QCon NewYork 2016: The Verification of a Distributed System

Distributed Systems are difficult to build and test for two main reasons: partial failure & asynchrony. These two realities of distributed systems must be addressed to create a correct system, and often times the resulting systems have a high degree of complexity. Because of this complexity, testing and verifying these systems is critically important. In this talk we will discuss strategies for proving a system is correct, like formal methods, and less strenuous methods of testing which can help increase our confidence that our systems are doing the right thing.

Transcript

1. The Verification of a Distributed System A Practitioner’s Guide to Increasing Confidence in System Correctness
2. Distributed Systems Engineer Caitie McCaffrey caitiem.com @caitie
4. LESLIE LAMPORT “A Distributed System is one in which the failure of a computer you didn’t even know existed can render your own computer unusable”
5. Service Service Service We Are All Building Distributed Systems
6. Twitter Services
8. Overview Formal Verification Provably Correct Systems Testing in the Wild Increase Confidence in System Correctness Research A New Hope
9. References
10. Provably Correct Formal Verification
11. Formal Specifications Written description of what a system is supposed to do TLA+ Coq
12. Hour Clock Specification ————————————— MODULE HourClock ———————————————— EXTENDS Naturals VARIABLE hr HCini == hr \in (1 .. 12) HCnxt == hr’ = IF hr # 12 THEN hr + 1 ELSE 1 HC == HCini /\ [][HCnxt] _hr ————————————————————————————————————————————- THEOREM HC => []HCini ============================================= Leslie Lamport, Specifying Systems TLA+
13. Use of Formal Methods at Amazon Web Services TLA+
14. “Formal Methods Have Been a Big Success” S3 & 10+ Core Pieces of Infrastructure Verified 2 Serious Bugs Found Increased Confidence to make Optimizations Use of Formal Methods at Amazon Web Services TLA+
15. “Formal methods deal with models of systems, not the systems themselves” Use of Formal Methods at Amazon Web Services
16. Leslie Lamport, Specifying Systems “Its a good idea to understand a system before building it, so its a good idea to write a specification of a system before implementing it” TLA+
17. Program Extraction
18. POPL 2016 “Our Verified Implementation is extracted to OCaml & runs on real networks” Program Extraction COQ
19. POPL 2016 “We have developed & checked our framework in Coq, extracted it to OCaml, and built executable stores” Program Extraction COQ
20. Distributed Systems Testing in the Wild “Seems Pretty Legit”
21. Unit Tests Testing of Individual Software Components or Modules
22. Simple Testing Can Prevent Most Critical Failures
23. 77% of Production failures can be reproduced by a Unit Test Simple Testing can Prevent Most Critical Failures
24. Error Handling Code is simply empty or only contains a Log statement Error Handler aborts cluster on an overly general exception Error Handler contains comments like FIXME or TODO 35% of Catastrophic Failures Simple Testing can Prevent Most Critical Failures
25. Scala Types Are Not Testing A Short Counter Example
26. TCP Doesn’t Care About Your Type System
27. Integration Tests Testing of integrated modules to verify combined functionality
28. Three nodes or less can reproduce 98% of failures Simple Testing can Prevent Most Critical Failures
29. Property Based Testing
30. QuickCheck ScalaCheck Haskell Erlang Scala Java & & C, C++, Clojure, Common Lisp, Elm, F#, C#, Go, JavaScript, Node.js, Objective-C, OCaml, Perl, Prolog, PHP, Python, R, Ruby, Rust, Scheme, Smalltalk, StandardML , Swift Languages with Quick Check Ports:
31. ScalaCheck Examples
32. Fault Injection Introducing faults into the system under test
33. -The Verification of a Distributed System “Without explicitly forcing a system to fail, it is unreasonable to have any confidence it will operate correctly in failure modes”
34. Netflix Simian Army • Chaos Monkey: kills instances • Latency Monkey: artificial latency induced • Chaos Gorilla: simulates outage of entire availability zone.
35. Kyle has used this tool to show us that many of the Distributed Systems we know seem stable but are really just this. (cut to tire fire photo) JEPSEN credit: @aphyr Fault Injection Tool that simulates network partitions in the system under test
36. Kyle has used this tool to show us that many of the Distributed Systems we know seem stable but are really just this. (cut to tire fire photo) JEPSEN credit: @aphyr Fault Injection Tool that simulates network partitions in the system under test
37. CAUTION: Passing Tests Does Not Ensure Correctness
38. GAME DAYS Resilience Engineering: Learning to Embrace Failure Breaking your services on purpose
39. How to Run a GameDay 1. Notify Engineering Teams that Failure is Coming 2. Induce Failures 3. Monitor Systems Under Test 4. Observing Only Team Monitors Recovery Processes & Systems, Files Bugs 5. Prioritize Bugs & Get Buy-In Across Teams Resilience Engineering: Learning to Embrace Failure
40. Game Day at Stripe “During a recent game day, we tested failing over a Redis cluster by running kill -9 on its primary node, and ended up losing all data in the cluster” Game Day Exercises at Stripe: Learning from `kill -9`
41. TESTING IN PRODUCTION Some thoughts on
42. Monitoring Testing is not
43. CANARIES “Verification” in production
44. Verification Wild in the Unit & Integration Tests Property Based Testing Fault Injection Canaries
45. Research Improving the Verification of Distributed Systems Lineage Driven Fault Injection ‘Cause I’m Strong Enough: Reasoning about Consistency Choices in Distributed Systems IronFleet: Proving Practical Distributed Systems Correct Towards Property Based Consistency Verification
46. ‘Cause I’m Strong Enough POPL 2016
47. ‘Cause I’m Strong Enough: Reasoning About Consistency Choices in Distributed Systems
48. Conclusion Use Formal Verification on Critical Components Unit Tests & Integration Tests find a multitude of Errors Increase Confidence via Property Testing & Fault Injection
49. Camille Fournier “Enjoy the ride, have fun, and test your freaking code”
50. Thank You Peter Alvaro Kyle Kingsbury Christopher Meiklejohn Alex Rasmussen Ines Sombra Nathan Taylor Alvaro Videla
51. Questions @caitie http://github.com/CaitieM20/ TheVerificationOfDistributedSystem Resources: