Amazon SNS

A managed pub-sub notification service. Publish to a topic, every subscriber to that topic gets the message. In this series it's used specifically for its SMS notification type, sending OTPs and failure notifications to a phone number rather than fanning out to multiple subscribers.

vs EventBridge

Both are pub-sub. SNS routes by topic; EventBridge routes by content, inspecting the whole event to decide a target. Reach for SNS when the job is simple fan-out or, as here, direct SMS/push delivery. Reach for EventBridge when routing needs to depend on what's inside the event.

Where this showed up

• Why I made QR code delivery asynchronous: SMS as the async notification mechanism.
• The frontend that never touches a password: sending the OTP itself.
• Three tries, then a different path: the failure-notification SMS.

Further Reading and Watching

• Docs: Sending SMS messages with Amazon SNS (AWS docs)