SNS — Simple Notification Service

Opening Scenario

A payment is confirmed. Three things need to happen: the order service updates the order status, the notification service sends an email to the customer, and the analytics service records the revenue event. All three are independent — they don't depend on each other's results. If you call each service synchronously from the payment service, you couple payment processing to three different services. If any one is slow or down, the payment call fails or slows. How do you trigger all three without depending on any of them?

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Question Progression

Concept 1: What is a pub/sub system and how does SNS implement it?

Question You need one event to trigger multiple independent consumers. What's the model that makes this possible without the producer knowing about each consumer?

Reasoning Direct calls from the producer to each consumer create tight coupling. If you add a fourth consumer, you have to…