One order. Four teams need to know.

Understand it one step at a time

The short runs these in order in about 32 seconds. Here they are written out — pick any step to jump the short straight to it.

1. 1

   Order placed. Now what?

   Three things must happen next: send the email, reserve the stock, create the shipping label.

   order #A-7741 · placed 12:04:11

2. 2

   Checkout is calling all three

   Sequential HTTP calls inside the request. The customer waits for work they never asked about.

   checkout-api · 1,940ms and counting

3. 3

   Add a fourth, redeploy checkout

   Loyalty points want the same event. Now you edit and ship the one service nobody wants to touch.

   checkout-api · +1 dependency · redeploy

4. 4

   Fix: Azure Event Grid

   Checkout publishes one event and returns. It does not know who is listening, and does not care.

   shop-events · OrderPlaced published

5. 5

   One event, many subscriptions

   The subscription is the fan-out unit. Event Grid pushes to each handler — nobody polls anything.

   3 subscriptions · push delivery

6. 6

   Filters decide who gets what

   Event type, subject prefix, or a field inside the payload. A subscriber never sees what it filtered out.

   shipping-sub · subject: /orders/IN/

7. 7

   It retries, then dead-letters

   A failing handler gets exponential backoff for up to 24 hours — and only its own subscription is affected.

   shipping-sub · retry 4 · backoff

8. 8

   New subscriber, zero changes

   Loyalty creates its own subscription. Nobody edited checkout, nobody redeployed, nobody was consulted.

   loyalty-sub · created · 0 upstream edits

9. 9

   Which one? Grid, Hubs, Bus

   Commands to be done, facts to react to, and streams to be read. Three jobs, three services.

   Service Bus · Event Grid · Event Hubs

10. 10

    Publish the fact. Let them subscribe.

    The publisher should never hold a list of who cares. That list is the coupling.

    Azure Event Grid · shop-events