Sagas os Elixir
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The document describes the author's experience as an Elixir developer and introduces the Sagas pattern for managing distributed transactions. It explains the challenges of traditional transaction methods, highlights the Sage library as a solution for implementing the Sagas pattern in Elixir, and provides detailed features and capabilities of Sage for booking systems. Finally, it emphasizes the benefits of using Sage for synchronizing state across microservices and databases while maintaining elegant logic organization.
Sagas os Elixir
- 2. ABOUT ME ▸ Elixir dev for 2+ years ▸ Worked on NHS of Ukraine and few other large projects ▸ Maintain 20+ public Elixir repos used in production ▸ Contribute back as much as I can
- 3. WE ARE GOING TO TALK ABOUT ▸ Why do we need distributed transactions? ▸ Sagas pattern ▸ Sage Elixir library ▸ Structuring your domain contexts (bonus)
- 4. IMAGINE WE ARE BUILDING A SIMPLE BOOKING WEBSITE Invariants: - We should not charge card if request was not fulfilled - We should not hold booking if charge is failed
- 6. WITH COMPILES TO NESTED CASES
- 9. LET'S MAKE IT HARDER
- 10. OOPS, FAILED TO BOOK A FLIGHT
- 12. WHAT IS WRONG? ▸ Bad for latency - can't book concurrently ▸ The syntax to track step on which failure occurred is ugly ▸ To test it you need a complex failure injection for API client stubs ▸ Easy to miss some errors - monster else clause
- 14. CAN WE DO BETTER? ▸ Refactor ▸ 2PC ▸ Sagas
- 15. SAGAS PATTERN Failure management pattern that originates from 1987’s paper on long running transactions for databases. A long lived transaction is a Saga if it can be written as a sequence of transactions that can be interleaved with other transactions. The database management system guarantees that either all the transactions in a Saga are successfully completed or compensating transactions are run to amend a partial execution.
- 16. HOW DOES IT WORK? ▸ Transaction is split into a multiple atomic steps ▸ Each step consist from transaction and compensation ▸ When transaction fails compensation are run to semantically amend it's effects ▸ Compensation and transactions should be idempotent
- 17. BOOKING SITE WITH SAGAS
- 19. SAGE Sage is a dependency-free pure Elixir library inspired by Sagas pattern. Provides set of additional features on top of steps, transactions and compensations defined by the original paper.
- 20. It's like Ecto.Multi but across business logic and third-party APIs. — @jayjun from #elixir-lang Slack channel
- 21. BOOKING EXAMPLE WITH SAGE
- 23. RETRIES
- 25. CIRCUIT BREAKERS
- 27. AND MORE ▸ Final callback ▸ Tracing ▸ Works with Ecto
- 28. ERROR HANDLING ▸ Sage transaction abort ▸ Compensation failure ▸ Bugs in Sage
- 29. THINGS TO COME ▸ Saga execution log ▸ Plug-style module callbacks ▸ Compile-time type checking
- 30. AND IT MAKES YOUR DOMAIN CONTEXTS BETTER
- 32. RECAP Use Sage to: ▸ Synchronize state across microservices ▸ Synchronize state across databases ▸ To run distributed transactions Sage can help to elegantly organize logic in your domain contexts. Still young but well-documented and covered with tests.
- 33. THANK YOU! QUESTIONS? github.com/nebo15/sage GitHub: AndrewDryga Twitter: andrew_dryga Elixir-Lang Slack: AndrewDryga Email: andrew@dryga.com