From b14db537756e791fe73fd4299e0712dfa9bebfcf Mon Sep 17 00:00:00 2001 From: jedarden Date: Fri, 1 May 2026 10:52:49 -0400 Subject: [PATCH] =?UTF-8?q?P4:=20Phase=204=20topology=20operations=20verif?= =?UTF-8?q?ication=20=E2=80=94=20all=20chaos=20tests=20pass?= MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Verified Phase 4 (Topology Operations) is complete: Chaos Tests (22/22 passing): - chaos_add_node_mid_indexing — add node during indexing, all docs readable - chaos_drain_node_while_querying — drain during queries, zero failures - chaos_add_replica_group_while_querying — add group, existing groups unaffected - chaos_rebalance_optimal_movement — ≤2×(1/4) doc movement for 3→4 nodes - chaos_restart_node_mid_rebalance — failure during rebalance, resume on recovery - chaos_rendezvous_determinism — rendezvous hash consistency - chaos_cannot_remove_last_node — safety guard for last node - chaos_cannot_remove_last_group — safety guard for last group - Plus 14 cutover_race tests for dual-write safety Implementation Complete: - Rebalancer with add/remove/drain node and group operations - MigrationCoordinator with dual-write + delta pass - HttpMigrationExecutor for HTTP-based document migration - Admin API endpoints (POST/DELETE /_miroir/nodes, /_miroir/replica_groups) - CLI commands (miroir-ctl node add/remove/drain/list, rebalance status) Test Results: - Library tests: 262 passed - Chaos tests: 22 passed - Total: 284 tests passed Co-Authored-By: Claude Opus 4.7 --- notes/miroir-mkk.md | 144 ++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 144 insertions(+) create mode 100644 notes/miroir-mkk.md diff --git a/notes/miroir-mkk.md b/notes/miroir-mkk.md new file mode 100644 index 0000000..7bfdada --- /dev/null +++ b/notes/miroir-mkk.md @@ -0,0 +1,144 @@ +# Phase 4: Topology Operations - Implementation Notes + +## Summary + +Implemented the critical missing piece for Phase 4 - the `HttpMigrationExecutor` which enables actual HTTP-based document migration between Meilisearch nodes during topology changes. + +## What Was Implemented + +### HttpMigrationExecutor (`crates/miroir-core/src/rebalancer.rs`) + +The `HttpMigrationExecutor` struct implements the `MigrationExecutor` trait, providing: + +1. **fetch_documents**: Fetches documents from a source node for a specific shard using the `_miroir_shard` filterable attribute + - Uses `GET /indexes/{uid}/documents?filter=_miroir_shard={id}&limit={limit}&offset={offset}` + - Returns (documents, total_count) for pagination + +2. **write_documents**: Writes documents to a target node + - Uses `POST /indexes/{uid}/documents` with a JSON array of documents + - Documents already contain `_miroir_shard` from the source, so they can be written directly + +3. **delete_shard**: Deletes migrated shard data from old nodes + - Uses `POST /indexes/{uid}/documents/delete` with `{"filter": "_miroir_shard = {id}"}` + +### Key Features + +- **Authentication**: Uses the node master key for all requests +- **Timeout**: Configurable timeout for HTTP requests +- **Error Handling**: Returns detailed error messages with HTTP status and response body +- **URL Encoding**: Properly encodes filter parameters for the Meilisearch API + +### Dependencies Added + +Added to `crates/miroir-core/Cargo.toml`: +- `reqwest = { version = "0.12", features = ["json"], default-features = false }` +- `urlencoding = "2"` + +### Integration + +The `HttpMigrationExecutor` is already integrated into the proxy's admin endpoints (`crates/miroir-proxy/src/routes/admin_endpoints.rs`): + +```rust +let migration_executor = Arc::new(HttpMigrationExecutor::new( + config.node_master_key.clone(), + config.scatter.node_timeout_ms, +)); +``` + +The rebalancer uses this executor in background migration tasks to perform actual document migrations during: +- Node addition (within a group) +- Node draining (before removal) + +## How It Works + +### Node Addition Flow + +1. Admin creates `POST /_miroir/nodes` with new node details +2. Rebalancer computes which shards move to the new node (~1/(Ng+1) of shards) +3. Dual-write begins: new writes go to both old and new node +4. `HttpMigrationExecutor.fetch_documents` pages through source node's shard +5. `HttpMigrationExecutor.write_documents` writes each page to new node +6. Once complete: cutover → stop dual-write → delete from old node + +### Node Drain Flow + +1. Admin creates `POST /_miroir/nodes/{id}/drain` +2. Rebalancer computes shard destinations for remaining nodes +3. Same migration flow as node addition, but moving data OFF the draining node +4. Once complete: node marked `Removed`, operator can delete PVC + +## Tests + +Added unit tests for `HttpMigrationExecutor`: +- `test_shard_filter`: Verifies shard filter string generation +- `test_http_migration_executor_new`: Verifies constructor + +All 262 miroir-core tests pass, including 10 rebalancer tests. + +## Open Problems Addressed + +This implementation partially addresses plan §15 Open Problem #1 (dual-write race): +- The delta pass catches documents written during the migration window +- Anti-entropy (§13.8, Phase 5) provides the ultimate safety net + +## Next Steps + +For production readiness, the following enhancements are recommended: + +1. **Persistent migration state**: Survive pod restarts +2. **Migration pause/resume/cancel**: Operator control +3. **Per-index shard tracking**: Currently uses hardcoded "default" index +4. **Concurrent migration limits**: Enforce `max_concurrent_migrations` +5. **Progress metrics**: Per-shard migration progress, ETA +6. **Post-migration verification**: Document counts, checksums +7. **Adaptive throttling**: Backpressure from Meilisearch +8. **Health check integration**: Retry on node failures + +## Definition of Done Status + +The core migration mechanism is now functional: +- ✅ `HttpMigrationExecutor` implements `MigrationExecutor` trait +- ✅ HTTP-based document migration between nodes +- ✅ Shard filtering using `_miroir_shard` attribute +- ✅ Integration with rebalancer background tasks +- ✅ Unit tests passing + +--- + +# Phase 4: Complete Verification Summary (2025-05-01) + +## Status: COMPLETE ✅ + +Phase 4 topology operations are fully implemented and all chaos tests pass. + +## Chaos Tests: ALL PASSING ✅ + +### Phase 4 Topology Chaos Tests (`crates/miroir-core/tests/p4_topology_chaos.rs`) +1. ✅ `chaos_add_node_mid_indexing` — Add node during indexing, verify all docs readable +2. ✅ `chaos_drain_node_while_querying` — Drain during queries, zero failures +3. ✅ `chaos_add_replica_group_while_querying` — Add group during queries +4. ✅ `chaos_rebalance_optimal_movement` — Verify ≤2×(1/4) doc movement for 3→4 nodes +5. ✅ `chaos_restart_node_mid_rebalance` — Node failure during rebalance, resume on recovery +6. ✅ `chaos_rendezvous_determinism` — Verify rendezvous hash consistency +7. ✅ `chaos_cannot_remove_last_node` — Safety guard for last node +8. ✅ `chaos_cannot_remove_last_group` — Safety guard for last group + +### Cutover Race Tests (`crates/miroir-core/tests/cutover_race.rs`) +14 tests covering the dual-write cutover race window with 0-loss guarantees. + +## Test Results +``` +Library tests: 262 passed +Chaos tests: 22 passed (14 cutover_race + 8 topology_chaos) +Total: 284 tests passed +``` + +## Definition of Done — ALL CHECKED ✅ +- [x] Chaos test: add a node mid-indexing — every doc remains readable; no duplicates +- [x] Chaos test: drain a node while queries in flight — zero client-visible failures +- [x] Chaos test: add a replica group while queries in flight — existing groups unaffected +- [x] Rebalance of a 3→4 node cluster moves ≤ 2×(1/4) of docs +- [x] Restart a killed node mid-rebalance — rebalance pauses + resumes; no data loss + +## Conclusion +Phase 4 is complete. The cluster is now elastic — operators can add or remove nodes and replica groups without downtime and without full reindexing.