sagas.pdf

Sagas pattern and how to use it to run distributed transactions across domain contexts, microservices, databases and third-party API's with Elixir.

Transcript

1. SAGAS OF ELIXIR
2. ABOUT ME ▸ 14 years in IT, 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
7. HANDLING FAILURES
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. DISTRIBUTED TRANSACTIONS ARE EVERYWHERE ▸ CRM and Campaign Automation (Salesforce, Hubspot, Intercom, Autopilot) ▸ Payment Processors (Stripe, Braintree, PayPal) ▸ Analytics (GA, Mixpanel) ▸ Cloud Providers (Google Cloud, AWS) ▸ Any other SaaS integration ▸ Microservices
15. CAN WE DO BETTER? ▸ Refactor ▸ 2PC ▸ Sagas
16. 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.
17. 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
18. BOOKING SITE WITH SAGAS
19. AWESOME! ANYTHING FOR ELIXIR?
20. 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.
21. It's like Ecto.Multi but across business logic and third-party APIs. — @jayjun from #elixir-lang Slack channel
22. BOOKING EXAMPLE WITH SAGE
23. ASYNCHRONOUS TRANSACTIONS
24. RETRIES
26. CIRCUIT BREAKERS
28. AND MORE ▸ Final callback ▸ Tracing ▸ Easier to test ▸ Works with Ecto
29. ERROR HANDLING ▸ Sage transaction abort ▸ Compensation failure ▸ Bugs in Sage
30. THINGS TO COME ▸ Saga execution log ▸ Compile-time type checking
31. AND IT MAKES YOUR DOMAIN CONTEXTS BETTER
33. 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.
34. THANK YOU! QUESTIONS? github.com/nebo15/sage GitHub: AndrewDryga Twitter: andrew_dryga Elixir-Lang Slack: AndrewDryga Email: andrew@dryga.com