In distributed systems, which protocol is used to achieve consensus on the cluster state despite failures?

In distributed systems, which protocol is used to achieve consensus on the cluster state despite failures?

• A. Raft
• B. Paxos
• C. Two-Phase Commit
• D. Gossip protocol

Answer: (A)

Consensus on the cluster state in the presence of failures is achieved by a protocol that coordinates replicas to agree on a single, consistent history of state changes. Raft does this by design: it elects a leader to coordinate decisions, has the leader append new operations to its log, and replicates those log entries to followers. An entry is considered committed once a majority of nodes have written it, which provides resilience to failures because the information survives as long as a majority remains available. If the leader crashes, a new leader is elected and the system continues, with safety guarantees that once something is committed, it cannot be contradicted by future decisions. This combination of leader-based replication, majority quorums, and deterministic state progression makes Raft a practical and widely used choice for maintaining a consistent cluster state despite failures. Paxos is another rigorous consensus idea, but Raft is often chosen for its clarity and real-world practicality while delivering the same guarantees. Two-Phase Commit is about coordinating distributed transactions and can block if the coordinator fails, which isn’t suited for ongoing cluster state consensus. Gossip protocols spread information efficiently but do not provide the strong, guaranteed consensus on a single replicated state.

Consensus on the cluster state in the presence of failures is achieved by a protocol that coordinates replicas to agree on a single, consistent history of state changes. Raft does this by design: it elects a leader to coordinate decisions, has the leader append new operations to its log, and replicates those log entries to followers. An entry is considered committed once a majority of nodes have written it, which provides resilience to failures because the information survives as long as a majority remains available. If the leader crashes, a new leader is elected and the system continues, with safety guarantees that once something is committed, it cannot be contradicted by future decisions. This combination of leader-based replication, majority quorums, and deterministic state progression makes Raft a practical and widely used choice for maintaining a consistent cluster state despite failures.

Paxos is another rigorous consensus idea, but Raft is often chosen for its clarity and real-world practicality while delivering the same guarantees. Two-Phase Commit is about coordinating distributed transactions and can block if the coordinator fails, which isn’t suited for ongoing cluster state consensus. Gossip protocols spread information efficiently but do not provide the strong, guaranteed consensus on a single replicated state.