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Design an on-call alerting system like PagerDuty

PremiumCloud infrastructureMedium

  • On call schedules
  • Escalation policies
  • Acknowledgement timeouts

Quick answer

This cloud infrastructure interview question asks you to design an on-call alerting system like PagerDuty. Aim for a design that runs reliably and securely in the cloud at a sensible cost, then explain the services, regions, deployment and trade-offs. Interviewers want to see how you balance reliability, security and cost.

The problem

Design an on-call alerting system like PagerDuty: monitoring tools send alert events, and the system finds who is on call, pages them by push, SMS and phone call, and escalates until someone acknowledges. The hard parts are paging reliably during big outages, schedule math across time zones and never losing or double-firing an escalation.

What must an on-call alerting system like PagerDuty do?

  • Event intake: Accept trigger, acknowledge and resolve events; a trigger with the same dedup key as an open incident joins it instead of paging again.
  • Schedules: Rotations with layers, handoff times in the team's time zone, and one-off overrides.
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How well must it do it?

  • Fast first page: The first notification leaves within 60 s of the trigger event at p99.
  • Never lose a page: An accepted event is never lost; paging survives losing a whole region or one delivery vendor.
3 more requirementsUnlock to see all

What scale should you design for?

Use these numbers in your estimates.

The scale numbers unlock with this questionUnlock

Key concepts

  • On call schedules
  • Escalation policies
  • Acknowledgement timeouts
  • Alert deduplication
  • Durable timers
  • SMS and voice failover

How you’ll practise

6 short steps · save and come back any time
  1. Requirements
  2. Environments and topology
  3. Deployment pipeline
  4. Reliability and disaster recovery
  5. Observability and cost
  6. Wrap-up

Lala, personalized to you, gives a hint when you ask and reviews your design when you are ready.

What do interviewers look for?

In any cloud infrastructure design round.

  • Clarifies availability, security and cost targets
  • Chooses managed services with reasons
  • Plans regions, zones and failover
  • Covers identity, secrets and network boundaries
  • Explains deployment, rollback and observability
  • Keeps an eye on cost as usage grows

Questions people ask about this interview question

Which design type is this question?
It is a cloud infrastructure question. You design an on-call alerting system like PagerDuty and explain your choices the way you would in an interview.
Is this question asked at entry level?
It is marked Medium. Entry-level engineers can practise it, but it expects you to reason about requirements and trade-offs, not only list components.
What should I cover first?
Start with the workloads, the availability target and the security and cost limits. Agree on scope with the interviewer before you design anything.
Can I practise it for free?
It is a premium question. Sign up and unlock it once for 10 credits; it then stays unlocked. When you finish, Lala, your personalized AI mentor, can review your design for 30 credits.

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Updated · Written by the SevyDevy team

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