An overview of how Node.js cluster module works, what you can do with it and what you should take care of when using it.

1. Globalcode – Open4education
Node.js Cluster
Derek Stavis
Software Engineer

2. Globalcode – Open4education
Who?
Derek Stavis
github.com/derekstavis
Software Engineer
@ Pagar.me
Ruby, JavaScript, Python, Go, C
Node, React & Webpack Advocate

3. Globalcode – Open4education
Node.js Runtime

4. Globalcode – Open4education
single threaded
non-blocking
asynchronous
concurrent
engine

5. Globalcode – Open4education
Heap
Memory Available
Task Queue
listOnTimeout
listOnTimeout
listOnTimeout
listOnTimeout
listOnTimeout
Delayed Tasks
Call Stack
write()
saveFile()
updateTime()
tryOnTimeout
listOnTimeout
Execution Contexts
Vendor APIs (Node, Web)
Runtime and Platform Abstraction
Event Loop
Task Scheduler

6. Globalcode – Open4education
Single threaded

7. Globalcode – Open4education
Isn’t concurrent
sufficient?

8. Globalcode – Open4education
We have multiple
processors for a while

9. Globalcode – Open4education
We want to distribute
the load

10. Globalcode – Open4education
Enter cluster module

11. Globalcode – Open4education
const cluster = require('cluster');
const http = require('http');
const numCPUs = require('os').cpus().length
How to

12. Globalcode – Open4education
if (cluster.isMaster) {
console.log(`Master ${process.pid} is running`);
// Fork workers.
for (let i = 0; i < numCPUs; i++) {
cluster.fork();
}
cluster.on('exit', (worker, code, signal) => {
console.log(`worker ${worker.process.pid} died`);
});
}
How to

13. Globalcode – Open4education
else {
// Workers can share any TCP connection
// In this case it is an HTTP server
http.createServer((req, res) => {
res.writeHead(200);
res.end('hello worldn');
}).listen(8000);
console.log(`Worker ${process.pid} started`);
}
How to

14. Globalcode – Open4education

15. Globalcode – Open4education
What?

16. Globalcode – Open4education
Two processes binding
on the same port?

17. Globalcode – Open4education
cluster is just a wrapper
for child_process.fork

18. Globalcode – Open4education
Socket.listen is aware
of cluster module

19. Globalcode – Open4education
When a “slave” process
uses a Socket

20. Globalcode – Open4education
The underlying
implementation listens
on a file descriptor

21. Globalcode – Open4education
That is fed by the
master process

22. Globalcode – Open4education
Master process acts like a
load balancer

23. Globalcode – Open4education

24. Globalcode – Open4education
Perk: You can do
clustering with anything
that is socket based

25. Globalcode – Open4education
Here comes the Jabá

26. Globalcode – Open4education
TeleMMO is a
RPG game into a
Telegram bot

27. Globalcode – Open4education
We needed to make our
game multicore

28. Globalcode – Open4education
Telegram API can use
two modes: Polling and
Webhook

29. Globalcode – Open4education
Webhooks are based on a
HTTP server

30. Globalcode – Open4education
We use a third-party
module to integrate with
Telegram

31. Globalcode – Open4education
Cluster came in handy

32. Globalcode – Open4education
We just followed the
standard path
(click me)

33. Globalcode – Open4education

34. Globalcode – Open4education
What more?

35. Globalcode – Open4education
You can do nice things

36. Globalcode – Open4education
Zero downtime
code reload

37. Globalcode – Open4education
Process management

38. Globalcode – Open4education
Automatic software
update

39. Globalcode – Open4education
var recluster = require('recluster'),
path = require('path');
var cluster = recluster(path.join(__dirname, 'server.js'));
cluster.run();
process.on('SIGUSR2', function() {
console.log('Got SIGUSR2, reloading cluster...');
cluster.reload();
});
console.log("spawned cluster, kill -s SIGUSR2", process.pid, "to reload");
https://github.com/doxout/recluster

40. Globalcode – Open4education
Is it all flowers?

41. Globalcode – Open4education
NOPE

42. Globalcode – Open4education
Processes are heavy

43. Globalcode – Open4education
They are subject to
operating system
scheduling

44. Globalcode – Open4education
Context switches are
very expensive

45. Globalcode – Open4education
Memory usage is high

46. Globalcode – Open4education
Each worker reloads the
entire application into
memory

47. Globalcode – Open4education
Kinda hacky, huh?

48. Globalcode – Open4education
So, use it wisely

49. Globalcode – Open4education
Don’t do more
processes than the
number of CPUs

50. Globalcode – Open4education
Don’t use it to fix your
bad code performance

51. Globalcode – Open4education

52. Globalcode – Open4education
Thanks for watching
Questions?
github.com/derekstavis
twitter.com/derekstavis
facebook.com/derekstavis