3factor app - Reliable Eventing

We discuss the second factor of Hasura’s 3factor app, Reliable Eventing, as Allen says he still _surfs_ the Internet (but really, does he?), it’s never too late for pizza according to Joe, and Michael wants to un-hear things.

This episode’s full show notes can be found at https://www.codingblocks.net/episode116, just in case you’re using your podcast player to read this.

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The Second Factor – Reliable Eventing

• Don’t allow for mutable state. Get rid of in memory state manipulation in APIs.
• Persist everything in atomic events.
• The event system should have the following characteristics:
  • Atomic – the entire operation must succeed and be isolated from other operations.
  • Reliable – events should be delivered to subscribers at least once.

Comparing the 3factor app Eventing to Traditional Transactions

Traditional application	3factor application
Request is issued, data loaded from various storage areas, apply business logic, and finally commit the data to storage.	Request is issued and all events are stored individually.
Avoid using async features because it’s difficult to rollback when there are problems.	Due to the use of the event system, async operations are much easier to implement.
Have to implement custom recovery logic to rewind the business logic.	Recovery logic isn’t required since the events are atomic.

Benefits of an Immutable Event Log

• Primary benefit is simplicity when dealing with recovery. There’s no custom business logic because all the event data is available for replayabili