Design a real-time analytics dashboard
PremiumReal-timeMedium
- SSE
- Widget subscriptions
- Shared feeds
Quick answer
This real-time interview question asks you to design a real-time analytics dashboard. Aim for a design that delivers updates to many users with low delay, then explain connections, fan-out, ordering and trade-offs. Interviewers want to see how you keep latency low, handle reconnects and stay correct under load.
The problem
Design the live delivery layer of a real-time analytics dashboard for a large online shop, like a live Grafana or Datadog dashboard. Per-second aggregates already exist; the job is to get them onto every open dashboard within seconds, keep them correct when late data changes them, and stay cheap when thousands watch the same screen.
Operations, marketing and on-call engineers keep dashboards open on big screens and laptops. Each dashboard has widgets such as orders per minute, revenue in the last hour, active users right now and checkout error rate, each with filters for country and platform. An aggregation service already reads every event and emits the per-second aggregates.
What must a real-time analytics dashboard do?
- Widgets: Counters, sums, rates, distinct users and top-10 lists over the last 1 minute, 5 minutes, 1 hour and today, each with a per-second sparkline for the last 5 minutes.
- Filters: Each widget can be filtered by country (200 values) and platform (web, android, ios, app-clip).
How well must it do it?
- Freshness: A widget reflects events up to 3 seconds old at p99.
- Cost: Adding a viewer to a popular dashboard must cost almost nothing; widget values are computed once per distinct view, not once per viewer.
What scale should you design for?
Use these numbers in your estimates.
The scale numbers unlock with this questionUnlock
Key concepts
- SSE
- Widget subscriptions
- Shared feeds
- Conflation
- Backfill on reconnect
- Late corrections
How you’ll practise
- Requirements
- Estimate
- Connections
- Message flow
- Delivery guarantees
- 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 real-time design round.
- Clarifies latency, ordering and delivery guarantees
- Chooses a connection model with reasons
- Explains fan-out to many receivers
- Handles reconnects, missed messages and duplicates
- Plans for hot spots and sudden traffic spikes
- States trade-offs between consistency and speed
Questions people ask about this interview question
- Which design type is this question?
- It is a real-time question. You design a real-time analytics dashboard 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 who sends and receives updates, how fast they must arrive and what order matters. 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