event-driven – Page 3 – Türker Yıldırım

An event log that is not an event store

Deep diveAugust 10, 202310 min read

Wanting to know what happened to an order without adopting event sourcing. A support question that takes twenty minutes and three tables.

Message versioning by adding fields only

NoteJune 15, 20231 min read

A message shape is a contract with every consumer that exists and every consumer that is mid-deploy. Adding an optional field is safe because an old consumer ignores…

An outbox table, and the relay that reads it

NoteFebruary 20, 20231 min read

Publishing to a broker inside a database transaction is two systems and one commit, which cannot be made atomic. The index on (published_at, id) with nulls first is…

At-least-once, and the consumer that had to say so

NoteFebruary 14, 20232 min read

Every broker worth using delivers at least once, and every consumer that does not say how it handles that is claiming something it has not checked. Writing the…

The webhook we sent, and the retries we owed

Deep diveDecember 7, 202210 min read

Being the sender, for the first time, and the obligations that come with it. A customer endpoint that was down for six hours.

An event is past tense and cannot be refused

NoteNovember 23, 20221 min read

The naming convention decides who is allowed to fail, which is why it is worth more than a style rule. A handler for OrderPlaced that throws does not…

An idempotent consumer for a broker that redelivers

Deep diveNovember 8, 202210 min read

A message processed twice, and a customer charged twice. At-least-once delivery, treated as exactly-once by the handler.

Asserting an event was dispatched, not that a mail was sent

NoteMay 31, 20221 min read

Testing the effect couples the test to the listener, and testing the event tests the thing the code under test is actually responsible for. The listener gets its…

Sharded pub/sub, and the cluster that could not broadcast

Deep diveApril 25, 20229 min read

A broadcast that goes to every node on every publish. Classic pub/sub does not scale in a cluster, and 7.0 gives channels that respect slots.

An audit log that a lawyer could read

Deep diveFebruary 10, 20229 min read

A dispute, and a log that recorded that something changed. “Order updated” with no before, no after and no actor.