Presentation and code about asynchronous web-development with Python, presented at Holtzbrinck Tech Day 2014

1. Asynchronous web development
with Python
Anton Caceres
Stefan Behnel

2. About Us
Anton Caceres, Stefan Behnel –
Software Developers at Skoobe GmbH
Skoobe:
• eBook subscription service
• 45 000+ books
• new titles weekly
• Android and iOS

3. Every day,
almost 2 years of reading

4. Outline
• Web servers - threading vs. async
• Asynchronous programming basics
• Code session with Python/Tornado

5. Frontend and Backend
Many page resources, Ajax, WebSockets, …
!
More and more backend requests per client -
Are web-servers ready for it?
Options to solve the problem:
• Scale hardware
• Run efficient software

6. Threaded web server
HTTPServer
T
T
T
T
...
...
Client-Requests
The naïve approach:
every request in a new thread

7. Threaded web server
# requests
#responses
The naïve approach:
every request in a new thread

8. Threaded web server with pool
The better approach:
every request in a free thread from pool
HTTPServer
T
T
T
...
Client-Requests
}n

9. Threaded web server with pool
# requests
#responses
The better approach:
every request in a free thread from pool

10. Threaded web server problem
Common bottleneck:
Threads spend most time waiting for I/O
T
T
T
T
...
I/O
I/O
I/O
I/O
Blocking!
Client-Requests
HTTPServer

11. Asynchronous Web-ServerClient
Requests
...
Processing
Processing
ProcessingProcessing
I/O
Loop
Processing
The non-blocking approach:
Process whenever you can

12. The non-blocking approach
# requests
#responses
Asynchronous Web-Server

13. Asynchronous Web Server
Should be efficient not only for server,
but also for developers
!
Nice if your language provides:
● Coroutines
● Continuations
!
Not nice if you need to code callback-spaghetti

14. Nooooo!…
before(function (done) {!
server.server(options, function (s, db, providers) {!
//clear db and add a test user - "testuser"!
db.user.remove({}, function () {!
db.notification.remove({}, function () {!
providers.provider1.insertBulk(item1, item2, item3],!
function (err, result) {!
providers.provider2.insert([item1, item2, item3]!
function (err, result) {!
providers.provider3.insert([item1, item2, item3]!
function (err, result) {!
providers.provider4.insert([item1, item2, item3],!
function (err, result) {!
s.listen();!
done();!
})!
});!
});!
});!
});!
});!
});!
});
Real code from mongojs repository

15. Tornado Web Framework
● Single-threaded
● Asynchronous
● Scalable
● Simple
● Free (Apache license 2.0)
!
Similar to Node.js, EventMachine, …
Originally created at FriendFeed
Developed by Facebook

16. Writing asynchronous
code
The practical part

17. Overview
Simple use-case:
• A web-service that makes 3 requests to
external APIs and returns an aggregated
response to the client.
!
In practical part we will:
• Create a blocking handler with Tornado
• Make this handler asynchronous
• Run some benchmarks to compare Tornado
with other asynchronous frameworks

18. Blocking handler, Tornado

19. Making code run async
• Turn handler method into coroutine
• Change HTTPClient to AsyncHTTPClient to
make it return Futures
• Yield Futures back to IOLoop

20. Async handler, Tornado

21. More Async frameworks
There is a plenty of options for other
programming languages:
!
• Event Machine for Ruby
• Finagle for Scala
• Node.js
!
Next, same code for Node and Finagle

22. Async handler, Node.js

23. Async handler, Finagle
(thanks to Gutefrage.net guys)

24. Some benchmarks
Which server will handle an increasing
amount of parallel requests better?
!
Lets make a simple benchmark:
Change amount parallel requests from 1 to 20
Measure an average time it takes for different
web servers
Plot results on the graph

25. Some benchmarks

26. Some benchmarks

27. Some benchmarks
• Node.js is fastest in beginning, but slowest in
the end
• Finagle is slowest in beginning, but fastest in
the end
• Tornado is somewhere in the middle
• You could help with more examples?
Contact me!

28. Thank you!
Questions?
!
!
Anton: anton@caceres.me, Stefan: stb@skoobe.de