Notification system

Accept notification requests from many internal services and deliver them through push, SMS and email providers. The design is a durable queue between fast producers and slow, flaky third parties, with retries, rate limits and user preferences in between.

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Duration 45:00

Requirements checklist

Internal services send a notification for a user and a template; the system picks channels (push, SMS, email) from the user's preferences.Respect opt-outs, quiet hours and per-user frequency caps.Track status (queued, sent, delivered, failed) and retry transient failures.Accepting a request takes under 50 ms and never depends on provider health.At-least-once delivery to the provider, with duplicates suppressed where the channel allows (collapse IDs, idempotency keys).Time-sensitive notifications (2FA codes) delivered within seconds; marketing can wait.

Clarifying questions

Which channels, and which providers?
Which notifications are time-critical?
Is delivery confirmation required, or is 'handed to the provider' enough?
Expected campaign sizes and how fast they must go out?

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requirements

Suggested time: about 6 minutes. Separates acceptance latency from delivery latency and defines duplicate handling per channel.

Notes for requirements