Answer Key: Consensus & Leases

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Exercise 1: Choose Consensus

Question: When do you use consensus vs leases? What are the tradeoffs?

Answer

Use Consensus when: - Strong guarantees needed - No single point of failure acceptable - Can tolerate higher latency

Use Leases when: - Coordination needed but consensus too expensive - Time-based coordination sufficient - Lower latency required

Answer: Use consensus for strong guarantees, leases for lighter-weight coordination.

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Exercise 2: Handle Leader Failure

Question: Your consensus system loses its leader. How does it recover?

Answer

Recovery Process: 1. Detect: Detect leader failure (timeout) 2. Elect: Elect new leader (Raft/Paxos election) 3. Resume: Resume operations with new leader

Answer: Automatic leader election (Raft/Paxos), promote new leader, resume operations.

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Exercise 3: Design Leases

Question: Design a lease system for coordinating access to a shared resource.

Answer

Lease System: - Lease server: Manages leases - Lease duration: Time-limited (e.g., 30 seconds) - Renewal: Renew before expiry - Exclusivity: Only one holder at a time

Answer: Lease server manages leases, time-limited exclusivity, renewable leases.