--- name: application-migration description: Guides comprehensive application migration projects including legacy system modernization, cloud migration, technology stack upgrades, database migration, and architecture transformation. Covers assessment, planning, migration strategies (strangler fig, big bang, phased), risk management, data migration, testing, and cutover. Use when migrating applications, modernizing legacy systems, moving to cloud, changing technology stacks, or when users mention "migration", "modernization", "replatform", "lift and shift", "refactor", "strangler pattern", or "legacy transformation". --- # Application Migration Plan and execute application migration projects—from legacy system modernization to cloud migration and technology stack transformation. ## Migration Workflow Follow this systematic approach for successful migrations: ## 1. Assess Current State Analyze the application portfolio and environment: ``` Actions: - Create application inventory (name, tech stack, dependencies) - Map data flows and integration points - Identify business criticality (critical/important/low) - Document compliance requirements (PCI-DSS, HIPAA, GDPR, etc.) - Measure current performance metrics (response time, throughput, uptime) ``` **Output:** Application assessment report with complexity scores (low/medium/high) **Example Assessment:** ``` Application: Customer Portal Tech Stack: Java 8, Oracle 11g, Apache Tomcat 7 Dependencies: Payment Gateway API, CRM System, Email Service Business Criticality: Critical (revenue-generating) Complexity: High (20+ integrations, legacy code) → Recommendation: Strangler fig pattern with 12-month timeline ``` ### 2. Select Migration Strategy Choose the approach based on complexity and business constraints: **Strangler Fig Pattern** (recommended for complex applications): - Build new functionality alongside old system - Incrementally redirect traffic to new components - Retire old components gradually - Timeline: 6-18 months - Risk: Low (gradual transition with rollback capability) **Big Bang Migration** (for simple applications): - Complete migration in single cutover event - All users switch simultaneously - Timeline: 1-3 months - Risk: High (no gradual rollback option) **Phased Migration** (for multi-tenant or regional deployments): - Migrate one tenant/region at a time - Validate each phase before proceeding - Timeline: 3-12 months - Risk: Medium (parallel operations required) ### 3. Plan Migration Create detailed execution roadmap with these components: **Timeline:** Define phases with 2-week sprint cycles **Resources:** Allocate developers (3-10), QA (2-4), DevOps (1-2), architects (1) **Budget:** Estimate 1.5-2x initial projection (migrations typically exceed estimates) **Risk Mitigation:** Document top 5 risks with contingency plans **Rollback Plan:** Test rollback procedures before cutover ### 4. Execute Migration Implement in controlled iterations: ``` Iteration Pattern: 1. Migrate component/module (1-2 weeks) 2. Deploy to staging environment 3. Run automated test suite (unit, integration, E2E) 4. Conduct performance testing (load, stress, spike) 5. Execute user acceptance testing (UAT) 6. Deploy to production with feature flag (OFF initially) 7. Monitor metrics for 48 hours 8. Enable feature flag for 10% of traffic 9. Gradually increase to 100% over 1 week 10. Retire old component after 30-day observation period ``` **Critical Rule:** Never migrate data and code simultaneously—migrate code first, then data. ### 5. Validate and Cutover Execute final switchover with validation: **Pre-Cutover Checklist:** - [ ] All automated tests passing (unit, integration, E2E) - [ ] Performance meets SLA requirements (response time < 2s for 95th percentile) - [ ] Data validation complete (row counts match, checksums verified) - [ ] Rollback procedure tested successfully - [ ] Monitoring dashboards operational - [ ] On-call team briefed and available - [ ] Communication sent to all stakeholders **Cutover Window:** Schedule during lowest traffic period (typically Sunday 2-6 AM) **Post-Cutover Monitoring:** Monitor these metrics for 72 hours: - Error rate (must be < 0.1%) - Response time (must be < 2s for 95th percentile) - Database connection pool utilization (must be < 80%) - CPU and memory usage (must be < 70%) - Business transaction success rate (must be > 99.5%) ## Reference Documentation Load detailed guides based on migration phase: - **[migration-assessment.md](references/migration-assessment.md)** - Comprehensive assessment framework with templates and tools. Load when starting assessment phase. - **[migration-strategies.md](references/migration-strategies.md)** - Detailed strategy patterns with decision matrices and application-specific recommendations. Load when selecting migration approach. - **[migration-planning.md](references/migration-planning.md)** - Resource planning, timeline estimation, governance setup. Load when creating migration roadmap. - **[execution-playbook.md](references/execution-playbook.md)** - Step-by-step implementation checklist with environment setup and deployment procedures. Load during execution phase. - **[best-practices.md](references/best-practices.md)** - Proven patterns, common pitfalls, and optimization techniques. Load when encountering challenges. - **[metrics-and-success-criteria.md](references/metrics-and-success-criteria.md)** - KPI definitions, measurement methods, success thresholds. Load when defining success criteria. - **[post-migration-activities.md](references/post-migration-activities.md)** - Decommissioning procedures, optimization strategies, monitoring setup. Load after cutover completion. ## Critical Success Factors **Never skip these steps:** 1. **Dependency mapping** - Unknown dependencies cause 60% of migration failures 2. **Data validation** - Verify data integrity before AND after migration (row counts, checksums, business rules) 3. **Performance testing** - Test with 2x expected peak load 4. **Rollback testing** - Execute full rollback procedure in staging before cutover 5. **Incremental deployment** - Use feature flags and canary releases (10% → 25% → 50% → 100%) **Budget Reality:** Migrations typically take 1.5-2x initial estimates. Plan accordingly. **Communication Cadence:** Send status updates to stakeholders weekly during planning, daily during execution. --- Source attribution: DauQuangThanh Original project: https://github.com/DauQuangThanh/hanoi-rainbow/blob/0e2ebaea024ad494bfd39cba73effa61a9c978cf/skills/application-migration/SKILL.md License: MIT License information: https://opensource.org/license/mit Original upstream instructions; downloaded from Mega AI Hub. ## Upstream license notice MIT License Copyright (c) 2025 Dau Quang Thanh Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions: The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software. THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE. # Mega AI Hub resource metadata Creator / publisher: DauQuangThanh Original project: https://github.com/DauQuangThanh/hanoi-rainbow/blob/0e2ebaea024ad494bfd39cba73effa61a9c978cf/skills/application-migration/SKILL.md Attribution basis: Recovered original package and original project license at a pinned revision Fields of work: Development & Engineering, Operations, Product Management, Project & Program Management Roles: Business Process Analyst, DevOps / SRE, IT Operations, Project Manager, Technical Product Manager Specialties: Backend, DevOps Tools: AWS, Azure, Docker, GCP, Kubernetes Country applicability: Country not specified Classification basis: Source catalog labels Instruction SHA-256: 80a3278f8cc12d25da3091deab2abe74dedf32d6eb7bcaec774e9ed034ef2153 Metadata reviewed: 2026-10-27 This metadata supersedes earlier Mega AI Hub catalog attribution. Original instruction and supporting files are preserved.