This document discusses the path to microservices and focuses on areas like interfaces, transparency, simplicity and performance. It describes how applications have evolved from simple system threads/processes models to more complex asynchronous models using event loops. It also discusses different technologies for building chat servers like actor models, channels in Clojure, and how Clojure is well suited for microservices with features like STM, channels and transducers that enable transparency, simplicity and performance.

1. Path to microservices
(in parentheses)
Vasiliy Avdiushkin
software engineer
Zalando Hamburg
Hamburg Clojure User Group
Zalando Tech Events Hamburg

2. Applications
“An application program
(app or application for short)
is a computer program
designed to perform a group
of coordinated functions, tasks,
or activities for the benefit
of the user.”
from Wikipedia

3. Why do applications look like that
today?

4. Path to microservices

5. Please, not today

6. Today

7. Today
Interconnected world

8. Areas of focus
• Interfaces
• Transparency
• Simplicity
• Performance

9. Areas of focus
• Interfaces
• Transparency
• Simplicity
• Performance

10. System threads/processes

11. System threads/processes

12. System threads/processes

13. System threads/processes
?!

14. System threads/processes
?!
CGI
Fast CGI
WSGI
Some
other GI

15. System threads/processes
Simple model
Isolation
Handled by OS
Limited amount of connections
Complex synchronisation
Performance
Resources

16. Event loop (epoll, kqueue, etc...)

17. Performance
Synchronisation
10K connections
Complex (async) model
No blocking allowed
No isolation
(need to handle global state)
Single threaded
Event loop (epoll, kqueue, etc...)

18. Dispatching complex IO logic

19. Epoll network coding in plain C

20. NIO in Java

21. Telnet chat in Javascript

22. Telnet chat in Erlang

23. Actor model

24. Actor model

25. Actor model

26. Actor model

27. Telnet chat in Clojure (+ aleph)

28. Chat server

29. User input channels...

30. ...and message buffer...

31. ...are connected this way

32. Delivering messages

33. Delivering messages

34. Transducers on channels

35. Release and deploy

36. Telnet chat in Clojure (+ aleph)

37. Transparency, simplicity,
performance

38. Channels
• Interactive
• Safe
• Buffered
• Immutable
• Not hiding anything

39. Clojure
• STM (atoms, references,
agents)
• Channels (core.async)
• Functional transformations
(transducers)
• Java interop
• Interactive development (REPL)
• As simple as possible
• But not simpler

40. “Not only is there no God,
but try finding a plumber on Sunday.”
Woody Allen

41. (filter #(contains? % :question))
Questions?