What is Legacy Migration, and How does it Work?

Legacy migration is a difficult decision for an organization running mission-critical software. These systems, created decades ago, often power finance, healthcare, manufacturing and other platforms. But they also grow slowly, and the maintenance costs rise year by year. 

This guide is for leaders who have legacy applications and understand that doing nothing is no longer an option. In this article, you will learn about legacy migration, its challenges, when it becomes necessary, and how to approach it. 

We are aiming to reduce risks and help you plan a safe modernization journey. 

What Is a Legacy Application?

A legacy application is software that has been in use for a long time. And the company continues using it even though it may be old. It can have outdated technology, design, or functionality. These applications often have dependencies on older systems, hardware or software components. And they may be difficult or costly to update or replace.

Legacy applications can pose several challenges. They may lack documentation. They may rely on third-party components no longer supported. Or they need specialized skills that are hard to find today. One of the biggest concerns is security. Older systems are more vulnerable to breaches without regular vendor patches. Integrating them with modern platforms or APIs can also be slow and costly, if not impossible. 

Despite these challenges, many businesses cannot abandon legacy systems. Because they hold years of business logic that is critical for daily operations.

For example, a COBOL-based application in a bank. It still runs core transactions but resist integration with mobile banking features. Or an aging ERP system that is used in manufacturing. It can support production scheduling, but every update requires manual fixes. In both cases, the system is too valuable to discard. And it is too outdated to sustain without modernization. 

Why Businesses Still Have Outdated Legacy Applications

Businesses often still have outdated legacy applications for several reasons:

• Cost. For many organizations, the cost of legacy application migration outweighs the benefits.
• Risk. Legacy applications often play a critical role in business operations. Legacy software modernization carries risks, such as the potential for disruptions, data loss. 
• Complexity. Legacy applications are integrated into a day-to-day workflow. They usually connect to dozens of other applications. But concurrently, they lack proper documentation and old knowledge. That further complicates undoing of dependencies without causing damage to something significant. 
• Regulatory Compliance. In Financial, Healthcare, and Government industries, recertification of a system that is migrated can take months and incur additional expense.
• Vendor Lock-in. A few older programs can be locked into certain vendors that don’t exist anymore.
• Cultural Resistances to Change. The employees get comfortable with one specific legacy application. And possibly they will resist a move to a new system.
• Skill Shortage. Not many developers now understand how to deal with Delphi or old .NET platforms. So maintenance of existing systems becomes more difficult, but upgrading or replacing them is even more risky without professional assistance.

When We Need Legacy System Migration

For seamless scaling and growth, it’s important to assess whether your legacy system needs to be migrated. Legacy system migration becomes necessary under the following circumstances:

• Obsolete Technology: When the technology stack used in the legacy system becomes outdated and unsupported, it poses a risk to the organization’s operations due to potential security vulnerabilities, lack of vendor support, and compatibility issues with modern systems.
• Inefficient Performance: Legacy systems may suffer from performance issues, such as slow response times, limited scalability, and frequent downtime. Legacy system migration to modern infrastructure and technologies can improve system performance and reliability.
• Business Growth and Change: As businesses evolve and grow, legacy systems may struggle to meet new requirements, support increased user loads, or integrate with other systems. Legacy system migration to modern platforms can enable scalability, agility, and support for new business processes.
• Compliance and Regulation: Changes in regulatory requirements or industry standards may necessitate updates to legacy systems to ensure compliance. Legacy system migration can involve implementing new features or functionalities to meet regulatory demands.
• High Maintenance Costs: Legacy systems often require substantial investment in maintenance and support, including patching, bug fixes, and troubleshooting. Legacy system migration to newer systems may reduce ongoing maintenance costs and improve the return on investment.
• Limited Integration and Innovation: Legacy systems may lack the flexibility and interoperability required to integrate with newer technologies and services, hindering innovation and business growth. Legacy system migration enables organizations to leverage modern integration frameworks and APIs to connect with third-party services and platforms.
• User Experience Improvement: Legacy systems may offer outdated user interfaces and workflows that result in a poor user experience. Legacy application migration to modern platforms allows the adoption of user-friendly interfaces and intuitive design principles, enhancing usability and productivity.
• Strategic Objectives: Organizations may initiate legacy software modernization as part of their strategic initiatives to align IT infrastructure with long-term business goals, improve competitiveness, and future-proof technology investments.

Overall, the legacy system migration process is typically undertaken to address issues related to technological obsolescence, inefficiency, compliance, scalability, and strategic alignment with business objectives. It involves careful planning, resource allocation, and risk management to ensure a successful transition to modern platforms while minimizing disruption to ongoing operations.

What is a Legacy Migration and How to Do It?

Legacy system migration is a complex process that requires careful planning to ensure a smooth transition and minimize risk and business disruption.

The first part of any legacy system migration strategy should be to conduct a thorough audit, identifying problem areas of the system. Next, define the business goals and objectives driving the migration, such as improving performance, scalability or compliance. Assess the scope of the migration and develop a detailed migration plan with timelines, milestones, resource allocation and risk management strategies.

Migrate vs. Modernize vs. Hybrid: A Decision Matrix

When dealing with outdated systems, one of the first questions is which path to take. There are three common strategies:

• Migration – moving applications to a newer platform with minimal code changes.
• Modernization – aligning the system with today’s frameworks and standards.
• Hybrid – this approach combines both. You migrate critical functions quickly, but modernize components gradually. 

Deciding between the right and wrong path is based on your case. Consider your future and available resources. Migration project will make more sense to you if speed and disruption are vital.  If your focus is on scalability and future innovation, modernization is the better route. More and more companies are also choosing a hybrid approach – it keeps downtime low and lets you modernize step by step. 

To make things easier, we have put together a simple decision matrix to guide the choice.

Criteria	Migrate	Modernize	Hybrid
Business goals	Keep system stable; extend lifespan	Transform IT to enable new features and agility	Balance continuity with gradual innovation
Downtime tolerance	Minimal downtime required	Some planned downtime is acceptable	Limited downtime with phased rollout
Compliance needs	Maintain existing certifications	Re-certification is required but enables future compliance	Preserve compliance while modernizing in stages
Budget	Lower upfront cost, higher long-term maintenance	Higher upfront investment, lower long-term costs	Moderate cost spread over time
Team skills	Existing legacy expertise is sufficient	Requires modern tech expertise (cloud, APIs, new frameworks)	Mixed skills: legacy knowledge plus modern stack skills

Legacy Modernization & Migration Strategies: The 7 Rs

When planning a legacy system update, organizations typically choose from the 7 Rs. They outline common migration and modernization strategies. Each has different trade-offs.

• Rehost – moving the application to a new infrastructure without code changes. It is fast, with low disruption. But it keeps technical debt. This strategy best fits when speed is critical and downtime tolerance is low.
• Replatform – making minor optimizations while moving to a new runtime or database. It improves performance but is also still tied to legacy code. This is good for apps that need cloud scalability but not a full rewrite. 
• Refactor – optimizing and cleaning up the existing codebase without altering the architecture. This improves maintainability but limits impact on scalability or innovation. Such an approach is the best fit when legacy code is valuable but messy.
• Rearchitect – redesigning application structure. For example, moving from monolithic architecture to microservices. It enables integration and agility but this approach is complex. If you have long-term digital transformation goals, this is your best fit.
• Rebuild/replace – rewriting from scratch or adopting a new product. If you opt for this approach, you future-proof your platform. But rebuilding can be costly and lengthy. 
• Retire – decommissioning outdated systems that no longer add value. This way, you will reduce cost and complexity. But ensure that there are no critical dependencies. This approach is the best fit for redundant apps or modules. 
• Retain/Encapsulate – keeping the system but wrapping it with APIs to extend lifespan. This buys time for gradual migration but legacy issues might persist underneath. Choose this approach when the budget is tight or replacement is not yet viable. 

Industries running in mainframes or IBM i (AS/400) often rely on a phased or hybrid approach. They prioritize safety and regulatory compliance. At the same time, they modernize high-value components first.

Integration-Layer Alternatives: ESB vs. iPaaS vs. API Gateway 

Migrating legacy systems can be a suitable option for many projects. But sometimes the smartest move is to decouple it through an integration layer. Middleware preserves stability and exposes the new system to modern apps and services. This approach is common when budgets are tight and skills are scarce.

There are three main alternatives:

• Enterprise Service Bus (ESB) – a centralized unit for connecting multiple applications. It is mature and reliable but slower to adapt. Suitable for large enterprises with established SOA. 
• iPaaS (Integration Platform as a Service) – cloud-based integration with prebuilt connectors and monitoring. With this approach, you can build fast, but subscription costs can be high. If you are embracing SaaS and hybrid cloud, this solution might be for you.
• API gateway – a lightweight layer that exposes legacy functions as APIs. It is simple and supports microservices. But you will have limited orchestration. If you don’t need a full ESB, this alternative is the best fit.

All three options provide monitoring, logging and retry mechanisms. They help reduce downtime when legacy systems struggle under load. The trade-off is governance. ESBs enforce strict control but slow agility. API gateways favor speed with less central oversight. And iPaaS sits in between: it offers governance features with cloud-native flexibility.

Using an integration layer doesn’t eliminate technical debt, but it buys time. It allows organizations to innovate at the edges and plan a safer migration for the core.

Legacy System Migration Process Step-by-Step

Legacy data migration is a critical aspect of migrating legacy systems to modern platforms. Consider these legacy platform upgrade steps:

1. Determine the scope of the data migration, including which data sets, tables, or databases will be migrated. 
2. Determine the goals of the data migration, such as preserving data integrity, minimizing downtime, and optimizing data quality.
3. Conduct a thorough assessment of the existing data environment, including data structures, schemas, formats, and storage systems.
4. Document data dependencies, relationships, and metadata to understand how data is used in the legacy system.
5. Identify any data anomalies, duplicates or inconsistencies that may need to be addressed during the legacy system migration process.
6. Plan a legacy system migration strategy.
7. Develop a data legacy system migration strategy that describes the approach, tools, and methods that will be used to migrate the data.
8. Create a data mapping document that defines how data elements in the legacy system relate to data elements in the target system.
9. Extract data from the legacy system using appropriate extraction methods and tools.
10. Check the extracted data for accuracy and completeness before proceeding to the next step.

Step 1. Creating a Legacy System Migration Strategy

To successfully migrate your application, you need to choose the right strategy. Organizations differ in business, processes, and functionality. Therefore, there cannot be one solution for all. The right choice will depend on the needs of the application, available funding and team, and overall business goals. This phase may require detailed planning as it may involve several sub-projects.

But before deciding how to move code, you should consider what data to transfer and how to validate it. Also, define migration goals. Are you focusing on a complete transfer or only active records? 

After you set all the extraction and transformation rules, establish reconciliation ratios. It is necessary to verify accuracy. A common benchmark is 100% reconciliation for critical data and 95-98% for less critical data. 

Use sampling methods to speed up validation. For large datasets, reconcile 5-10% random samples. Include sampling of high-risk data and define how to report reconciliation results.

Step 2. Making a Backup

Before initiating any legacy system migration process, it’s crucial to make a comprehensive backup of all relevant data and configurations from your existing legacy systems. This ensures that you have a failsafe mechanism to restore operations in case of any unforeseen issues or data loss during the migration process. 

By making a comprehensive backup of your legacy systems before initiating the migration process, you can mitigate the risk of data loss and ensure that you have a reliable mechanism to restore operations in case of any unforeseen issues during the migration.

Step 3: Preparing the Target Environment

Preparing the target environment is a critical step in the legacy code migration process, ensuring that the new systems or infrastructure are ready to receive the migrated data and applications. By effectively preparing the target environment, you can ensure a smooth and successful migration process, minimizing risks and maximizing the benefits of the new systems or infrastructure.

Step 4. Testing the Legacy Migration

Testing is critical for the legacy code migration process. It ensures the migrated systems and data are functioning properly. It should cover three layers:

Security risks and compliance testing – addresses vulnerabilities, access controls and high data protection measures. Include penetration tests, encryption checks and role-based access reviews. For regulated industries, prepare audit-ready evidence such as reconciliation reports. Also, change logs and compliance certifications.

Functional testing – ensures that business processes and integrations behave as expected. Regression tests help confirm that nothing critical broke during migration.

Non-functional testing – validates performance and reliability. Define clear SLAs. For example, p95 response times under 200 ms for key transactions and 99.9% uptime targets. Load and stress testing should reveal if the new environment scales under peak demand.

By adhering to a systematic approach to testing, you can confirm the success of the migration and ensure that the migrated systems meet the required standards of quality, performance and reliability before they go into production.

Step 5. Migrating

After completing all the necessary preparations, you can start migrating your legacy applications. Migrating your legacy systems to the new environment involves executing the actual transfer of data, applications, and configurations from the old systems to the target environment. A phased migration of software applications helps you test code efficiently and resolve any issues that may arise at small levels.

Step 6. Monitoring the System after the Migration

After completing the migration of your legacy systems to the new environment, it’s crucial to monitor the performance, stability, and security of the system to ensure business continuity. 

Define service level objectives (SLOs) aligned with business KPIs. Typical metrics include:

• Incident rate – track defects per month and compare to pre-migration baselines.
• MTTR (Mean Time to Recovery) – measure how quickly teams can resolve incidents. A post-migration target is often under one hour for priority issues.
• Performance SLOs – monitor response times, error rates and throughput against defined thresholds.
• Cost controls – compare cloud services spend and baseline infrastructure costs. It is needed to ensure migration delivers ROI rather than budget overruns.

By monitoring the system post-migration, you can proactively identify and address any issues or performance concerns, ensuring that the migrated systems continue to operate effectively and meet the needs of your organization.

Risk Register (Template) & Mitigation Playbook

Every migration should maintain a risk register with clear ownership, mitigation steps and expected residual risk. There is a table below based on common challenges:

Risk	Owner	Mitigation	Residual
Data integrity loss	Data architect	Reconciliation plan (row counts, p95 checksums, exception reports)	Low
Extended downtime	Ops lead	Phased cutover, rollback plan, off-peak scheduling	Medium
Licensing overlap	Procurement	Track old/new licenses, negotiate co-term, retire unused assets	Low
Hardware compatibility	Infrastructure	Sandbox test with vendor-certified hardware	Medium
Ecosystem complexity	Solution architect	Map dependencies, decouple via APIs, use middleware (ESB/iPaaS)	Medium
Skills scarcity (Delphi)	PM / HR lead	Hire niche contractors, cross-train internal staff	High
Compliance gaps	Security officer	Audit trail, encryption, role-based access, pre-certification reviews	Low

Keeping the register active ensures that risks are visible and addressed continuously. 

Security and Compliance Checklist

Legacy app migration might expose sensitive data. It also requires alignment with regulatory standards. We have prepared a checklist to help reduce risk and ensure audit readiness:

• Data classification. Find confidential or business-critical data before migration.
• Access model. Enforce least-privilege roles, MFA and segregation of duties in the target environment.
• Logging & audit trails. Enable system-wide logging with immutable storage. Ensure logs capture user actions and administrative changes.
• Encryption. Encrypt data in transit and at rest to ensure high data protection measures.
• Compliance sign-offs. Validate controls against industry standards (HIPAA, PCI DSS, GDPR, SOX). Secure regulator or auditor approval before go-live.

This checklist safeguards the migration process and long-term trust in the modernized system.

Change Management and Training Plan

Technology migration succeeds only if people adopt it. A change management and training plan helps minimize resistance and speed up adoption:

• Stakeholder map. Identify executives, business owners and end users. Assign champions to support adoption.
• Communication. Share clear updates before, during and after migration.
• Training assets. Provide guides and tutorials so users can practice safely.
• Adoption metrics. Track support tickets to measure progress. Set target metrics in advance.

Effective communication and training ensure the migration is embraced and not resisted.

Budgeting and ROI: Estimating the Business Case

A strong migration case starts with understanding the total cost of ownership (TCO). Key drivers include: licensing, hardware refresh cycles, vendor support, maintenance hours and compliance costs. 

Legacy systems often consume a disproportionate share of IT budgets. A simple payback model looks at maintenance savings (cutting support hours by 30-40%) and risk reduction (avoiding fines, breaches or contract losses tied to outages). Many organizations see ROI within 18–36 months. This is especially common when migrations provide infrastructure cost savings and enable cloud elasticity. 

Case Study: ERP Legacy Code Migration 

A European print-industry software vendor turned to Softacom to modernize its ERP. We added localization (multi-currency, 100+ unit types), integrated cloud storage, and optimized webmail. The results: 97% smaller payloads, 90% faster load times, and a platform ready for global expansion with improved UX and scalability.

Conclusion

For legacy migration, you need a practical migration plan. The right strategy depends on your goals and resources. It can help you control costs and achieve measurable ROI.

Ready to explore your options? Book a call with Softacom.