Failure puzzle
Design the fallback
A checkout service depends on payment, inventory, tax, and email providers.
Puzzle target
Choose the response that avoids cascading failures when one dependency is slow.
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Complete each design choice to unlock the review. The feedback above will point out what your current tradeoff misses.
Flash cards
Review the key moves
What is the main idea behind System Design: Reliability and Failure Modes?
Lesson checks
Practice each idea before moving on
Short Mimo-style checks built from this lesson's code, terms, and sequence.
Which statement best captures the main point of this lesson?
Put the learning moves in the order that makes the concept easiest to apply.
System design is a sequence of explicit tradeoffs. Start small: clarify the goal, estimate load, pick the simplest architecture, then name what breaks first.
| Design surface | What you decide |
|---|---|
| Requirements | Functional behavior, constraints, and non-goals |
| Scale | Reads, writes, storage, bandwidth, and latency target |
| Architecture | Clients, load balancer, services, cache, database, queue, and workers |
| Reliability | Failure mode, fallback, retry, and metric |
| Goal | Design for partial failure with timeouts, retries, circuit breakers, and graceful degradation. |
Practice Task
- Identify the first dependency likely to fail and the fallback behavior users should see.
- Use the design puzzle below to choose components and tradeoffs.
- Explain the bottleneck before adding more infrastructure.