That legacy system has served you well for years—maybe decades. But now it's becoming a liability: the original developers are long gone, it runs on outdated technology, and every small change feels like defusing a bomb. You know migration is inevitable, but where do you start?
The Reality: Legacy migrations are among the highest-risk IT projects. But with proper planning, they don't have to be. The difference between success and disaster usually comes down to what happens before the first line of code is written.
This guide will walk you through the critical planning considerations that separate smooth migrations from the horror stories you've heard about.
Why Migrations Fail
Before diving into how to do it right, let's understand what goes wrong. Learning from others' mistakes is cheaper than making your own.
Underestimating Data Complexity
"It's just data—how hard can it be?" Famous last words. Legacy systems accumulate years of data anomalies, workarounds, and edge cases. Fields that were supposed to hold postcodes now contain notes. "Inactive" records turn out to be critical for historical reporting. Duplicate records have subtle differences that actually matter.
Losing Institutional Knowledge
The old system does things that aren't documented anywhere—they exist only in the heads of long-serving staff. "Oh, we always do it that way because of the Henderson account back in 2008." That tribal knowledge is easy to lose and expensive to rediscover.
The Big-Bang Approach
Flipping the switch on a Friday night and hoping everything works Monday morning. When it doesn't (and something always doesn't), you're left scrambling with no fallback while the business grinds to a halt.
Ignoring the Human Factor
Technically perfect migrations still fail if people don't adopt the new system. Change resistance, inadequate training, and poor communication can doom even the best-built replacement.
Discovery Phase Essentials
The discovery phase is where you uncover what the legacy system actually does—not what the documentation says, not what management thinks, but what really happens day-to-day.
Key Discovery Activities
Process Shadowing
Watch actual users do their actual jobs. Don't just ask "what do you do?"—observe them doing it. You'll discover workarounds, shortcuts, and undocumented processes that are invisible in any other way.
Data Archaeology
Profile your data thoroughly. What's actually in those fields? What are the real relationships between records? Where are the inconsistencies? This isn't a quick task—budget proper time for it.
Integration Mapping
Document every system that touches the legacy system—including that spreadsheet someone emails every morning and the report that feeds into another department's process. These hidden integrations are migration landmines.
Exception Cataloguing
Every business has exceptions—special customers, unusual processes, edge cases. The legacy system handles them somehow. Find out how, because the new system will need to handle them too.
Critical question to ask users: "What would make your job impossible if the new system didn't do it?" This cuts through wish-lists to reveal true requirements.
How AI Is Transforming Legacy Discovery and Analysis
One of the most time-consuming aspects of legacy migration has always been understanding what the old system actually does. AI-assisted development tools are changing this dramatically.
Automated Code Analysis
AI can rapidly analyse legacy codebases—even poorly documented ones—to identify business logic, data flows, and hidden dependencies. What once took weeks of manual code review can now be accomplished in days.
Documentation Generation
AI tools can generate documentation from legacy code, creating readable explanations of complex business rules that may never have been properly documented—or whose documentation is decades out of date.
Pattern Recognition
AI excels at identifying patterns across large codebases—finding where similar logic is duplicated, spotting inconsistencies, and mapping the true relationships between system components.
Risk Assessment
By analysing code complexity, coupling, and usage patterns, AI can help identify the highest-risk areas of a migration—allowing teams to focus testing and validation efforts where they matter most.
This means faster, more thorough discovery phases, fewer surprises during migration, and ultimately lower project risk. The institutional knowledge trapped in legacy code becomes accessible in ways that weren't possible before.
Data Migration Planning
Data migration is often the most underestimated part of any legacy project. It's not just moving data from A to B—it's cleaning, transforming, and validating while maintaining business continuity.
Data Cleaning
Migration is your chance to clean house—but be strategic about it.
- Identify and merge duplicate records
- Standardise formats (dates, addresses, names)
- Archive genuinely obsolete data
- Verify before deleting anything
Data Mapping
Define exactly how old data translates to new structures.
- Field-by-field mapping documentation
- Transformation rules for format changes
- Default values for new required fields
- Handling of orphaned records
Data Validation
How will you know the migration worked correctly?
- Record count reconciliation
- Financial totals verification
- Sample record spot-checks
- Business user validation sessions
The Migration Rehearsal
Never migrate production data without practice runs. Perform full migration rehearsals with realistic data volumes. Time them. Find the problems. Fix them. Repeat until you're confident. Most organisations need 3-5 rehearsals before the real thing goes smoothly.
Parallel Running vs Cutover Strategies
How do you actually make the switch? There are several approaches, each with trade-offs.
Parallel Running
Both systems operate simultaneously. Users enter data into both (or data is synchronised), and results are compared to verify the new system works correctly.
Advantages:
- • Lowest risk—fallback always available
- • Issues found in real conditions
- • Builds user confidence gradually
Disadvantages:
- • Double workload during parallel period
- • Extended timeline and cost
- • Can delay commitment to new system
Phased Cutover
Migrate in stages—by department, by function, by customer segment, or by geography. Each phase is a smaller, more manageable migration.
Advantages:
- • Learn from early phases
- • Contains blast radius of problems
- • Spreads change management load
Disadvantages:
- • Requires careful phase planning
- • May need temporary integrations
- • Extended total project duration
Big-Bang Cutover
Complete switch at a single point in time. The old system is turned off; the new one takes over entirely.
Advantages:
- • Clean break—no prolonged transition
- • Lower total project cost
- • Simpler for tightly integrated systems
Disadvantages:
- • Highest risk—all eggs in one basket
- • Problems affect everyone at once
- • Requires extensive pre-testing
Our Recommendation
For most businesses, we recommend a phased approach with parallel running within each phase. This balances risk mitigation with practical timelines. The specific strategy depends on your system complexity, risk tolerance, and operational constraints.
Managing Stakeholder Expectations and Change Resistance
Technical success means nothing if people won't use the new system. Change management is not optional—it's essential.
Communicate Early and Often
Don't surprise people. Explain why the migration is happening, what it means for them, and how they'll be supported. Silence breeds anxiety and resistance.
Involve Users in Design
People support what they help create. Include representative users in requirements gathering, design reviews, and testing. They become advocates rather than resistors.
Acknowledge the Loss
People have invested years learning the old system. They're experts in it. Recognise that starting over feels like a demotion. Validate their expertise and show how it translates.
Identify and Empower Champions
Find enthusiastic early adopters in each team. Train them first. Let them support their colleagues. Peer influence is more powerful than top-down mandates.
Plan for the Productivity Dip
Even with perfect training, productivity will drop temporarily as people learn the new system. Plan for this—adjust deadlines, add temporary support, set realistic expectations with management.
Warning sign: If stakeholders are saying "just tell us when it's done," you have a change management problem brewing. Engagement is essential, even when people seem too busy.
Choosing the Right Partner
Legacy migrations require deep expertise. Here's what to look for in a migration partner:
Green Flags
- Asks lots of questions about your business, not just the technology
- Emphasises discovery phase and realistic planning
- Can speak to both technical and business stakeholders
- Has specific experience with similar migrations
- Discusses risk mitigation and rollback strategies upfront
- Includes change management in their approach
Red Flags
- Gives a fixed quote without thorough discovery
- Promises everything will be "easy" or "quick"
- Focuses only on the new system, not the migration process
- Dismisses concerns about data complexity
- No clear methodology for testing and validation
- Wants to start coding immediately
Your Pre-Migration Checklist
Before you begin any migration project, ensure you can answer these questions:
- âś“Do we fully understand what the legacy system does (not just what we think it does)?
- âś“Have we documented all integrations, including informal ones?
- âś“Do we have a realistic data migration and validation plan?
- âś“Have we planned our cutover strategy with appropriate risk mitigation?
- âś“Is there a rollback plan if things go wrong?
- âś“Do we have stakeholder buy-in and a change management plan?
- âś“Have we allocated realistic time and budget, including contingency?
- âś“Do we have the right partner with proven migration experience?
Planning a Migration?
We've guided Adelaide businesses through complex legacy migrations—from decades-old systems to modern platforms. Let's discuss your situation and help you plan a successful transition.
Start the ConversationAt Expeed Technology, we believe successful migrations start with thorough planning. We won't rush you into development—we'll help you understand exactly what you're dealing with first. That's how we ensure your migration succeeds where others fail.