Practice leader election vocabulary: Raft leader leases, split-brain scenarios, election timing, Zookeeper-based election, and Bully algorithm language.
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In Raft, 'the leader holds the lease' means:
A Raft leader lease is a time-bounded guarantee that the leader is the only node serving as leader. The lease prevents a partitioned node that thinks it is still the leader from processing requests after losing quorum contact.
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What is 'split-brain during leader election'?
Split-brain occurs when a network partition isolates nodes such that two separate groups each elect their own leader. Both leaders accept writes, creating conflicting state. Preventing split-brain is a core motivation for quorum-based consensus protocols.
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A monitoring alert says 'the cluster elected a new leader in 200ms.' This 200ms represents the:
Leader election time is the duration from when a follower detects the leader is unresponsive (election timeout) to when a new leader wins a majority vote and begins serving. A 200ms election time means only 200ms of unavailability — good for high-availability systems.
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What does 'using Zookeeper for leader election' mean in practice?
ZooKeeper leader election uses ephemeral sequential znodes: each candidate creates a sequential node under a path; the candidate with the lowest sequence number is the leader. Other candidates watch the node just above them — when it disappears, the next candidate takes over.
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In the Bully algorithm for leader election, the 'bully' is:
The Bully algorithm elects the node with the highest process ID as leader. Any node noticing a leader failure starts an election by messaging all nodes with higher IDs. If none respond, it declares itself leader. If a higher-ID node responds, it takes over the election.