This is a presentation I originally gave at PloneConf in Barcelone. In it, we will cover the main differences between sync and async servers. After that we’ll go through a few example scenarios and benchmarks showing their strengths and weaknesses. Find out more at https://medium.com/@skyscannereng Discover our app https://www.skyscanner.net/mobile.html

1. Putting sync/async
servers to test
Jordi Soucheiron

2. Who am I?
Putting sync/async servers to test
• Software engineer @ Skyscanner
• Python lover
• Systems administration and backend systems
background
• @jordixou
http://bit.ly/jordisync

3. What are we going to talk about?
• Sync/async models
• Assumptions
• Benchmarking
• Conclusions
• Questions
Putting sync/async servers to test
http://bit.ly/jordisync

4. How do sync servers (usually) work
Putting sync/async servers to test
http://bit.ly/jordisync

5. How do async servers (usually) work
Putting sync/async servers to test
http://bit.ly/jordisync

6. The test environment
• 3 docker containers
• aiohttp
• Flask
• nginx
• wrk
• used to stress test and gather data
• 2 threads, 10-100 connections, 30 seconds
• docker stats to gather container performance data
• Tested in a macbook pro 13” 2.9GHz i5
• Docker configured to use 4 cores and 4GB of RAM
Putting sync/async servers to test
http://bit.ly/jordisync

7. Nginx container
• Using openresty
• Hello world with delays:
• 0ms
• 100ms
• 200ms
• 1s
Putting sync/async servers to test
http://bit.ly/jordisync

8. Flask container
• Dockerfile
• Python 3.6.3
• Using gunicorn, 100 worker threads
Putting sync/async servers to test
http://bit.ly/jordisync

9. Flask container
• 2 endpoints
• IO bottleneck
• CPU bottleneck
Putting sync/async servers to test
http://bit.ly/jordisync

10. aiohttp container
• Dockerfile
• Python 3.6.3
• Using gunicorn, 1 worker per CPU
Putting sync/async servers to test
http://bit.ly/jordisync

11. aiohttp container
• 2 endpoints
• IO bottleneck
Putting sync/async servers to test
http://bit.ly/jordisync

12. aiohttp container
• 2 endpoints
• CPU bottleneck
Putting sync/async servers to test
http://bit.ly/jordisync

13. Assumptions
• Async servers use less memory
• Latency is smaller in sync servers
• Sync code is simpler
• Async code is harder to reason about
• Async servers can handle more
requests/seq
Putting sync/async servers to test
http://bit.ly/jordisync

14. Benchmarks
Putting sync/async servers to test
http://bit.ly/jordisync

15. Benchmarks
• Disclaimer:
• This is not gonna be a fair fight
Putting sync/async servers to test
http://bit.ly/jordisync

16. Benchmarks
Putting sync/async servers to test
http://bit.ly/jordisync
0.00
200.00
400.00
600.00
800.00
1000.00
1200.00
hello world cpu_waster 100ms 200ms 1s
Response time (lower is better)
nginx aiohttp flask

17. Benchmarks
Putting sync/async servers to test
http://bit.ly/jordisync
0.00
500.00
1000.00
1500.00
2000.00
2500.00
3000.00
3500.00
4000.00
4500.00
hello world cpu_waster 100ms 200ms 1s
Requests per second (higher is better)
nginx aiohttp flask

18. Benchmarks
Putting sync/async servers to test
http://bit.ly/jordisync
0
5
10
15
20
25
30
35
hello world cpu_waster 100ms 200ms 1s
Memory per request per second (lower is better)
nginx aiohttp flask

19. Assumptions review
• Async servers use less memory
• Latency is smaller in sync servers
• Sync code is simpler
• Async code is harder to reason about
• Async servers can handle more
requests/seq
Putting sync/async servers to test
http://bit.ly/jordisync

20. Conclusions
• Async servers are great for*:
• Slow dependencies
• Many external dependencies
• Data aggregation from multiple sources
• Microservices
• Lots of I/O
• Async is bad for*:
• Static content
• CPU intensive work
Putting sync/async servers to test
*generally
http://bit.ly/jordisync

21. Conclusions
• Pros:
• Lower memory footprint*
• Higher throughput (req/s)*
• Cons:
• Latency for simple sync requests is higher*
• Chasing bottlenecks is harder
Putting sync/async servers to test
*generally
http://bit.ly/jordisync

22. Questions?
• All feedback is welcome
• Slides and links to the code available here:
• http://bit.ly/jordisync
• Ping me at @jordixou
Putting sync/async servers to test
http://bit.ly/jordisync

23. Thank you