The Verification of a Distributed System

The Verification of a Distributed System

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Caitie McCaffrey

December 05, 2016
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  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

  3. None
  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

  7. None
  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. 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+
  16. “Formal methods deal with models of systems, not the systems

    themselves” Use of Formal Methods at Amazon Web Services
  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. Testing error handling code could have prevented 58% of catastrophic

    failures Simple Testing can Prevent Most Critical Failures
  25. 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
  26. Scala Types Are Not Testing A Short Counter Example

  27. TCP Doesn’t Care About Your Type System

  28. Integration Tests Testing of integrated modules to verify combined functionality

  29. Three nodes or less can reproduce 98% of failures Simple

    Testing can Prevent Most Critical Failures
  30. Property Based Testing

  31. 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:
  32. ScalaCheck Examples

  33. Fault Injection Introducing faults into the system under test

  34. -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”
  35. Netflix Simian Army • Chaos Monkey: kills instances • Latency

    Monkey: artificial latency induced • Chaos Gorilla: simulates outage of entire availability zone.
  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. 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
  38. CAUTION: Passing Tests Does Not Ensure Correctness

  39. GAME DAYS Resilience Engineering: Learning to Embrace Failure Breaking your

    services on purpose
  40. 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
  41. 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`
  42. TESTING IN PRODUCTION Some thoughts on

  43. Monitoring Testing is not

  44. CANARIES “Verification” in production

  45. Verification Wild in the Unit & Integration Tests Property Based

    Testing Fault Injection Canaries
  46. 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
  47. ‘Cause I’m Strong Enough POPL 2016

  48. Bank Application Bank Account must be > 0 Deposit Money

    Withdrawal Money
  49. ‘Cause I’m Strong Enough: Reasoning About Consistency Choices in Distributed

    Systems
  50. Conclusion Use Formal Verification on Critical Components Unit Tests &

    Integration Tests find a multitude of Errors Increase Confidence via Property Testing & Fault Injection
  51. Camille Fournier “Enjoy the ride, have fun, and test your

    freaking code”
  52. Thank You Peter Alvaro Kyle Kingsbury Christopher Meiklejohn Alex Rasmussen

    Ines Sombra Nathan Taylor Alvaro Videla
  53. Questions @caitie https://github.com/CaitieM20/ Talks/tree/master/ TheVerificationOfADistributedSystem Resources: