The Migration of legacy systems may seem straightforward in concept, take information in an older system and put it in a newer one. The process of a migration of legacy systems, however, is anything but straightforward, and can cause a lot of headaches for your organization. While stakeholders may not look forward to the migration of legacy systems, it’s an important step in modernizing and improving the utility and functionality of an organization.

In this comprehensive guide, we’ll cover the basics of the migration of legacy systems, the benefits, some challenges, and the first steps necessary to begin migrating legacy systems.

What is a legacy system?

A legacy system refers to any software, application, or technology stack that, while once cutting-edge, has now become outdated. These systems are characterized by their antiquity, having been deeply integrated into the business processes over years or even decades. Despite their reliability and the critical functions they serve, legacy systems often pose significant challenges due to their incompatibility with modern technologies, high maintenance costs, and limitations in responding to new business needs.

DOOR3 has worked on a variety of different legacy systems,and they can vary widely across industries and organizations, depending on several factors such as the organization’s age, the industry sector, historical IT investments, and specific business processes. Here are some key points regarding the diversity of legacy systems we’ve seen in our past two decades of business:

Legacy systems are often built on outdated programming languages such as COBOL, FORTRAN, and RPG. However, “legacy” can also apply to systems built on earlier versions of currently used languages like Java and .NET, which may no longer be supported or compatible with modern platforms.

Legacy systems can range from monolithic architectures, where the entire application is tightly integrated, to early attempts at service-oriented architectures (SOAs). Data formats can also vary significantly, from flat files to hierarchical databases, requiring sophisticated mapping and transformation when migrating legacy systems.

The systems may be hosted on a variety of platforms, including mainframes, minicomputers, and early server architectures. Each hosting environment presents unique challenges for data extraction, performance optimization, and integration with modern cloud-based services.

The problems of legacy systems

All software participates in a lifecycle similar to our own; there’s birth, life, and death; all of this is guided by a technology aging process, which generally follows a path similar to organic life. And very much like organic life, software systems also experience a period of maximum output and value – may it be long! Once that occurs, it’s a slow and sometimes painful process of becoming less utilized, less supported, and less efficient. This is the beginning of the code rot and value decay, which will inevitably lead to the deterioration of the code that once made a piece of software so valuable.

As code rot continues, the software can eventually become a critical risk to the technological infrastructure as a whole. One wrong set of environmental circumstances could topple the entire system.

The ripple effects of a legacy system can be huge, and could have a major impact on your business.

Code rot is not the only concern for legacy systems, in fact rot can contribute to the following deficiencies.

1. Technical debt and obsolescence

Legacy systems often run on outdated hardware and software that are no longer supported by vendors. This leads to technical debt, where the cost of system maintenance and the risk of failures increase over time.

Integration difficulties: As businesses adopt new technologies, integrating these with legacy systems becomes increasingly complex, often requiring custom-built interfaces that are costly and difficult to maintain.

2. Limited scalability

Legacy systems were not designed for today’s digital demands. They struggle to scale effectively to handle increased loads, resulting in performance issues and degraded user experiences.

3. Security vulnerabilities

Older systems may not comply with current security standards, making them susceptible to breaches and data theft, which can have dire financial and reputational consequences.

4. Compliance and regulatory risks

With evolving regulations around data privacy and security, legacy systems pose a compliance risk, as they may not have the necessary controls to meet new legal requirements.

4. High maintenance costs

The costs associated with maintaining legacy systems are not just financial; they also include the opportunity cost of not investing in more efficient, modern solutions.

When speaking about the problems associated with legacy systems, our Founder, Alex Asianov, had this to say:

“Legacy systems represent a dual challenge. On the one hand, migration to a new system is easier if that new system is similar to the legacy system in areas such as (for example) the database structure). On the other hand, the ability to capitalize on the technological advances and improved utility of a modern system often requires a departure from the past, in turn complicating migration. Addressing this dilemma means making choices involving processes, data, user interfaces, deployment practices, support models, and almost every other aspect of software ownership and operation. DOOR3’s clear, experience-based judgment, combined with your perspective on your business and objectives are the two key ingredients that will make a legacy modernization and migration project successful and predictable”


What is a migration of legacy systems?

The migration of legacy systems refers to the process of transferring data, applications, and other technological assets from antiquated systems to modern ones. The migration of legacy systems covers both hardware and software transitions, but we will mainly reference software migrations in this guide. The breadth of a migration of legacy systems is expansive, covering everything from integration compatibility, platform shifts, or even replacing entire systems with a new custom version.

DOOR3 has countless different examples to look at when discussing the migration of legacy systems. Take the case of Stillwell-Hansen, a leading representative for HVAC manufacturers, DOOR3 was tasked with modernizing an outdated and cumbersome system. The challenge was not just about updating the software but ensuring that the new system streamlined operations, enhanced user experience, and supported business growth.

By developing a custom solution that automated key business processes and provided real-time data insights, DOOR3 helped Stillwell-Hansen achieve a significant improvement in efficiency and customer service.

By developing a custom solution that automated key business processes and provided real-time data insights, DOOR3 helped Stillwell-Hansen achieve a significant improvement in efficiency and customer service.

We could also look at our migration of legacy systems with DAA Enterprises Inc., which faced a unique challenge: their legacy system was limiting their ability to scale and adapt to changing market dynamics. DOOR3’s approach to their migration of legacy systems was to implement a modern ERP system that not only replaced the legacy system but also provided a robust platform for growth.

A legacy systems migration not only improved operational efficiency but also enhanced data accuracy and business intelligence capabilities, enabling DAA to make more informed decisions.

Siloed data more your cup of tea? Then you’ll love our work for Cadwalader, one of the oldest law firms in the United States. The challenge was to modernize their legacy document management system. The goal of their migration of legacy systems to improve document access, collaboration, and security while ensuring compliance with legal industry standards.

DOOR3 developed a solution that not only streamlined document management but also integrated seamlessly with the firm’s existing workflows, significantly enhancing productivity and client service.

Each of these legacy migrations showcase how vastly different the impact of aging software can be on a business, and how each circumstance presents a unique set of challenges. Sometimes legacy systems migration can happen more gradually, particularly for systems that are only for internal use, other times, like for DAA, other approaches must be considered.

In our work with DAA we had a particular challenge to overcome, as the software being migrated was still being utilized by their customers. That plus the stringent regulations in the pharmaceutical industry meant that a phased approach would need to be implemented, first to create an MVP with core features that boosted usability, then to be followed with a future enhancement roadmap. Once that MVP was released to stabilize the overall experience, our work in overhauling the entire system could begin.

It’s adaptability like this that you want to see within your legacy software migration team. The migration of legacy systems can be tedious and surprising, so flexibility within the process is a key factor.

Reasons for the migration of legacy systems

There are many reasons to conduct a legacy systems migration, including increased efficiency, reduced maintenance costs, better scalability, and improved security. Some industries may see greater benefits than others, which you can learn more about in our 6 Industries Benefiting the Most from Legacy System Migration blog.

There are other, more specific, reasons why an organization may choose migrating legacy systems from one platform to another, but they tend to vary.

“As we navigate the complexities of legacy system migrations, it becomes increasingly clear that the ‘why’ behind each legacy software migration is as diverse as the industries we serve,” explains Laena Ilk, Director of Solution Architecture. “In healthcare, the push might come from a need for better data privacy and patient engagement platforms, while finance often seeks to improve transaction security and regulatory compliance. Meanwhile, retail companies look towards enhancing customer experience and omnichannel capabilities.

Understanding these industry-specific drivers for legacy software migration is crucial for tailoring our approach, ensuring that the solutions we implement not only resolve current limitations but also propel our clients towards future growth opportunities.”


You can learn more about these benefits by reading our piece on the 4 Reasons to Conduct Legacy Migration: Unlock Potential.

Roadmap for migration of legacy systems

While some common examples of a migration of legacy systems only have a few steps in the process, migrating legacy systems is anything but easy. The reintroduction of security risks, loss or corrupted data, and poorly planned rollout and rollback strategies can have a negative impact on your business. When beginning the process of data migration of legacy systems, it’s important to develop a detailed roadmap for your transfer.

These aren’t the only challenges organizations face when conducting migration of legacy systems, as potential roadblocks and pitfalls vary depending on the complexity of the move. Enterprise level companies are likely to have more difficulties based on the sheer size of the organization, although this means they have more resources to remedy these problems.

Smaller organizations have less complex data migration from legacy systems generally, but this comes with a smaller margin for error in their budget as well. Some factors that may further complicate a migration of legacy systems include complexity of the legacy system, compatibility issues, downtime and disruption, data quality and integrity, lack of resources, and employee overwhelm. All of these factors lead to delays in conducting the legacy software migration, which can lead to real world consequences.


Recent examples show this is not merely theoretical. In January 2023, both Canadian and US national flight management applications crashed at the same time. This not only resulted in thousands of delayed and canceled flights and millions of disrupted travelers, but also put both airline crews and passengers in dangerous situations.

In May of 2022 a surge in US bond buying crashed the TreasuryDirect site.

In 2018 the IRS computer system crashed delaying the processing of millions of returns.

All of these examples were totally preventable if a data migration from legacy systems had been conducted, with government officials acknowledging the risk sometimes years before the system meltdown, and every time something like this happens the price tag for recovering the system grows.

To learn more about the risks and challenges of the migration of legacy systems read our blog Legacy System Migration Challenges For Enterprises.


The DOOR3 migration of legacy systems process

The migration of legacy systems begins with a comprehensive assessment of the existing database system, understanding the scope and intricacies of the legacy database migration involved. This initial step is crucial for identifying potential challenges and planning the legacy system migration strategy accordingly. DOOR3’s expertise shines in navigating these complexities, ensuring a smooth transition with minimal disruption to business operations.

Strategic planning follows, where a detailed roadmap for the migration is developed. This includes defining the new architecture, planning the legacy database migration paths, and ensuring that all data integrity and security measures are in place. DOOR3’s approach to the migration of legacy systems emphasizes not just the technical aspects of the migration but also the business implications, ensuring that the new system aligns with the client’s operational needs and long-term goals.

The execution phase of a migration of legacy systems is meticulously managed, with DOOR3 overseeing the conversion process, data transfer, and integration with existing systems. Rigorous testing ensures that the legacy database migration meets all performance, security, and functionality requirements. This phase demonstrates DOOR3’s commitment to delivering a seamless migration experience, leveraging their technical prowess to ensure a successful transition.

Training and ongoing support are pivotal in DOOR3’s migration of legacy systems roadmap. Post-migration, clients are equipped with the knowledge and tools necessary to maximize the benefits of their new software. This ensures that users can effectively leverage the new system’s capabilities, with DOOR3 providing continued support to address any emerging needs or challenges.

The blog on migrating and converting Access to SQL Server encapsulates DOOR3’s comprehensive approach to legacy system migrations, highlighting our expertise in creating customized plans that cater to the unique needs of each client. Through careful planning, execution, and post-migration support, DOOR3 ensures that businesses can transition to modern, efficient systems that drive operational excellence and innovation.

DOOR3’s approach to legacy system migration is highly customized, reflecting their understanding that each legacy system, and the business it supports, presents a unique set of challenges. This tailored approach to the migration of legacy systems ensures that the migration roadmap is not only strategic but also adaptable to the specific requirements and constraints of each project. Here’s how DOOR3 tailors roadmaps to address the unique challenges presented by each legacy system:

Role of technical discovery during a legacy migration

To minimize the impact of roadblocks during this process, a technical discovery may be in order.

A technical discovery is the initial first step in a migration of legacy systems with DOOR3. This preliminary step is a smaller expense and allows for our team of engineers, business analysts, and consultants to conduct a comprehensive assessment of the work required to complete a successful data migration from legacy systems and a realistic timeline to do so.

A technical discovery also analyzes any potential risks or pitfalls that could occur during the process. This discovery phase looks at the project from a holistic perspective, and analyzes any areas within your business that may be affected by taking on the project. This may include inspecting the age of legacy systems and their last formal support offerings from developers, custom code compatibility with modern platforms, and your organization’s overall technology objectives as well as short-term and long-term goals.

Our experts build the legacy software migration roadmap for you, so that you know exactly how long and how much something like this will take. That way when you’ve got the resources to execute the project, you can do so swiftly and with full confidence.

Once the analysis portion of the discovery process is complete, our team shares our findings over a series of meetings. This may include recommended systems to migrate and where to migrate them to, and a roadmap for the unique legacy application migration process of your organization.

DOOR3 technical discoveries are an integral part of our process for the migration of legacy systems. For example, the technical discovery phase DOOR3 conducted for Stillwell-Hansen was critical to the project’s success, serving as a strategic foundation for the entire legacy application migration process. This initial phase allowed DOOR3 to dive deep into the existing legacy systems, uncovering specific requirements and challenges that needed addressing.

Understanding the intricacies of the old system was key to designing a legacy application migration plan that not only resolved current inefficiencies but also positioned Stillwell-Hansen for future growth and technological advancement.

By tailoring the legacy system migration strategy specifically to Stillwell-Hansen’s needs, DOOR3 ensured that the new system would seamlessly integrate with the company’s existing workflows and operations. This careful planning and execution meant that the migration could enhance operational efficiency, improve customer service, and support the company’s business objectives without disrupting day-to-day activities.

Ultimately, the technical discovery phase highlighted DOOR3’s commitment to delivering customized solutions that align with their clients’ long-term goals. Through a thorough understanding of Stillwell-Hansen’s operational needs and challenges, DOOR3 was able to implement a solution that not only addressed the immediate issues posed by the legacy systems but also laid the groundwork for ongoing improvements and success.

While the discovery process is unique to DOOR3, other providers have auditing processes for your systems as well. Never undercut the amount of time you provide for auditing your systems, as doing so can cause harm to your organization during the migration process.

How to undertake the migration process

We recognize that all these legacy system migration challenges are intimidating to the uninitiated, but legacy migration solutions are a necessary reality for organizations utilizing technology stacks within their business. Educating yourself and your team on the risks and strategies to navigate them will only result in more successful legacy migration solutions.

Migrating legacy applications without damaging critical data is possible, and DOOR3 has helped clients to do so countless times. With a keen eye on attention to detail, organizations can improve security, flexibility, and efficiency through the modernization of technology systems.

That being said, we never advise clients to try to take this work on by themselves, even after going through a discovery phase. Bringing in third-party specialists while migrating legacy applications will minimize risk of complication during the migration. Education on the process however, is still useful, empowering an organization to navigate legacy database migration conversations with ease.

To help with further educating you on the migration process, here are the five basic steps of conducting a migration of legacy systems.


To learn more about these five steps, read our blog Legacy System Modernization Approaches To Improve Software. In this piece we also discuss three common approaches to the migration of legacy systems: replatforming, refactoring/re-architecting, and rebuilding/replacing.


DOOR3 insights for legacy migration solutions

Here’s are some of the key strategies that have proven particularly effective for DOOR3 over the last few decades:

Thorough technical discovery and assessment

The importance of a comprehensive technical discovery phase cannot be overstated. This step allows DOOR3 to gain a deep understanding of the existing legacy systems, their architecture, and the business processes they support. By identifying the specific needs and challenges of each project, DOOR3 can tailor their legacy system migration strategy to ensure a seamless transition.

Customized legacy migration solutions

DOOR3’s approach to creating customized legacy migration solutions based on the unique requirements of each client has been a critical success factor. Tailoring the legacy application migration plan allows for addressing specific operational needs, ensuring that the new system enhances business processes and supports future growth.

Agile methodology

Employing an agile methodology when migrating legacy applications has allowed DOOR3 to remain flexible and responsive to changes throughout the migration process. This approach facilitates ongoing communication with the client, ensuring that the project can adapt to new insights or evolving business needs as they arise.

Focus on data integrity and security

Ensuring data integrity and security during the legacy database migration process is paramount. DOOR3 implements robust data migration strategies that include comprehensive data mapping, cleaning, and validation processes. By prioritizing data security, DOOR3 mitigates the risks associated with transferring sensitive information, ensuring compliance with industry standards and regulations.

Comprehensive post-migration support

Providing extensive post-migration support, including training for end-users and ongoing system optimization, ensures that clients can fully leverage their new systems. DOOR3’s commitment to post-migration support has been instrumental in facilitating smooth transitions for their clients, enabling them to quickly realize the benefits of their new systems.

Leveraging modern technologies

DOOR3’s expertise in modern technologies, including cloud platforms and contemporary development frameworks, ensures that migrated systems are scalable, efficient, and ready to meet future demands. This forward-thinking approach prepares clients for long-term success, allowing them to adapt to technological advancements and market changes.

By incorporating these strategies, DOOR3 has successfully navigated the complexities of legacy system migrations across various industries. Our tailored approach, combined with a commitment to quality and client satisfaction, has yielded positive outcomes for businesses seeking to modernize their IT infrastructure.

A successful legacy migration

With all these factors considered, you are ready to begin the process of upgrading your current technology stack with modern systems aiming to boost your organization’s operational capability. As the capabilities of modern technologies continue to expand, legacy systems migration will become more and more frequent, and those unwilling to adapt will be left behind. Stay ahead of your competitors and invest in your operational technology. Reach out to us here to learn more about how DOOR3 can help you through the legacy systems migration process.


1. What is a legacy system?

A legacy system refers to outdated computer systems, software, or technology still in use, despite newer alternatives being available. They are often critical to daily operations but may lack modern features, efficiency, or support.

2. Why should a business consider a migration of legacy systems?

Businesses might consider a migration of legacy systems to improve efficiency, reduce costs, enhance security, and ensure compatibility with modern technologies. A migration of legacy systems can also offer improved scalability and access to new functionalities that support business growth.

3. What challenges are typically associated with legacy systems?

Challenges include high maintenance costs, compatibility issues with new technologies, difficulties in updating the system, security vulnerabilities, and a dwindling pool of knowledge or support for outdated technologies.

4. How does DOOR3 approach the migration of legacy systems?

DOOR3 employs a structured approach to the migration of legacy systems that includes assessment, strategic planning, customized solution design, phased implementation, and rigorous testing. Our focus on minimizing business disruption and ensuring the new system aligns with our client’s long-term objectives.

5. What is the role of technical discovery in the migration of legacy systems?

Technical discovery is crucial for understanding the existing system’s architecture, dependencies, and limitations. It informs the legacy system migration strategy by identifying the specific needs, potential challenges, and the best methodologies for the migration.

6. How can DOOR3 ensure a smooth transition for end-users during a legacy system migration?

DOOR3 ensures a smooth transition through comprehensive training, support, and by implementing a user-centric design in the new system. We focus on minimizing disruption and addressing user feedback throughout the process.

DOOR3 has a portfolio of case studies on our website, highlighting our expertise in navigating complex migrations across various industries.

8. What are the steps involved in how to migrate legacy applications to cloud solutions?

A migration from legacy systems to cloud solutions involves a strategic process to transition from outdated systems to modern, cloud-based platforms. The journey of migration from legacy systems to cloud solutions begins with a comprehensive assessment of the legacy applications to understand their architecture, dependencies, and the specific challenges they present.

A successful migration from legacy systems to cloud solutions requires careful planning, which includes selecting the right cloud provider, determining the most suitable cloud model, and deciding on a migration strategy (rehosting, refactoring, rearchitecting, or rebuilding). Throughout the migration from legacy systems to cloud solutions, it’s crucial to ensure data integrity and security, requiring meticulous data migration strategies and the implementation of robust cybersecurity measures.

For organizations looking to embark on this transformative journey, understanding the intricacies of migrating legacy applications to the cloud is the first step towards unlocking new potentials and driving digital innovation.

9. How does DOOR3 ensure data security during the migration of legacy systems?

DOOR3 prioritizes data security by employing robust encryption, secure data transfer protocols, and compliance with industry-standard data protection regulations throughout the migration process.

10. What post-migration support does DOOR3 provide?

Post-migration support from DOOR3 includes system monitoring, troubleshooting, user training, and ongoing optimization to ensure the new system continues to meet the business’s evolving needs.

11. How long does a typical migration of legacy systems take with DOOR3?

The duration varies depending on the migration’s complexity, the legacy system’s size, and the new system’s requirements. DOOR3 provides a project timeline after the initial assessment and planning phases.

12. How can a business prepare for a legacy system migration with DOOR3?

Preparation involves cataloging existing data and processes, setting clear business objectives for the migration, and engaging stakeholders to ensure alignment and support throughout the project.

13. Can DOOR3 handle any migration of legacy systems, regardless of its complexity?

DOOR3 is equipped to handle a wide range of legacy systems, tailoring our approach to address the specific challenges and complexities of each project.

14. What technologies does DOOR3 typically migrate legacy systems to?

DOOR3 migrates legacy systems to modern platforms and technologies, including cloud-based solutions, contemporary databases, and the latest programming frameworks, depending on the project’s requirements.

15. How does DOOR3 handle unexpected challenges during a legacy system migration?

DOOR3 employs agile methodologies during a migration of legacy systems to adapt to unexpected challenges swiftly, ensuring project continuity through risk management strategies and flexible planning.

DOOR3 stays informed through continuous learning, industry engagement, and leveraging partnerships with technology leaders to incorporate the latest best practices and innovations in their migration projects.

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