## Round 1 - Coding ## Problem Design a `LeaderFollower` system where one node acts as the leader and all others are followers. The leader accepts writes; followers replicate state and can serve reads. ```python class Node: def __init__(self, node_id: str): ... class LeaderFollowerCluster: def __init__(self, nodes: list[str]): ... def elect_leader(self) -> str: ... def write(self, key: str, value: str) -> bool: ... def read(self, node_id: str, key: str) -> str: ... def fail_node(self, node_id: str) -> str: # returns new leader if applicable ... ``` ## Example ``` cluster = LeaderFollowerCluster(["A", "B", "C"]) cluster.elect_leader() -> "A" cluster.write("x", "10") -> True cluster.read("B", "x") -> "10" # replicated cluster.fail_node("A") -> "B" # B becomes new leader cluster.write("x", "20") -> True cluster.read("C", "x") -> "20" ``` ## Follow-ups 1. How do you handle a write that arrives while a leader election is in progress? 2. What consistency guarantees does a follower read provide? How would you support read-your-writes? 3. How do you detect a leader failure — heartbeat timeout, explicit signal, or quorum-based? 4. How does your design change if the cluster has 100 nodes?

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Leader-Follower System: Implement a Primary/Replica Coordination Module

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Round 1 - Coding Problem Design a LeaderFollower system where one node acts as the leader and all others are followers. The leader accepts writes; followers replicate state and can serve reads. Example Follow-ups How do you handle a write that arrives while a leader election is in progress? What consistency guarantees does a follower read provide? How would you support read-your-writes? How do you detect a leader failure — heartbeat timeout, explicit signal, or quorum-based? How does your design…

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Leader-Follower System: Implement a Primary/Replica Coordination Module

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