Design an HR Operations Notification Workflow

Problem Design a workflow for HR operations that notifies employees by SMS or email on events like a declared public holiday, a published notice, or salary-slip distribution. The prompt is deliberately open-ended — first clarify whether a full system design or an operational workflow is expected, and scope accordingly.

Functional requirements

• HR ops triggers an event (holiday, notice, payslip) with a target audience (all employees, a location, a department).
• The system resolves the audience to employee records (fetching contact details and channel preferences), renders a templated message, and delivers via SMS/email.
• Delivery reporting: who was notified, failures, resends.

Non-functional requirements

• Bursty fan-out: a company-wide notice may mean 10^5+ messages at once; individual sends may fail and need retries.
• Payslip notifications carry sensitive data → access control, no PII in logs, links to a secure portal rather than attachments.

Key components

• Event/trigger API or console for HR ops → audience resolution service (queries the employee directory), template service (per event type and locale), dispatch queue with channel adapters (email/SMS providers) — strategy pattern for pluggable channels, retry + DLQ, delivery-status store and report view.

Deep dives / trade-offs

• Queue-based fan-out vs synchronous send: burst absorption, provider rate limits, per-channel throttling.
• Idempotency (event id + employee id dedupe key) so retried batches don't double-send.
• Preference and compliance handling: opt-outs, quiet hours, mandatory vs optional notifications.