Key Questions:
- "What's the scale? How many locks and clients?"
- "Do we need strong consistency or is eventual consistency okay?"
- "What's the acceptable latency for lock operations?"
- "How do we handle network partitions?"
- "Do we need leader election capabilities?"

"I'll design a Raft-based distributed locking system:

1. Architecture:
   - 5-node cluster for fault tolerance
   - Raft consensus for state replication
   - Leader handles all writes
   - Followers can serve reads

2. Key Components:
   - Lock service (acquire/release)
   - Session management (heartbeats)
   - Watch service (notifications)
   - Raft consensus layer

3. Safety Guarantees:
   - Mutual exclusion via consensus
   - Fencing tokens for correctness
   - Quorum-based decisions
   - No split-brain"

"Raft ensures all nodes agree on lock state:

1. Leader Election:
   - Nodes vote for leader
   - Majority wins
   - Term numbers prevent conflicts

2. Log Replication:
   - Leader appends to log
   - Replicates to followers
   - Commits when majority acknowledges

3. Safety:
   - Only committed entries applied
   - Leader has all committed entries
   - State machine deterministic"

"Critical edge cases:

1. Client Failure:
   - Session timeout detects failure
   - Automatic lock release
   - Prevents deadlocks

2. Network Partition:
   - Majority partition continues
   - Minority stops serving writes
   - Automatic recovery on heal

3. Leader Failure:
   - New election triggered
   - New leader elected in <5 seconds
   - No data loss (committed entries safe)"

✓ Strong consistency via Raft
✓ Mutual exclusion guaranteed
✓ Fencing tokens prevent races
✓ Session-based failure detection
✓ Quorum-based decisions

✓ Fault tolerance (N-1)/2 failures
✓ Automatic failover
✓ No split-brain
✓ Monitoring and alerting
✓ Operational simplicity

"We'll use Redis for distributed locks"
→ Weak consistency, not suitable for critical locks

"Clocks are synchronized so we can use timestamps"
→ Clock skew causes correctness issues

"We don't need consensus, eventual consistency is fine"
→ Locks require strong consistency

"We'll use Raft consensus for strong consistency"
→ Industry-proven approach

"Fencing tokens prevent stale lock holders"
→ Shows understanding of correctness

"Quorum-based decisions ensure safety"
→ Demonstrates distributed systems knowledge