Medium · Finance and payments
Insurance claims
After a hailstorm, thousands of drivers file claims online, each with a handful of photos. The storm offer ends at 5 pm, so everyone files at the last minute. Every claim must be saved safely, and every customer gets a confirmation email. Practise this medium system design problem for free with a Google or GitHub account.
The brief
After a hailstorm, thousands of drivers file claims online, each with a handful of photos. The storm offer ends at 5 pm, so everyone files at the last minute. Every claim must be saved safely, and every customer gets a confirmation email.
Think of filing a car insurance claim online.
Users, scale and requirements
- Who uses it
- 3 million policyholders
- Audience in plain numbers
- 3,000,000 users or devices
- Normal peak
- ≈ 400 requests per second
- Request mix
- Read: 53%; Sign-in: 15%; Write: 10%; Upload: 10%; Report: 10%; Notification: 2%
- Speed for 99 of 100 requests
- Read: ≈ 400 ms; Sign-in: ≈ 1,000 ms; Write: ≈ 400 ms; Upload: ≈ 4,000 ms; Report: ≈ 3,000 ms
- Successful requests
- 99.9%
- Data safety
- No acknowledged write may be lost.
- Monthly budget
- ≈ $14,000
- Data at rest
- ≈ 40 TB
- Where users are
- North America: 100%
- Home region
- North America
- Waiting deadlines
- Read: 900 seconds; Sign-in: 900 seconds; Write: 3,600 seconds; Upload: 3,600 seconds; Report: 3,600 seconds; Notification: 120 seconds
- Minimum retained history
- 2,555 days on authoritative stores
- Personal reads
- 90% of reads are private; a shared public copy cannot answer them.
- Required proofs
- Audit trail; Managed encryption keys; Personal data isolated; Retention rules
≈ marks an approximation, just as in the game. Waiting deadlines measure the age of queued work and are separate from interactive response time.
- The storm-offer deadline is 5 pm, so load climbs for hours.
- Adjusters browse claims in an internal console.
- Scored data retention: at least 2555 days on active authoritative stores. Copies used only for search or reports can be rebuilt. Local device history and rollup policies still require the separate protocol check.
- Notification speed measures provider acceptance. Device receipt is outside this traffic model; check expiry, provider outcome and retries in the correctness trace before claiming delivery guarantees.
Questions that shape the design
Does the customer need an answer at once?
No. "We received your claim" is enough, and the confirmation email can follow within a minute or two.
How big are the photos?
About 3 MB each. They are evidence, so none may be lost.
How reliable is the email provider?
It takes about 1,000 emails a second but can fail for a while. A missed email is bad, a lost claim is worse.
What is kept for the regulator?
Personal data in one controlled place, encrypted, with an audit trail, and records kept for years.
The traffic day
Traffic concentrated in working hours. The clock covers 00:00 to 24:00 in the home region. Events add pressure on top of that normal traffic.
10:00 · Deadline surge
Tax day, enrollment close or a sign-up deadline. Traffic climbs for hours until the cut-off.
Traffic reaches 6 times the scheduled load; rises over 21,600 seconds, holds for 3,600 seconds and eases over 600 seconds.
14:00 · Dependency outage
An outside service fails calls during an outage.
Failed calls: 100%. Duration: ≈ 1,200 seconds.
17:30 · Compliance audit
An auditor checks your design: who did what, encryption keys, personal data, backups and consent.
What a strong design has to handle
- A claim should never be lost because a helper (email, a database) is slow. Where can a claim wait safely for a moment?
- Accept a durable claim before the cutoff and publish its confirmation reliably.
- Saving first and processing after means a claim can be accepted before a later check finds a problem. Support follows up, which is the normal process anyway.
- The queue adds seconds between "received" and "saved". In return the database and the email provider never see the surge at full speed.
Make a prediction, run a full traffic day, then compare the result. The in-game editorial opens after a finished day and includes measured reference designs.
Concepts to practise
Related problems
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Benefits application portal
People apply for food, health or housing help on a state site. Forms are long, people save drafts and upload documents, and a caseworker team reviews each one. The last week of the month is busy, and an auditor checks the privacy and access controls once a year.
- Hard
Tax filing deadline
A national tax site lets 30 million people file online. Most wait until deadline day, and traffic climbs all evening to a final-hour rush. People upload forms, check what they owe and pay. A mistake in a payment or a leak of tax data is a national story.
- Medium
Smart power grid
A power company has 5 million smart meters. Each reports usage every 15 minutes, and they all try on the quarter hour. Customers see their usage, billing needs exact totals for seven years, and a regulator checks that records are kept safely. Control commands to home batteries and thermostats must never run twice.
- Easy
Invoicing and billing
Small businesses create invoices, email them to customers and take card payments online. On the last working day of the month everyone sends and chases invoices at once. Nobody may get the same invoice email twice, and no invoice may vanish.