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tarantool-etcd-boq Learner: raft state machine (follower/learner subset) Lined Up

status: open P2 task milestone:m5-clustering
bd update tarantool-etcd-boq --claim bd close tarantool-etcd-boq
Created byEugene Blikh
Ownerbigbes@gmail.com
Created2026-05-20T06:45:15Z
Updated2026-07-17T14:27:37Z
Description
Minimal raft state machine for a non-voting learner. Track currentTerm, commitIndex, lastApplied, and the membership ConfState. Handle: MsgApp (append entries, advance commit), MsgHeartbeat (advance commit, reply), MsgSnap (hand to snapshot phase). Explicitly DROP/reject MsgVote/MsgPreVote and never campaign or transition to candidate/leader (learners can't vote or be elected). Apply ConfChange entries to track membership (including our own promotion away from learner -> would flip behavior, out of v1 scope). No proposal path. This is the brain that decides which entries are committed and ready to apply; the apply loop is a separate phase.
Notes
We are NOT reimplementing etcd's full raft — only the receive/commit/apply path a learner needs. Election, log compaction-on-leader, ReadIndex coordination all out of scope.

Depends on

  • tarantool-etcd-axs — Learner: rafthttp peer transport over nghttp2 blocks open
  • tarantool-etcd-cnj — [epic] Raft-learner replica — join an etcd cluster as a non-voting member parent-child open
  • tarantool-etcd-4yb — Learner: raftpb + InternalRaftRequest proto schemas blocks open

Depended on by

  • tarantool-etcd-6js — Learner: apply loop — InternalRaftRequest -> existing handlers blocks

Prerequisite chain — everything this waits on, transitively

  • tarantool-etcd-axs — Learner: rafthttp peer transport over nghttp2 blocks open
  • tarantool-etcd-umc — Learner: config block + role plumbing blocks open
  • tarantool-etcd-cnj — [epic] Raft-learner replica — join an etcd cluster as a non-voting member parent-child open
  • tarantool-etcd-7ey — Replica route: connect as read-only replica to an existing etcd cluster related open
  • tarantool-etcd-16d — Implement Maintenance.Snapshot RPC (streaming DB snapshot) related open
  • tarantool-etcd-4yb — Learner: raftpb + InternalRaftRequest proto schemas blocks open

Unblocks — everything waiting on this, transitively

  • tarantool-etcd-6js — Learner: apply loop — InternalRaftRequest -> existing handlers blocks open
  • tarantool-etcd-q5f — Learner: snapshot receive (bbolt parse + bucket translation) blocks open
  • tarantool-etcd-zkg — Learner: conformance — join real etcd cluster, assert log replication blocks open
  • tarantool-etcd-ovo — Learner: durable applied_index (WAL-equivalent for restart) blocks open

No comments.

  • Eugene Blikh created the issue · 2026-05-20T09:45:15Z
  • Eugene Blikh added dependency on tarantool-etcd-axs · 2026-05-20T09:47:29Z
  • Eugene Blikh added under epic tarantool-etcd-cnj · 2026-05-20T09:47:29Z
  • Eugene Blikh tarantool-etcd-6js now depends on this · 2026-05-20T09:47:29Z
  • Eugene Blikh added dependency on tarantool-etcd-4yb · 2026-05-20T09:47:29Z
  • Eugene Blikh added label milestone:m5-clustering · 2026-05-21T14:37:39Z
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id tarantool-etcd-boq
content_hash 78f7ab0f980e3e418ac85b10e54290632eb565a339b43e58c52e1512d179539a
title Learner: raft state machine (follower/learner subset)
description Minimal raft state machine for a non-voting learner. Track currentTerm, commitIndex, lastApplied, and the membership ConfState. Handle: MsgApp (append entries, advance commit), MsgHeartbeat (advance commit, reply), MsgSnap (hand to snapshot phase). Explicitly DROP/reject MsgVote/MsgPreVote and never campaign or transition to candidate/leader (learners can't vote or be elected). Apply ConfChange entries to track membership (including our own promotion away from learner -> would flip behavior, out of v1 scope). No proposal path. This is the brain that decides which entries are committed and ready to apply; the apply loop is a separate phase.
design
acceptance_criteria
notes We are NOT reimplementing etcd's full raft — only the receive/commit/apply path a learner needs. Election, log compaction-on-leader, ReadIndex coordination all out of scope.
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created_at 2026-05-21T14:37:39Z