What is legacy system migration and why should a company migrate a legacy system?

It’s often essential for companies looking to reduce operational risk, increase system reliability, and stay competitive in a fast-evolving digital landscape.

Legacy systems typically rely on unsupported technologies, are expensive to maintain, and struggle to integrate with modern tools. Migrating to a newer stack helps enhance performance, lower long-term costs, meet security and compliance standards, and enable new digital capabilities that improve customer and employee experiences.

What are the main types of legacy system migration?

There are several migration and, at the same time, modernisation approaches, each varying in complexity, cost, and business impact. Here is a quick overview:

• Rehosting (lift and shift) – moving the system to a new infrastructure with minimal changes.
• Replatforming – making slight optimisations while shifting to a new platform.
• Refactoring – restructuring and optimising old system without altering core functionality.
• Rearchitecting – redesigning the system architecture for improved scalability and performance.
• Rebuilding – rewriting the entire system from scratch to meet current and future requirements.

Choosing the right method depends on your system’s complexity, goals, and available resources. For a deeper dive, see our detailed guide.

How to plan a successful legacy system migration strategy?

Planning a successful strategy for legacy system migration requires a structured, step-by-step approach to ensure minimal disruption to business operations and the secure handling of sensitive data.

Here’s how to approach the legacy system migration process effectively:

Assess the existing legacy system

Begin with a thorough audit of your outdated systems, identifying dependencies, performance bottlenecks, and areas of technical debt. This evaluation forms the foundation for understanding the scope and risks of the migration.

Define clear objectives of a migration process

Establish specific, measurable goals for the migration, such as improving performance, enhancing security, reducing costs, or enabling integration with modern platforms. These objectives will guide decision-making throughout the migration process.

Choose the right strategy for your legacy system migration process

Select the most appropriate migration approach (e.g., rehosting, replatforming, or refactoring) based on your system’s complexity, available resources, and long-term IT vision. This decision directly impacts the success of both the data migration and the overall transition to the new system.

Build a detailed migration plan

Develop a roadmap that includes timelines, resources, responsibilities, risk mitigation strategies, and fallback procedures. A solid plan ensures continuity of business operations and prevents surprises during execution.

Focus on legacy migration and testing

Prioritise the secure, accurate transfer of sensitive data to the new system, followed by rigorous testing to validate functionality, performance, and user experience. This phase is critical to avoiding costly errors and downtime.

Provide post-migration support and optimisation

After the go-live, monitor the new system closely to resolve any issues, fine-tune performance, and provide training or documentation as needed. Continuous improvement ensures that the migrated system delivers lasting value.

A well-executed migration process not only modernises technology but also strengthens the foundation for future innovation and growth. Careful planning and sticking to it throughout the process is of paramount importance.

What are the benefits of migrating legacy systems?

Migrating from outdated legacy systems to modern technology offers a range of strategic and operational benefits.

Key advantages to take into consideration include:

Improved performance

Modern systems are optimised for speed and efficiency, allowing for faster processing and better resource utilisation compared to aging hardware infrastructure, leading to smoother operations and better user experiences.

Reduced costs

Legacy systems often require expensive maintenance and support, while modern systems offer reduced operational costs, fewer manual interventions, and lower licensing fees, resulting in long-term savings.

Enhanced data security

New systems come with up-to-date security features that strengthen data security, protect sensitive information more effectively, and mitigate security vulnerabilities. This ensures compliance with current security standards, reducing the risk of data breaches and cyberattacks.

Greater scalability

Modern platforms make it easier to scale resources up or down as your business needs evolve, offering flexibility and agility that legacy systems simply can’t provide, especially in dynamic market conditions.

Simplified maintenance

With modern systems, updates, patches, and support are easier to implement, eliminating much of the technical overhead that often comes with maintaining outdated systems, freeing up IT teams for more strategic work.

Access to new technologies and digital transformation

Migration unlocks the ability to leverage cloud-native services, automation tools, and modern development practices, empowering businesses to innovate faster and integrate with the latest technologies, keeping them competitive.

What’s the cost of migrating a legacy system?

Expenses may include software licensing, infrastructure upgrades, development hours, and the data migration process itself. While the upfront investment can be substantial, a successful migration often results in long-term savings through reduced maintenance costs, lower licensing fees, and more efficient operations.

When planned strategically, the return on investment can outweigh the initial costs by delivering a more agile, secure, and future-ready system.

How do we measure success after a legacy system migration?

Measuring the success of a legacy system migration involves evaluating both technical performance and business impact.

Key metrics include improved system performance and uptime compared to the old system, as well as user adoption rates and satisfaction. A successful migration should also demonstrate cost savings, fewer incidents or service disruptions, and a smoother, more efficient workflow – even in the case of a complex system.

Most importantly, the new solution should align with business goals and support future growth. Tracking these outcomes ensures the complex process follows best practices and delivers real, measurable value.

FAQ

How long does a legacy system migration take?

The duration of a legacy system migration depends heavily on the size, complexity, and architecture of the existing system, as well as the chosen migration strategy.

Simple rehosting projects might take just a few weeks, while complex refactoring, rearchitecting, or full rebuilds can span several months or longer. Proper planning, resource allocation, and stakeholder alignment can significantly influence timelines.

Should we migrate everything at once or in phases?

If you are thinking whether to undergo a complete or partial transition, it’s worth knowing that migrating in phases is generally considered best practice, especially for large or complex systems.

A phased approach, such as the Strangler Fig Pattern, allows teams to gradually replace parts of the old system with new functionality. The Strangler Fig Pattern involves building new features alongside the legacy system and slowly replacing its components over time, minimising risks and ensuring the new system integrates smoothly.

This method enables continuous testing, early issue detection, and incremental value delivery, avoiding the disruption of a full system cutover. It also allows for greater flexibility, making it easier to adapt to changing requirements throughout the migration process.

How do you ensure data integrity during migration? What are the best practices?

Ensuring data integrity is a critical part of any legacy system migration process, as any data loss can have serious consequences.

This involves using automated data validation scripts, maintaining synchronisation between old and new systems during cutover, conducting rigorous pre- and post-migration testing, and keeping secure backups of all legacy data. The goal is to ensure that no data is lost, corrupted, or misaligned during the transfer.

Can I migrate legacy systems to the cloud? Why cloud migration may be a good idea?

Yes, migrating legacy systems to the cloud is a widely adopted strategy for modernisation. Cloud platforms such as AWS, Microsoft Azure, and Google Cloud offer robust tools and infrastructure to support various types of system migrations, from rehosting to full rearchitecting.

Cloud migration enables organisations to scale more efficiently, improve performance, and reduce reliance on aging on-premise hardware.

What role does business continuity play in migration planning?

Business continuity is a core consideration in any legacy system migration strategy. To avoid disruption of essential services, ensure a smooth migration process and minimise any security risks, organisations should plan migrations during low-traffic periods, use dual-running environments, and prepare rollback procedures. Ensuring seamless access to critical systems throughout the migration process helps maintain customer trust and operational stability.