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Step 04 of 8 2-4 weeks· advanced

Step 4: Set Up Dual-Write or CDC

Keep the target DB in sync with source as the migration progresses. Choose dual-write, CDC (Debezium / DMS), or trickle-batch based on downtime tolerance and tooling.

What you're doing in this step

For zero-downtime migration, target must stay current with source. Pick one: (A) dual-write from app, (B) CDC streaming, (C) periodic batch sync. Deploy the chosen sync mechanism, monitor lag, set drift thresholds and stop conditions.

Recommended prompts

Use one of these to do the work in your IDE

Open the template to read it in full. Click Copy prompt to grab it (with your stack values pre-filled where they apply) — then paste into Claude Code, Cursor, or wherever you build.

Primary recommendation 1-2 days

Data Migration Plan

Plan a safe data migration: schema mapping, ETL strategy, dual-write or one-shot, validation, and cutover with rollback.

View template
Template· Template 0.5 day

Feature Flag Rollout Strategy for Migrations

Use feature flags to safely route traffic between legacy and new systems during migration with controlled rollout and instant rollback.

Use this when: You want to feature-flag the dual-read / dual-write rollout per app

View template
Recommended skills

Drop these into Claude Code for this phase

Skills auto-trigger on the right kind of request. Install once; they apply to every prompt that fits.

Skill· Skill 5 min setup

Compatibility Layer Generator Skill

Claude Code skill that generates adapters, shims, and proxies for incremental coexistence between legacy and new systems.

claude-codedotnet
View skill
Skill· Skill 5 min setup

Data Validation Skill

Claude Code skill that compares old and new system outputs for parity — running validation queries on both DBs and reporting drift.

claude-codesql
View skill
Skill· Skill 5 min setup

Database Migration Skill

Claude Code skill that generates safe forward and reverse migrations with transaction-wrapping, idempotency, and zero-downtime patterns.

claude-code
View skill
Recommended MCP configs

Wire these tools into Claude Code first

MCP servers give Claude Code direct access to external systems (Jira, browsers, databases). Configure once.

MCP config· MCP config 10 min setup

Postgres MCP for Evoke

Pre-configured Postgres MCP server for Claude Code — schema inspection and read-only queries to make database work safer and faster.

claude-codemcppostgres
View config
MCP config· MCP config 5 min setup

Filesystem MCP for Evoke

Pre-configured filesystem MCP server for Claude Code — safe, scoped read/write access to project files.

claude-codemcp
View config
MCP config· MCP config 10 min setup

Azure DevOps MCP for Evoke

Pre-configured Azure DevOps MCP server for Claude Code — work items, repos, PRs, and pipelines from chat.

claude-codemcp
View config
When you're done

Verify these in your own work before moving on

This is a checklist for you to mentally tick off in your repo and IDE — the site doesn't track it, you do.

  • Sync mechanism deployed (dual-write code, CDC pipeline, or batch jobs)
  • Sync is monitored (lag metric, error rate, drift detection)
  • Validation runs continuously (counts and sums match between source and target)
  • Stop conditions defined (when to halt sync if drift exceeds threshold)
  • Sync can be paused / resumed safely
Common pitfalls

What goes wrong at this step

  • No drift monitoring — sync runs, but you don't know if it's working
  • CDC schema changes break sync — when the source schema changes, the CDC pipeline often needs reconfiguration
  • Dual-write transactions — making both writes atomic is hard (2PC is rarely the answer)
  • Forgetting bulk operations — CDC handles row-by-row; bulk imports may not flow through
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