Hiring for Technology Migration: The Complete Guide

Common Technology Migration Scenarios

Frontend Framework Migrations

Examples:

• AngularJS → Angular 2+
• AngularJS → React
• jQuery → React/Vue
• Backbone.js → Modern framework
• Legacy CSS → CSS-in-JS or Tailwind

Team Needs:

• Expertise in both old and new framework
• Migration tooling (codemods, automated refactoring)
• Understanding of component architecture
• Testing strategies for migration

Challenges:

• Maintaining feature parity
• Gradual migration path
• Team retraining
• Performance differences

Backend Language/Framework Migrations

Examples:

• Python 2 → Python 3
• Java 8 → Java 17+
• .NET Framework → .NET Core
• Ruby on Rails version upgrades
• PHP 5 → PHP 8

Team Needs:

• Deep knowledge of both versions
• Understanding of breaking changes
• Migration tooling and scripts
• Testing and validation

Challenges:

• Breaking changes
• Dependency updates
• Performance regressions
• Team adaptation

Infrastructure Migrations

Examples:

• On-premise → Cloud (AWS, GCP, Azure)
• VM-based → Container-based (Docker, Kubernetes)
• Monolithic deployment → Microservices
• Data center → Cloud

Team Needs:

• Cloud platform expertise
• Infrastructure as code
• DevOps/CI/CD experience
• Migration tooling

Challenges:

• Data migration
• Network and security
• Cost optimization
• Zero-downtime migration

Database Migrations

Examples:

• MySQL → PostgreSQL
• Oracle → PostgreSQL
• MongoDB → DocumentDB
• SQL Server → Azure SQL

Team Needs:

• Database expertise
• Migration tooling
• Data integrity knowledge
• Performance optimization

Challenges:

• Data migration without downtime
• Query compatibility
• Performance tuning
• Backup and recovery

Team Composition for Technology Migrations

Core Team Structure

1. Migration Lead (1)

• Plans migration strategy
• Coordinates migration execution
• Makes technology decisions
• Manages timeline and risks

Skills Needed:

• Migration project experience
• Strong in both old and new tech
• Project management
• Communication

2. Senior Engineers - New Tech (2-3)

• Experts in target technology
• Build new implementation
• Set standards and patterns
• Mentor team on new tech

Skills Needed:

• Deep expertise in new technology
• Can teach and mentor
• Strong coding skills
• Best practices knowledge

3. Senior Engineers - Old Tech (1-2)

• Understand legacy system deeply
• Can explain old patterns
• Help with migration planning
• Support during transition

Skills Needed:

• Expertise in old technology
• Can read and explain legacy code
• Patience with old systems
• Communication skills

4. Migration Engineers (2-4)

• Execute migration day-to-day
• Work with both old and new
• Write migration scripts/tooling
• Test and validate

Skills Needed:

• Both old and new tech knowledge
• Migration tooling experience
• Attention to detail
• Testing skills

Optional Roles

QA/Testing:

• Test migration thoroughly
• Ensure feature parity
• Regression testing
• Performance validation

DevOps/SRE:

• Infrastructure for new tech
• Deployment pipelines
• Migration tooling
• Monitoring

Migration Strategies

Strategy 1: Big Bang (Rarely Recommended)

Approach: Migrate everything at once

Pros:

• Clean break
• No dual-system complexity
• Faster (if it works)

Cons:

• High risk
• No rollback plan
• All-or-nothing
• Stressful

When to Use:

• Small, isolated systems
• Low business impact
• Can't run both systems
• Team is very confident

Strategy 2: Strangler Fig (Recommended)

Approach: Gradually replace parts

Pros:

• Low risk
• Incremental progress
• Can rollback pieces
• Learn as you go

Cons:

• Longer timeline
• More complex (two systems)
• Requires coordination

How It Works:

1. Identify migration units (components, modules, services)
2. Build new version of one unit
3. Route traffic gradually (10% → 50% → 100%)
4. Decommission old version
5. Repeat for next unit

Strategy 3: Parallel Run

Approach: Run both versions, compare outputs

Pros:

• Validates correctness
• Low risk
• Can compare performance
• Gradual cutover

Cons:

• Expensive (run both)
• Complex data sync
• Longer timeline

When to Use:

• Critical systems
• Need high confidence
• Can afford dual operation

Strategy 4: Feature Flag Migration

Approach: Use feature flags to toggle between old and new

Pros:

• Easy rollback
• Gradual rollout
• A/B testing possible
• Low risk

Cons:

• Requires feature flag infrastructure
• More code complexity
• Need to maintain both paths

When to Use:

• Have feature flag system
• Want gradual rollout
• Need easy rollback

Hiring Strategy

Key Skills to Look For

1. Migration Experience

• Has done technology migrations before
• Understands migration challenges
• Knows common pitfalls
• Can estimate effort

2. Dual Technology Expertise

• Strong in old technology
• Strong in new technology
• Can bridge the gap
• Understands differences

3. Migration Tooling

• Experience with codemods
• Automated refactoring tools
• Migration scripts
• Testing migration tools

4. Incremental Thinking

• Prefers gradual migration
• Understands strangler fig pattern
• Can plan incremental steps
• Risk-aware

5. Communication

• Explains migration approach
• Documents decisions
• Coordinates with team
• Manages expectations

Red Flags

❌ Only new tech experience - May not understand migration challenges
❌ Wants big bang migration - Doesn't understand incremental approach
❌ No migration experience - May underestimate complexity
❌ Can't work with old code - Will struggle with legacy
❌ Unrealistic timelines - Doesn't understand migration time

Where to Find Candidates

1. Companies That Have Migrated

• Look for engineers who worked on migrations
• They understand the challenges
• Have real experience

2. Open Source Contributors

• Many contribute to migration tools
• Understand migration patterns
• Often available for consulting/hiring

3. Framework Communities

• Engineers active in framework communities
• Often help others migrate
• Understand both old and new

4. Internal Team

• Current engineers know the system
• Can learn new tech
• Understand business context

Migration Tooling and Automation

Types of Migration Tooling

1. Codemods

• Automated code transformations
• Framework-specific (e.g., react-codemod)
• Can handle 60-80% of migration
• Requires manual review

2. AST Transformers

• Parse and transform code
• More powerful than codemods
• Custom transformations
• Requires expertise

3. Migration Scripts

• Custom scripts for data/configuration
• Database migrations
• Infrastructure changes
• Deployment automation

4. Testing Tools

• Automated comparison testing
• Feature parity validation
• Performance benchmarking
• Regression testing

Building vs. Buying Tooling

Buy/Use Existing:

• Framework migrations often have tools
• Open source migration tools
• Lower cost, proven

Build Custom:

• Unique migration needs
• No existing tools
• Higher cost, tailored

Recommendation: Use existing tools when possible, build custom only when needed.

Budget Planning

Cost Components

1. Engineering Salaries

• Migration Lead: $160-220K
• Senior Engineers (new tech): $150-200K each
• Senior Engineers (old tech): $140-180K each
• Migration Engineers: $120-160K each
• Total: $600K-1.2M annually

2. Migration Tooling

• Existing tools: $0-20K (licenses if needed)
• Custom tooling: $50K-150K (development)
• Testing tools: $10K-50K

3. Infrastructure

• Running both systems: $20K-100K/year
• New infrastructure: $30K-150K/year

4. Timeline

• Small migrations: 3-6 months
• Medium migrations: 6-12 months
• Large migrations: 12-18 months

Cost Optimization

• Incremental migration - Spread cost over time
• Reuse existing infrastructure - Where possible
• Internal team - Lower cost, know the system
• Open source tooling - Use existing tools

Common Pitfalls

1. Underestimating Migration Complexity

Problem: Migrations are more complex than they appear.

Solution:

• Start with small pilot
• Add 20-30% buffer to estimates
• Plan for unknowns
• Use incremental approach

2. Feature Parity Assumptions

Problem: Assuming new version has exact same features.

Solution:

• Audit what old version actually does
• Test feature parity thoroughly
• Document differences
• Plan for feature gaps

3. Team Retraining Gaps

Problem: Team doesn't know new technology well.

Solution:

• Training before migration starts
• Pair programming with experts
• Code reviews and mentoring
• Gradual learning curve

4. Performance Regressions

Problem: New technology performs worse than old.

Solution:

• Performance testing before migration
• Benchmark both versions
• Optimize new version
• Have rollback plan

5. Dependency Hell

Problem: Updating dependencies breaks things.

Solution:

• Update dependencies incrementally
• Test thoroughly after each update
• Understand breaking changes
• Have rollback plan

6. Timeline Pressure

Problem: Unrealistic deadlines lead to shortcuts.

Solution:

• Set realistic expectations
• Incremental approach reduces risk
• Better to do it right than fast
• Regular progress updates

Recruiter's Cheat Sheet

Key Interview Questions

"Tell me about a technology migration you've done. What was your approach?"

• Look for: Incremental approach, migration experience, specific examples
• Red flags: Big bang approach, no experience, vague answers

"How would you migrate [specific old tech] to [specific new tech]?"

• Look for: Migration strategy, tooling knowledge, risk awareness
• Red flags: No strategy, unrealistic timeline, underestimates complexity

"How do you ensure nothing breaks during migration?"

• Look for: Testing strategy, gradual rollout, rollback plan
• Red flags: No testing plan, no rollback, assumes perfection

Salary Expectations

Migration Expertise Premium:

• 10-20% above standard senior engineer rates
• Migration experience is valuable
• Dual tech knowledge commands premium

Typical Ranges (US, 2026):

• Migration Lead: $160-220K
• Senior Engineer (migration): $140-200K
• Migration Engineer: $120-160K

Timeline Reality

Factors Affecting Timeline:

• System size and complexity
• Team size and experience
• Migration strategy (incremental vs. big bang)
• Breaking changes in new tech
• Testing and validation requirements

Success Factors

1. Strong Migration Leadership

• Clear migration strategy
• Makes good technology decisions
• Manages timeline and risks
• Communicates effectively

2. Incremental Approach

• Strangler fig or feature flags
• Low risk, learn as you go
• Can adjust based on learnings
• Maintains business continuity

3. Team Composition

• Mix of old and new tech expertise
• Migration experience
• Strong communication
• Attention to detail

4. Migration Tooling

• Automated where possible
• Reduces manual work
• Consistent transformations
• Testing and validation

5. Testing and Validation

• Comprehensive testing strategy
• Feature parity validation
• Performance testing
• Rollback procedures

Timeline: Typical Technology Migration

Months 1-2: Planning and Setup

• Understand current system
• Choose migration strategy
• Set up migration tooling
• Train team on new tech

Months 3-6: Pilot Migration

• Migrate small, low-risk component
• Validate approach
• Learn and adjust
• Build confidence

Months 7-12: Incremental Migration

• Migrate components incrementally
• Route traffic gradually
• Decommission old versions
• Monitor and optimize

Months 13-18: Completion

• Migrate remaining components
• Remove old technology
• Performance optimization
• Documentation and handoff