The Verification of a Distributed System

Transcript

1. The Verification of a
   Distributed System
   A Practitioner’s Guide to Increasing Confidence in System Correctness
   

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2. Distributed Systems Engineer
   Caitie McCaffrey
   caitiem.com
   @caitie
   

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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”
   

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5. Service Service
   Service
   We Are All
   Building
   Distributed
   Systems
   

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6. Twitter
   Services
   

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8. Overview
   Formal Verification
   Provably Correct Systems
   Testing in the Wild
   Increase Confidence in System Correctness
   Research
   A New Hope
   

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9. References
   

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10. Provably
    Correct
    Formal
    Verification
    

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11. Formal Specifications
    Written description of what a system is supposed to do
    TLA+ Coq
    

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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+
    

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13. Use of
    Formal
    Methods at
    Amazon
    Web Services
    TLA+
    

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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+
    

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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+
    

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16. “Formal methods deal with
    models of systems, not the
    systems themselves”
    Use of Formal Methods at Amazon Web Services
    

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17. Program Extraction
    

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18. POPL
    2016
    “Our Verified
    Implementation is
    extracted to OCaml
    & runs on real
    networks”
    Program Extraction
    COQ
    

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19. POPL
    2016
    “We have developed &
    checked our framework
    in Coq, extracted it to
    OCaml, and built
    executable stores”
    Program Extraction
    COQ
    

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20. Distributed
    Systems Testing
    in the Wild
    “Seems Pretty Legit”
    

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21. Unit Tests
    Testing of Individual Software
    Components or Modules
    

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22. Simple
    Testing Can
    Prevent
    Most Critical
    Failures
    

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23. 77% of Production failures
    can be reproduced by a
    Unit Test
    Simple Testing can Prevent Most Critical Failures
    

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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
    

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25. Testing error handling
    code could have
    prevented 58% of
    catastrophic failures
    Simple Testing can Prevent Most Critical Failures
    

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26. Scala
    Types
    Are Not
    Testing
    A Short Counter Example
    

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27. TCP Doesn’t Care About
    Your Type System
    

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

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29. Three nodes or
    less can reproduce
    98% of failures
    Simple Testing can Prevent Most Critical Failures
    

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30. Property Based
    Testing
    

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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:
    

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32. ScalaCheck Examples
    

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33. Fault Injection
    Introducing faults into the system under test
    

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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”
    

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35. Netflix Simian Army
    • Chaos Monkey: kills instances
    • Latency Monkey: artificial latency
    induced
    • Chaos Gorilla: simulates outage
    of entire availability zone.
    

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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
    

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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
    

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38. CAUTION: Passing Tests
    Does Not Ensure Correctness
    

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

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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
    

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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`
    

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42. TESTING IN
    PRODUCTION
    Some thoughts on
    

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43. Monitoring
    Testing
    is not
    

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44. CANARIES
    “Verification” in production
    

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45. Verification
    Wild
    in the
    Unit & Integration Tests
    Property Based Testing
    Fault Injection
    Canaries
    

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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
    

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47. ‘Cause I’m
    Strong Enough
    POPL
    2016
    

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48. ‘Cause I’m Strong Enough: Reasoning About Consistency Choices in Distributed Systems
    

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49. Conclusion
    Use Formal Verification on
    Critical Components
    Unit Tests & Integration Tests find a
    multitude of Errors
    Increase Confidence via Property
    Testing & Fault Injection
    

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50. Camille Fournier
    “Enjoy the ride, have fun, and
    test your freaking code”
    

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51. Thank You
    Peter Alvaro
    Kyle Kingsbury
    Christopher
    Meiklejohn
    Alex Rasmussen
    Ines Sombra
    Nathan Taylor
    Alvaro Videla
    

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52. Questions
    @caitie
    https://github.com/CaitieM20/
    Talks/tree/master/
    TheVerificationOfADistributedSystem
    Resources:
    

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