Easy · Government and education
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. Practise this easy system design problem for free with a Google or GitHub account.
The brief
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.
Think of a state benefits site.
Users, scale and requirements
- Who uses it
- 1.5 million applicants a year (approx.)
- Audience in plain numbers
- 400,000 users or devices
- Normal peak
- ≈ 300 requests per second
- Request mix
- Read: 54%; Write: 20%; Sign-in: 15%; Upload: 4%; Notification: 5%; Report: 2%
- Speed for 99 of 100 requests
- Read: ≈ 700 ms; Write: ≈ 700 ms; Sign-in: ≈ 1,000 ms; Upload: ≈ 5,000 ms; Report: ≈ 10,000 ms
- Successful requests
- 99.5%
- Data safety
- No acknowledged write may be lost.
- Monthly budget
- ≈ $8,500
- Data at rest
- ≈ 10 TB
- Where users are
- North America: 100%
- Home region
- North America
- Waiting deadlines
- Read: 900 seconds; Write: 3,600 seconds; Sign-in: 900 seconds; Upload: 3,600 seconds; Notification: 900 seconds; Report: 3,600 seconds
- Minimum retained history
- 2,555 days on authoritative stores
- Fresh reads
- People must see their own changes. At most 0.1% of reads may be stale in the model.
- Personal reads
- 80% of reads are private; a shared public copy cannot answer them.
- Required proofs
- Signed-in access; Tested backups; Audit trail; Managed encryption keys; 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.
- Public agencies often have small budgets; cost counts.
- A "write" is saving a draft or submitting an application.
- 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
Can an application be lost?
No. Someone may be applying for help to eat. A saved form must stay saved.
How fast must an email "we got your application" go out?
Within minutes. It can wait in a line when the site is busy.
When is it busy?
The closing days of a month can bring four times the usual traffic over several hours.
Who looks at the forms afterwards?
Caseworkers, through an admin tool that runs heavy reports.
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 · Compliance audit
An auditor checks your design: who did what, encryption keys, personal data, backups and consent.
12:00 · Deadline surge
Tax day, enrollment close or a sign-up deadline. Traffic climbs for hours until the cut-off.
Traffic reaches 4 times the scheduled load; rises over 21,600 seconds, holds for 3,600 seconds and eases over 900 seconds.
What a strong design has to handle
- Which work can wait a few minutes without anyone minding?
- Pointing the caseworker reports at a replica keeps the heavy queries away from people saving forms, at the price of a second database.
- Synchronous copies make saves a few milliseconds slower and mean a zone failure cannot lose an application.
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
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