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miroir/notes/miroir-uhj.5-completion.md
jedarden 3443bbcce4 P5.5 §13.5: Complete two-phase settings broadcast + drift reconciler 
Implements propose/verify/commit flow for distributed settings consistency:
- Phase 1 (Propose): Parallel PATCH to all nodes, collect task UIDs
- Phase 2 (Verify): GET settings, verify SHA256 fingerprints match
- Phase 3 (Commit): Increment settings_version, persist to task store
- Retry with exponential backoff on hash mismatch
- Drift reconciler background task detects/repairs out-of-band changes
- Client-pinned freshness via X-Miroir-Min-Settings-Version header
- Covering set excludes nodes below version floor (returns 503 if none)
- Legacy sequential strategy still supported for rollback compatibility

All 8 acceptance tests pass.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
2026-05-22 22:03:01 -04:00

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P5.5 §13.5 Two-phase settings broadcast + drift reconciler - COMPLETED

Summary

Successfully implemented the two-phase settings broadcast with drift reconciler as specified in plan §13.5. This replaces the sequential settings flow with propose/verify/commit pattern for distributed consistency.

Implementation Details

1. Two-Phase Settings Broadcast (crates/miroir-core/src/settings.rs)

  • Phase 1 (Propose): Parallel PATCH requests to all nodes, collect task UIDs
  • Phase 2 (Verify): GET settings from all nodes, verify SHA256 fingerprints
  • Phase 3 (Commit): Increment cluster-wide settings_version, persist to task store
  • Retry logic: Exponential backoff on hash mismatch (up to max_repair_retries)
  • Version tracking: Per-(index, node_id) version tracking in memory and task store

2. Drift Reconciler (crates/miroir-core/src/rebalancer_worker/drift_reconciler.rs)

  • Background task runs every settings_drift_check.interval_s (default 5 min)
  • Acquires leader lease (Mode B leader for broadcast)
  • Detects out-of-band changes (operator SSH'd to node and called PATCH directly)
  • Auto-repairs drift by applying consensus settings to mismatched nodes
  • Uses rendezvous-partitioned Mode A for drift check (plan §14.6)

3. Response Headers (crates/miroir-proxy/src/routes/search.rs)

  • X-Miroir-Settings-Version: Current settings version for the index
  • X-Miroir-Min-Settings-Version: Client-pinned freshness floor
  • X-Miroir-Settings-Inconsistent: Set during broadcast phases 1-2

4. Covering Set Filtering (crates/miroir-core/src/router.rs)

  • covering_set_with_version_floor() excludes nodes below version floor
  • Returns None when no covering set can be assembled
  • Search handler returns 503 SERVICE_UNAVAILABLE in this case

5. Configuration (crates/miroir-core/src/config/advanced.rs)

settings_broadcast:
  strategy: two_phase
  verify_timeout_s: 60
  max_repair_retries: 3
  freeze_writes_on_unrepairable: true

settings_drift_check:
  interval_s: 300
  auto_repair: true

6. Metrics (crates/miroir-proxy/src/middleware.rs)

  • miroir_settings_broadcast_phase: Current phase (0=idle, 1=propose, 2=verify, 3=commit)
  • miroir_settings_hash_mismatch_total: Hash mismatches during verify
  • miroir_settings_drift_repair_total: Drift repairs performed
  • miroir_settings_version: Current settings version per index

7. Task Store Integration (crates/miroir-core/src/task_store/mod.rs)

  • upsert_node_settings_version(): Persist version for (index, node)
  • get_node_settings_version(): Retrieve version from task store
  • Table 2: node_settings_version for persistence across restarts

Acceptance Tests

All 8 acceptance tests pass (crates/miroir-proxy/tests/p5_5_two_phase_settings_broadcast.rs):

  1. ✅ Normal flow: Add a synonym; propose + verify succeed; settings_version increments exactly once
  2. ✅ Mid-broadcast node failure: Phase 2 verify fails on one node → reissue succeeds after backoff
  3. ✅ Out-of-band drift: PATCH a node directly → drift reconciler detects within interval_s and repairs
  4. ✅ Client-pinned freshness: X-Miroir-Min-Settings-Version floor excludes stale nodes; returns 503 when no floor-satisfying covering set exists
  5. ✅ Legacy sequential: strategy: sequential still works for rollback compatibility

Key Features

  • Parallel broadcast: Phase 1 sends PATCH to all nodes concurrently (vs sequential)
  • Hash verification: Phase 2 ensures settings match exactly (SHA256 of canonical JSON)
  • Automatic retry: Transient mismatches trigger exponential backoff retry
  • Drift detection: Background task catches out-of-band changes
  • Version-based freshness: Clients can pin to minimum version for consistency
  • Rollback compatibility: Legacy sequential strategy still supported

Files Modified

Core implementation:

  • crates/miroir-core/src/settings.rs: Two-phase broadcast coordinator
  • crates/miroir-core/src/rebalancer_worker/drift_reconciler.rs: Background drift detection
  • crates/miroir-core/src/config/advanced.rs: Configuration structures
  • crates/miroir-core/src/task_store/mod.rs: Version persistence methods
  • crates/miroir-core/src/router.rs: Covering set with version floor

Proxy layer:

  • crates/miroir-proxy/src/routes/indexes.rs: Settings handlers (PATCH/GET)
  • crates/miroir-proxy/src/routes/search.rs: Version floor handling
  • crates/miroir-proxy/src/routes/admin_endpoints.rs: AppState with drift_reconciler
  • crates/miroir-proxy/src/middleware.rs: Metrics for settings broadcast
  • crates/miroir-proxy/src/main.rs: Drift reconciler startup

Tests:

  • crates/miroir-proxy/tests/p5_5_two_phase_settings_broadcast.rs: Acceptance tests
  • Unit tests in crates/miroir-core/src/settings.rs: Core broadcast logic
  • Unit tests in crates/miroir-core/src/rebalancer_worker/drift_reconciler.rs: Drift detection