?

PASSING DATA AROUND TO OTHER
FUNCTIONS FOR USE LATER

19
req.id = ‘foo’;
console.log(req.id);

FOR EXAMPLE, SERVICE
BASED LOGGING

21
ASSIGN A REQUEST ID HERE
AND HAVE IT SENT ON TO ALL
OTHER SERVICES
WHICH MEANS ALLYOUR LOGS FROM ALLYOUR SERVICES ALLTIE TOGETHER

CLS
NODE-CONTINUATION-LOCAL-STORAGE
USERLAND MODULE
UTILISES ASYNC-LISTENER
24
/othiym23/node-continuation-local-storage
/ continuation-local-storage
/package/async-listener

IT HAS NOTHING TO DO WITH
LOCAL-STORAGE IN THE BROWSER

“Continuation-local storage
works like thread-local storage in
threaded programming, but is
based on chains of Node-style
callbacks instead of threads.”
26

IT MEANS YOU CAN STOP DOING THIS…
27
console.log('Got request with ID', res.id);
}
res.id = uuid();
respond(res);
});
});

AND START DOING THIS…
28
var createNamespace = require('continuation-local-storage').createNamespace;
var namespace = createNamespace('request-life');
console.log('Got request with ID', namespace.get('requestId'));
}
namespace.set('requestId', uuid());
respond(res);
});
console.log('Server listening on: http://localhost:8080');
});

IT’S MORE IMPRESSIVE THAN IT
LOOKS IN THIS SIMPLE EXAMPLE
I PROMISE

THAT’S AWESOME!
WHAT DO I NEED TO DO?

1
31
var createNamespace = require('continuation-local-storage').createNamespace;
var session = createNamespace('my session');
var db = require('./lib/db.js');
function start(options, next) {
db.fetchUserById(options.id, function (error, user) {
if (error) return next(error);
session.set('user', user);
next();
});
}

2
32
var getNamespace = require('continuation-local-storage').getNamespace;
var session = getNamespace('my session');
var render = require('./lib/render.js')
function finish(response) {
var user = session.get('user');
render({user: user}).pipe(response);
}

SO IT JUST WORKS?
I DON’T HAVE TO DO ANYTHING FUNKY?

ANYTHING THAT TOUCHES NATIVE
CODE; YOU’LL NEED TO SHIM

/package/shimmer
/othiym23/shimmer

39
var shimmer = require('shimmer');
shimmer.wrap(http, 'request', function (original) {
return function () {
console.log("Starting request!");
var returned = original.apply(this, arguments)
console.log("Done setting up request -- OH YEAH!");
return returned;
};
});

41
require('cls-mysql')(ns);
require('cls-redis')(ns);
require('cls-q')(ns);
require('cls-bluebird')(ns);
require('cls-es6-promise')(ns);
require('cls-bcrypt')(ns);

44
// Copyright (c) 2015. David M. Lee, II
'use strict';
var shimmer = require('shimmer');
// require mysql first; otherwise you can get some bizarre
// "object is not a function" errors if cls-mysql is loaded first.
require('mysql');
var Protocol = require('mysql/lib/protocol/Protocol');
var Pool = require('mysql/lib/Pool');
module.exports = function(ns) {
shimmer.wrap(Protocol.prototype, '_enqueue', function(enqueue) {
return function(sequence) {
sequence._callback = ns.bind(sequence._callback);
return enqueue.call(this, sequence);
};
});
shimmer.wrap(Pool.prototype, 'getConnection', function(getConnection) {
return function(cb) {
return getConnection.call(this, ns.bind(cb));
};
});
};

YOU HAVE TO KNOW WHAT
TO SHIM!

AND BEWARE THE INTERNALS
OF THE MODULE CHANGING

AN INTERNAL
MODULE CHANGE !== A PUBLIC API
CHANGE

WHICH MEANS YOU COULD BE
HIT BY A MINOR VERSION BUMP

WHICH COULD RESULT IN A
FAILING APPLICATION

IT ALSO HAS A PERFORMANCE COST
THE MORE YOU HAVE,THE MORE YOU’LL IMPACTYOUR PERFORMANCE
COST IS AGAINST A NAMESPACE, NOT DATA IN THE NAMESPACE
KEEP THINGS TO A MINIMUM
50

IF YOU’RE DOING IT RIGHT…
YOU SHOULD BE USING SHRINKWRAP ANYWAY
(OR ANOTHER TECHNIQUE TO LOCK DEPENDENCIES)
SO BREAKAGES SHOULD BE LIMITED TO YOUR DEVELOPMENT ENVIRONMENT
WHICH MEANS MOAR BONUS FOR LITTLE TO NO RISK
VERY LOW PERFORMANCE COST
52

THANKS!
DAN JENKINS
@dan_jenkins

MOST EXAMPLES WERE TAKEN FROM
https://github.com/othiym23/node-continuation-local-storage
https://github.com/othiym23/shimmer
https://github.com/building5/cls-mysql
54

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