Consensus, leader election, clocks, idempotency, retries, circuit breakers, microservices patterns and event-driven design.
39 cards · basic cards · AI-written, checked twice. Edit anything.
- What is the consensus problem in distributed systems?
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The requirement that all non-failed processes agree on a single value, even when some processes fail.- How does Raft simplify consensus compared to Paxos?
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Raft decomposes the problem into leader election, log replication, and safety, with one leader at a time managing all log entries.- What are the three roles in Paxos?
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Proposer (proposes values), Acceptor (votes on proposals), and Learner (learns the decided value).- What is a quorum in consensus algorithms?
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A majority subset of processes, typically more than half, whose agreement guarantees a consensus decision.- What is a term in Raft?
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A logical clock number that increments each time a new leader is elected, used to detect stale leaders and outdated information.- What is the split brain problem in leader election?
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A condition where network partitioning causes two separate leaders to exist, each believing it is the only legitimate leader.- How does Raft prevent split brain?
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By requiring a leader to have a quorum of followers committed to its leadership term, ensuring only one leader per term.- What is a heartbeat in Raft?
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A periodic message from the leader to followers indicating it is alive and maintaining leadership.- What happens when a follower does not receive a heartbeat?
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The follower times out, increments its term, and starts a new election by voting for itself and requesting votes from others.- What is election timeout in Raft?
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A randomized duration a follower waits before initiating an election if no heartbeat is received from the leader.- What is physical time?
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Actual wall-clock time measured by hardware clocks, which can drift and are not perfectly synchronized across systems.- What is a logical clock?
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A counter that orders events causally without requiring synchronized physical clocks, incrementing on local events and receiving messages.- How does Lamport timestamp order events?
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Each process maintains a counter; on any event it increments the counter, and on receiving a message it sets the counter to the max of its counter and the message's timestamp plus one.- What is a vector clock?
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A logical clock mechanism where each process maintains a vector of counters, one per process, tracking causal dependencies between all processes.- What is clock skew?
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The difference in time readings between different clocks in a distributed system due to drift and synchronization errors.
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