Scalability in Node.js is not an afterthought. It’s something that’s baked into the core of the runtime. Node is named Node to emphasize the idea that a Node application should comprise multiple small distributed nodes that communicate with each other.

1. Scaling node.js apps
@akts – 2018/03/16

2. What is scaling ?
app dbInternet
● Availability.
● Tolerance to failure.
● Share workload.

3. A simple solution
app 1 db
Internet
app 3
app 0
app 2
Load
balancer

4. node.js
● Single threaded - can only use one core of our CPU - ( Bad )
● Non-blocking – God bless the event loop ! – ( Good )
● Modules for scalability baked into the run-time - ( Awesome )

5. Things we can do
● Clonning:
● Clone app multiple times.
● Each cloned instance handles part of the load.
● Minimum strategy – low development time, highly effective.
● The infamous cluster module.
● Decomposing:
● Multiple, different applications with different code bases
● They might even score dedicated DBs and UIs
● Microservice – service should be as small as possible (Not really)
● Not easy, unexpected problems
● Splitting:
● Split into multiple instances, each instance for part of app data
● Horizontal partitioning / sharding
● Requires lookup logic

6. The cluster module
Master
w1 w2 w3 w4
Server
Round robin – Priorities - Least Loaded
· · ·
Useful for deploying to single machines

7. Let’s use it – Demo Time
● Have apache bench, siege or any other load test tool.
$ sudo apt install apache2-utils siege
● 200 concurrent users for 10 seconds
● Load-Balancing an HTTP Server
● Broadcasting Messages to All Workers
● Increasing Server Availability
● Zero-downtime Restarts
● An ode to PM2
$ sudo npm install -g pm2
$ pm2 start server.js -i max
$ pm2 reload all
● Shared State and Sticky Load Balancing

8. That’s all folks
● https://medium.freecodecamp.org/scaling-node-js-applications-8492bd8afadc - literally this presentation
● https://medium.freecodecamp.org/node-js-child-processes-everything-you-need-to-know-e69498fe970a
● https://www.youtube.com/watch?v=w1IzRF6AkuI
References a.k.a People I ripped off for this presentation
☮ ♡