39. Design a Calendar System

The brief

Design a Calendar System. Google Calendar-style events with recurrence, RSVPs and on-time reminders, using CDC for change notifications and a delay queue for reminders. Work from the scoping questions below. State assumptions for any unspecified load, guarantee or target, then trace your design end to end. Explain one difficult case and a credible alternative; the worked example is a reference, not a required implementation.

• Set the scope: Which event recurrence rules and time zones must be supported? Who can create, edit, cancel and RSVP to an event?
• Define the contract: What happens when one occurrence of a recurring event is edited? How close to its due time must a reminder arrive?
• Test the boundaries: What should happen after a schedule change or a missed reminder?

Constraints

Explicit scope and guarantees

Resolve the scoping questions for a Calendar System. Separate stated behavior from assumptions, and identify what is outside your design.

Supported operating targets

Declare relevant volume, latency, freshness, quality or cost targets with units. Show calculations or an evaluation plan that can test them; unspecified targets are your assumptions, not hidden pass criteria.

Failure and boundary behavior

Explain how your guarantees hold in a difficult case relevant to this subject. Address: How close to its due time must a reminder arrive? What should happen after a schedule change or a missed reminder?

What to cover

1. 01

   Scope and behavior contract

   Identify users, required behavior and exclusions. Answer: Which event recurrence rules and time zones must be supported? Who can create, edit, cancel and RSVP to an event?

2. 02

   State and interfaces

   Define the information owned by the system and the inputs, outputs and errors at its boundaries. Resolve: What happens when one occurrence of a recurring event is edited? How close to its due time must a reminder arrive?

3. 03

   Capacity and operating targets

   Estimate the dominant workload and resource demand with units and explicit assumptions. For a learned system, also state how quality is measured and what data is available.

4. 04

   Architecture and central flow

   Draw or describe the responsibilities needed for a Calendar System. Trace a representative request, event or job from its input to a visible result; identify durable state owners.

5. 05

   Failure and boundary walkthrough

   Walk through a difficult case step by step, including detection and recovery. Consider: What should happen after a schedule change or a missed reminder?

6. 06

   Tradeoffs and operations

   Compare a credible alternative using your chosen workload and guarantees. Explain a remaining risk, a signal to watch and when you would change the design.

Worked designs

Explore the architecture and decisions, then build on an example with Coach.

Official design

Design a Calendar System

Google Calendar-style events with recurrence, RSVPs and on-time reminders, using CDC for change notifications and a delay queue for reminders.

Explore the design

Review rubric

AI feedback uses these criteria. Scores are practice feedback.