Zero-Downtime Migration RFC

Template Overview

Migrating large-scale databases or fundamental storage engines without service disruption requires rigorous systems engineering and thorough peer review. The Zero-Downtime Migration RFC template outlines architectural proposals, dual-write state machines, backfill throughput models, and fail-safe rollback protocols in sovereign Markdown.

Markdown Template Structure

Copy the block below or click Download .md File to add this template directly to your personal vault:

---
title: "RFC: Zero-Downtime Migration of [System / Data Store]"
date: [YYYY-MM-DD]
author: "[[Staff Infrastructure Engineer]]"
sponsors: ["[[Principal Architect]]", "[[VP Engineering]]"]
status: "[Draft / Under Review / Approved / Implemented / Superseded]"
target_implementation_quarter: "[Q1 / Q2 / Q3 2026]"
tags: [rfc, engineering, database, migration, architecture, reliability]
---

# RFC: Zero-Downtime Migration — [System Name]

## 1. Problem Statement & Motivation
- **Current Architecture:** Monolithic legacy database experiencing table lock contention during peak concurrent writes.
- **Target Architecture:** Distributed sharded database engine with local SQLite FTS5 search indexing.
- **Success Criteria:** Zero planned customer downtime (0.00% downtime), zero data loss, sub-20ms P99 query latency.

## 2. Migration Architecture & Phased Strategy

Zero-Downtime Migration Sequence: Phase 1: Dual-Write (Source Primary + Target Shadow) Phase 2: Historical Asynchronous Data Backfill & CDC Phase 3: Automated Read-Shadowing & Checksum Parity Validation Phase 4: Traffic Canary Shift (1% -> 10% -> 50% -> 100%) Phase 5: Source Deprecation & Teardown

## 3. Data Integrity & Checksum Verification
| Verification Dimension | Metric / Tool | Parity Target | Action on Drift |
|---|---|---|---|
| **Row Checksums** | SHA-256 hash per primary key row | 100.000% Match | Halt shift; log mismatch |
| **Replication Lag** | CDC Kafka offset lag | < 50 milliseconds | Throttle backfill worker pool |
| **Write Latency Regress**| P99 write latency measurement | <= 24 milliseconds | Revert canary traffic |

## 4. Rollback & Disaster Recovery Protocol
- **Immediate Rollback Trigger:** If error rate on target system exceeds 0.05% or replication lag exceeds 500 ms for longer than 60 seconds.
- **Rollback Procedure:** Reverse feature flag instantly, directing 100% of read and write traffic back to legacy primary. Target becomes read-only replica.

## 5. Architectural Review Sign-Offs
- [ ] [[Principal Architect]] Approve dual-write concurrency locking model.
- [ ] [[Security Lead]] Validate encryption key rotation during data backfill.
- [ ] [[VP Engineering]] Authorize execution schedule.

Filled Real-World Example

Here is a realistic example demonstrating how this template captures actual deliberations:

---
title: "RFC: Local SQLite Storage Migration"
date: 2026-10-10
author: "[[Vikram Sethi]]"
sponsors: ["[[Marcus Vance]]", "[[Dr. Elena Rostova]]"]
status: "Approved"
target_implementation_quarter: "Q4 2026"
tags: [rfc, engineering, database, migration, architecture, reliability]
---

# RFC: Local SQLite Storage Migration

## 1. Executive Summary
Vikram Sethi proposed migrating search indexing from an in-memory inverted index to an on-disk SQLite FTS5 database with Porter stemming. The architecture guarantees zero memory bloat on large 100k-note vaults.

## 2. Review Verdict
Marcus Vance and Elena Rostova approved the proposal, noting that SQLite's Write-Ahead Log (WAL) mode provides crash-resilient ACID guarantees with zero network reliance.

## 3. Schedule
Implementation scheduled across Sprints 42 and 43.

When to Use and When to Avoid

When to Use

• Use prior to undertaking high-risk database migrations, data store replacements, or schema overhauls.
• Use to establish consensus across infrastructure, security, and application engineering teams.
• Use to document rigorous dual-write architectures, parity checks, and automated rollback triggers.

When to Avoid

• Avoid for minor backward-compatible database schema column additions.
• Avoid for non-technical product marketing plans.

On-Device AI Integration

Summarize your recording in Oyma with this local instruction:

Summarize the migration RFC review meeting recording:
1. Outline the problem statement, proposed migration architecture, and phased cutover plan.
2. Detail data verification checksum strategies, replication lag tolerances, and rollback triggers.
3. Record architectural critiques raised, modifications requested, and formal approval sign-offs.
Output in clean, structured Markdown.

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