Lost in transaction - Strategies to deal with (in)consistency in distributed systems
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This document discusses strategies for dealing with inconsistency in distributed systems. It begins by introducing the concepts of atomicity, consistency, isolation, and durability (ACID) and how distributed systems violate the isolation aspect of ACID. It then discusses various strategies for handling failures and inconsistencies like two-phase commit, idempotent operations, retrying operations, and sagas with compensation. It argues that orchestration is preferable to choreography for long-running processes. Finally, it discusses workflow engines and platforms that can be used to implement orchestration.
Lost in transaction - Strategies to deal with (in)consistency in distributed systems
- 1. @berndruecker Lost in transaction? Strategies to deal with (in)consistency in distributed systems
- 2. Do A Do B All or nothing + try { tx.begin(); doA(); doB(); tx.commit(); } catch (Exception e) { tx.rollback(); } @Transactional public void createCustomer(Customer cust) { // ... } Or simply: Once upon a time:
- 7. But there is two-phase commit (XA)!! TX Coordinator Resource Managers Prepare Phase Commit Phase
- 8. Pat Helland “ Distributed Systems Guru Worked at Amazon, Microsoft & Salesforce
- 9. Pat Helland Grown-Ups Don’t Use Distributed Transactions “ Distributed Systems Guru Worked at Amazon, Microsoft & Salesforce
- 10. Starbucks does not use two phase commit https://www.enterpriseintegrationpatterns.com/ramblings/18_starbucks.html Photo by John Ingle
- 12. That means Do A Do B Temporarily inconsistent Eventually consistent again t Consistent Local ACID Local ACID 1 (micro-)service 1 aggregate 1 program 1 resource Violates „I“ of ACID
- 13. Youmightknowthisfrom: Do A Do B Temporarily inconsistent Eventually consistent again t Consistent Photo by Gerhard51, available under Creative Commons CC0 1.0 license.
- 14. „Building on Quicksand“ Paper A C I D 2.0Pat Helland
- 15. Associative Commutative Idempotent Distributed 2.0 (a + b) + c = a + (b + c) a + b = b + a f(x) = f( f(x) ) „Building on Quicksand“ Paper Pat Helland
- 16. Requirement: Idempotency of services! Photo by pixabay, available under Creative Commons CC0 1.0 license.
- 17. Requirement: Idempotency of services! Photo by Chr.Späth, available under Public Domain.
- 18. Associative Commutative Idempotent Distributed 2.0 (a + b) + c = a + (b + c) a + b = b + a f(x) = f( f(x) ) „Building on Quicksand“ Paper Pat Helland
- 19. Distributed
- 20. It is impossible to differentiate certain failure scenarios: Independant of communication style! Service Provider Client
- 22. Strategy: retry Credit Card Payment Charge Credit Card cardNumber amount Charge Credit Card cardNumber amount transactionId Not idempotent Idempotent has to be idempotent charge
- 23. Strategy: Cleanup Credit Card Payment charge Make sure it is not charged! Cancel charge cardNumber amount transactionId Raise payment failed
- 24. Some communication challenges require state.
- 26. Strategy: Stateful retry Credit Card Payment charge Make sure it is not charged!
- 28. Berlin, Germany bernd.ruecker@camunda.com @berndruecker Bernd Ruecker Co-founder and Developer Advocate of Camunda
- 29. Let‘s use a lightweight OSS workflow engine for this:
- 31. Stateful retry & cleanup Credit Card Payment REST
- 33. Embedded Engine Example (Java) https://blog.bernd-ruecker.com/architecture-options-to-run-a-workflow-engine-6c2419902d91
- 34. Remote Engine Example (Polyglot) https://blog.bernd-ruecker.com/architecture-options-to-run-a-workflow-engine-6c2419902d91
- 35. A relatively common pattern Service (e.g. Go) Kafka / Rabbit RDMS 1. Receive 4. Send additional events 2. Business Logic 3. Send response? ACK
- 39. That means Do A Do B Temporarily inconsistent Eventually consistent In case of failure: Compensate or apologise t Consistent
- 42. Compensation – the classical example Saga book hotel book car book flight cancel hotel cancel car 1. 2. 3. 5.6. In case of failure trigger compensations book trip
- 43. 2 alterntive approaches: choreography & orchestration
- 45. Event-driven choreography Hotel Flight Car Trip Trip failed Trip requested Hotel booked Car booked Request trip Flight failed Car canceled Hotel canceled Perform undo (cancel car booking) Perform undo (cancel hotel)
- 46. The danger is that it's very easy to make nicely decoupled systems with event notification, without realizing that you're losing sight of that larger-scale flow, and thus set yourself up for trouble in future years. https://martinfowler.com/articles/201701-event-driven.html
- 47. The danger is that it's very easy to make nicely decoupled systems with event notification, without realizing that you're losing sight of that larger-scale flow, and thus set yourself up for trouble in future years. https://martinfowler.com/articles/201701-event-driven.html
- 48. The danger is that it's very easy to make nicely decoupled systems with event notification, without realizing that you're losing sight of that larger-scale flow, and thus set yourself up for trouble in future years. https://martinfowler.com/articles/201701-event-driven.html
- 49. Classical example Saga book hotel book car book flight cancel hotel cancel car 1. 2. 3. 5.6. In case of failure trigger compensations book trip
- 50. If your transaction involves 2 to 4 steps, choreography might be a very good fit. However, this approach can rapidly become confusing if you keep adding extra steps in your transaction as it is difficult to track which services listen to which events. Moreover, it also might add a cyclic dependency between services as they have to subscribe to one another’s events. Denis Rosa Couchbase https://blog.couchbase.com/saga-pattern-implement-business-transactions-using-microservices-part/
- 51. Microservice pioneers have become aware
- 52. Implementing changes in the process Hotel Flight Car Trip Trip failed Trip requested Hotel booked Car booked Request trip Flight failed Car canceled Hotel canceled We have a new basic agreement with the car rental agency and can cancel for free within 1 hour – do that first!
- 53. Implementing changes in the process Hotel Flight Car Trip Trip failed Trip requested Hotel booked Car booked Request trip Flight failed Car canceled Hotel canceled You have to adjust all services and redeploy at the same time! We have a new basic agreement with the car rental agency and can cancel for free within 1 hour – do that first!
- 54. Photo by born1945, available under Creative Commons BY 2.0 license.
- 55. What we wanted Photo by Lijian Zhang, available under Creative Commons SA 2.0 License and Pedobear19 / CC BY-SA 4.0
- 57. Orchestration Hotel Flight Car Trip Trip booked Request trip Book hotel Hotel booked Car booked Flight booked Book car Book flight We have a new basic agreement with the car rental agency and can cancel for free within 1 hour – do that first! You have to adjust one service and redeploy only this one!
- 58. Describe orchestration with BPMN Trip Trip booked Request trip
- 59. The workflow is part of the service Trip
- 60. The workflow is part of the service Trip Payment
- 61. The workflow is part of the service Trip Payment Workflow engine itself can run decentralized or centralized
- 62. Caitie McCaffrey | @caitie
- 63. Saga Execution Coordinator (SEC) Hotel Flight Car Trip Trip booked Request trip SEC
- 64. Saga Execution Coordinator (SEC) Hotel Flight Car Trip SEC Requirement: Resilient and scalable Owned by executed by
- 65. Saga Execution Coordinator (SEC) Hotel Flight Car Trip SEC Requirement: SEC is resilient and scalable
- 66. „Can this really handle 15k requests per second?“
- 70. Clemens Vasters Architect at Microsoft http://vasters.com/archive/Sagas.html
- 71. Clemens Vasters Architect at Microsoft http://vasters.com/archive/Sagas.html
- 72. Clemens Vasters Architect at Microsoft http://vasters.com/archive/Sagas.html
- 73. BPMN Business Process Model and Notation ISO Standard
- 74. Living documentation for long-running behaviour
- 75. Visual HTML reports for test cases
- 76. BizDevOps
- 77. Saga with AWS Step Functions https://theburningmonk.com/2017/07/applying-the- saga-pattern-with-aws-lambda-and-step-functions/
- 78. Visibility gets easy when you know where to look
- 79. Thoughts on the state machine | workflow engine market
- 80. Thoughts on the state machine | workflow engine market OSS Workflow or Orchestration Engines Stack Vendors, Pure Play BPMS Low Code Platforms Homegrown frameworks to scratch an itch Integration Frameworks Cloud Offerings Uber, Netflix, AirBnb, ING, … AWS Step Functions, Azure Durable Functions, … Camunda, Zeebe, jBPM, Activiti, Mistral, … PEGA, IBM, SAG, … Apache Airflow, Spring Data Flow, … Apache Camel, Balerina, … Data Pipelines
- 81. Does it support stateful operations? Does it support the necessary flow logic? Does it support BizDevOps? Does it scale?
- 82. My personal pro-tip for a shortlist ;-) OSS Workflow or Orchestration Engines Stack Vendors, Pure Play BPMS Low Code Platforms Homegrown frameworks to scratch an itch Integration Frameworks Cloud Offerings Data Pipelines Camunda & Zeebe
- 83. Recap • Grown ups don‘t use distributed transactions but eventual consistency • Idempotency is super important in distributed systems • Some consistency challenges require state • Know some strategies • Stateful retry & cleanup • Saga / Compensation • Apologies
- 84. Thank you!
- 85. bernd.ruecker@camunda.com @berndruecker https://bernd-ruecker.com https://blog.bernd-ruecker.com https://github.com/flowing https://www.infoq.com/articles/events- workflow-automation With thoughts from http://flowing.io @berndruecker | @martinschimak Contact: Slides: Blog: Code: https://www.infoworld.com/article/3254777/ application-development/ 3-common-pitfalls-of-microservices- integrationand-how-to-avoid-them.html https://thenewstack.io/5-workflow-automation- use-cases-you-might-not-have-considered/