The document provides an overview of Ratpack, a high-performance Java web framework designed for asynchronous and non-blocking I/O. It discusses the reasons for choosing Ratpack over Dropwizard, highlights potential mistakes developers can make, and outlines current issues the team is facing with the framework. The retrospective notes that while the integration was more challenging and time-consuming than expected, confidence in the framework's benefits is gradually improving.

1. Ratpack
The story so far
Phill Barber - Team Thor - Team Cirrus - Energized Work

2. Agenda
● What is Ratpack?
● Why did we decide to use it?
● A look at the code.
● Mistakes you can make.
● Issues we currently face.
● Retrospective.

3. What is Ratpack?

4. What is ratpack?
● A high performance Java web framework.
● Asynchronous and non-blocking model.
● Aims to make asynchronous programming on the JVM easier.
● Built on Java 8 and Netty.
● Currently at version 1.1.1

5. What is ratpack? (continued)
Assuming your application is I/O bound, it offers the following
benefits:
● High throughput
● Low CPU usage
● Lower Memory usage (due to less threads)
All of these benefits are due to its threading model and using
non blocking I/O

6. Synchronous - Blocking I/O

7. Asynchronous - Non Blocking I/O

8. What is ratpack? (continued)
This efficiency comes with the cost of increased complexity.
● Steep learning curve.
● Easy to get wrong.
● Hard to debug.

9. Ratpack misconceptions
● Asynchronicity is internal only!
○ It’s just a web server.
○ It takes time to respond to http requests.
● Doesn’t improve latency.
○ If a downstream call takes 500ms, ratpack will take > 500ms to respond.
● If you are using Ratpack - it doesn’t mean your system will
necessarily perform any better.
○ You can make it perform worse!

10. Why did we decide to use
it?

11. Ratpack vs Dropwizard

12. Ratpack vs Dropwizard

13. Ratpack vs Dropwizard - Load profiles
Three load profiles were given to each application as detailed
below:
1. 5 minute duration, 100 JMeter Threads
2. 5 minute duration, 200 JMeter Threads
3. 5 minute duration, 300 JMeter Threads

14. Ratpack vs Dropwizard

15. Ratpack vs Dropwizard

16. Ratpack vs Dropwizard

17. Ratpack vs Dropwizard

18. Why did we decide to use it?
● We will be I/O bound.
● We will be at high load.
● Ratpack vs Dropwizard Performance Test revealed
encouraging stats.
● We had a sense of optimism that we’d pick up the async
challenges.

19. A look at the code

20. A look at the code - Overview
● Runnable Jar.
● main() method starts the server.
○ Simple and easy to start for testing.
● URIs mapped to Handlers.
● Execution model deals with Promises.
● We decided to use Rx Java in “service” layer and use
Observables.

21. A look at the code
● Happy path example.

22. A look at the code
● Happy path example.
● High throughput example.

23. A look at the code
● Happy path example.
● High throughput example.
● Deterministic demonstration.

24. Mistakes you can make
...BIG BIG mistakes!

25. Mistakes - Two Types
1. Dangerous mistakes.
2. Annoying mistakes.

26. Dangerous mistakes
● Calling a blocking method.
○ So many ways to do this.
IMPACT: ?

27. Dangerous mistakes
● Making new Threads
IMPACT: Memory & CPU increase -> Ultimately low
throughput

28. Annoying mistakes
● Not understanding execution model.
○ Not using Promises when you should.

29. Annoying mistakes
● Messing up Threads
○ Using Cassandra thread to call Cassandra.
○ Happened to us whilst implementing ListenableFuture

30. Issues we currently face

31. Issues (continued)
● Ratpack http client does not use a connection pool.
● AppDynamics integration still ongoing.

32. Issues
Performance related issue: At load, 1 in 1000 requests would not get a response.
● Hard to debug
● Thread dumps revealed that (big surprise) nothing was blocking. Where do you
go from here?
Now Resolved
● Was actually an issue related to secretly running in Development mode. InteliJ
IDEA
○ Issue #909

33. Retrospective

34. Retro / Assorted notes...
● It was harder than we expected.
● It took longer than expected to get up to speed.
● Rx bought us flexibility but introduced an extra learning curve.
● Cost vs Reward analysis is difficult but would have been a benefit.
● Monitoring our CPU and Memory usage is key to realising the benefit.
● Confidence is improving day by day… BUT…
● Still not proven - We’re not live yet!

35. Thanks!
Questions?
More info: http://phillbarber.blogspot.co.uk/
Code: https://github.com/phillbarber/ratpack-demo