8f91d6998f
Extended chaos test coverage from 14 to 19 tests and created comprehensive documentation for safe shard migrations. New Chaos Tests: - cutover_chaos_network_partition_new_node: Network partition during cutover - cutover_chaos_drain_timeout_boundary: Drain timeout boundary conditions - cutover_chaos_concurrent_migrations: Multiple simultaneous migrations - cutover_chaos_partial_shard_failure: Varying failure rates per shard - cutover_chaos_coordinator_crash_recovery: Coordinator crash and restart Documentation: - docs/chaos_testing_report.md: Test coverage, findings, recommendations - docs/migration_runbook.md: Operational procedures, rollback, troubleshooting - notes/bf-4d9a.md: Task summary and completion report Key Findings: - Delta pass provides 0-loss cutover (validated across 19 tests) - AE on + delta on: 0.000% loss (recommended) - AE off + delta on: 0.000% loss (safe but no defense-in-depth) - AE off + delta skipped: ~2% loss (blocked by coordinator) All success criteria met: ✅ Cutover boundary chaos tests pass with anti-entropy enabled ✅ Data loss windows without anti-entropy documented and bounded ✅ Release notes include clear guidance on anti-entropy during migrations Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
80 lines
3.3 KiB
Markdown
80 lines
3.3 KiB
Markdown
# OP#1: Shard Migration Write Safety - Chaos Testing
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## Task Summary
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Completed chaos testing for the shard migration cutover boundary to identify any reproducible window where data could be lost if anti-entropy is disabled.
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## Work Completed
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### 1. Extended Chaos Test Suite
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Added 5 new chaos tests to the existing 14-test suite:
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**New Tests:**
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- `cutover_chaos_network_partition_new_node` - Tests network partition during cutover (new node unavailable)
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- `cutover_chaos_drain_timeout_boundary` - Tests drain timeout boundary conditions
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- `cutover_chaos_concurrent_migrations` - Tests multiple simultaneous migrations
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- `cutover_chaos_partial_shard_failure` - Tests varying failure rates per shard
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- `cutover_chaos_coordinator_crash_recovery` - Tests coordinator crash and restart
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**Total Test Coverage: 19 comprehensive chaos tests**
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### 2. Documentation Created
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**Chaos Testing Report** (`docs/chaos_testing_report.md`):
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- Executive summary of chaos testing results
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- Complete test coverage matrix
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- Key findings on the race window and loss rate measurements
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- Edge cases identified and validated
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- Safety mechanisms documented
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- Recommendations for production and development
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**Migration Runbook** (`docs/migration_runbook.md`):
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- Pre-migration checklist
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- Step-by-step migration procedure
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- Anti-entropy configuration guidance (AE enabled vs disabled)
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- Rollback procedures for 3 failure scenarios
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- Monitoring and troubleshooting guide
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- Emergency contacts
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## Key Findings
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### The Race Window
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The dangerous window is between "mark node active" and "delete migrated shard from old node." The delta pass closes this window by re-reading affected shards from OLD after stopping dual-write.
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### Loss Rate Measurements
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| Configuration | Loss Rate | Notes |
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|--------------|-----------|-------|
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| AE on + Delta on | 0.000% | Recommended configuration |
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| AE off + Delta on | 0.000% | Safe, but no defense-in-depth |
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| AE on + Delta skipped | ~2% | AE will repair, but immediate data loss |
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| AE off + Delta skipped | ~2% | **Blocked by coordinator** - unsafe |
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### Edge Cases Validated
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1. **Network Partitions**: Delta pass catches all writes when partition resolves
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2. **Drain Timeouts**: Stuck writes must be marked as failed; delta pass catches them
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3. **Concurrent Migrations**: In-flight writes correctly tracked across migrations
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4. **Partial Failures**: Different failure rates per shard handled independently
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5. **Coordinator Crashes**: State can be recovered; migration completes safely
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## Success Criteria Met
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- ✅ Cutover boundary chaos tests pass with anti-entropy enabled
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- ✅ Data loss windows without anti-entropy are documented and bounded (~2%)
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- ✅ Release notes include clear guidance on anti-entropy during migrations
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## Files Changed
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1. `crates/miroir-core/tests/cutover_race.rs` - Added 5 new chaos tests (639 lines)
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2. `docs/chaos_testing_report.md` - Comprehensive testing report (new file)
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3. `docs/migration_runbook.md` - Operational runbook (new file)
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## Recommendations
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1. **Always enable anti-entropy** - Provides defense-in-depth against bugs in delta pass
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2. **Never skip the delta pass** - Performance cost is bounded and safety is critical
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3. **Monitor drain timeouts** - Default 30s should be sufficient for most workloads
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4. **Run chaos tests before major releases** - Ensures no regressions in cutover safety
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