AS400 Application Modernization: Detailed Guide

Introduction

Modernization of older systems is usually an attempt to develop an edge. In an industry full of legacy systems, the companies going through modernizations prior to others gain an early-bird advantage. But in some cases it’s not a proactive move, rather a business critical decision. For most companies still relying on them, AS400 Application Modernization falls into that category. The AS400 system, despite going through multiple updates, is now counted among legacy systems. Organizations that haven’t replaced them with more modern IBMi systems have to ensure that at least the applications running on the legacy systems are up-to-date. It’s worth noting that AS400 application modernization may occur with or without modernizing the underlying system, both of which have different cost, resource, and long-term business implications.

What is AS400 Application Modernization?

AS400 application modernization means improving/evolving/modernizing the applications built to run on legacy AS400 architecture to mimic some or all of the strengths, capabilities, and flexibilities of modern applications. However, it’s a broad definition and the actual application modernization process may differ greatly among businesses running AS400 applications on legacy systems. For some, it may simply be a shift from the Green Screen (the classic command-line interface) to GUI while keeping the application strictly on-premises. A more comprehensive modernization might include rewriting and refactoring the existing application extensively and migrating it to the cloud, even making it platform agnostic to an extent. This means minimizing its dependencies on the AS400 architecture, which may have some trade-offs but the modernization benefits usually significantly outweigh them.

Reasons to Modernize AS400 Applications

In software, like many other industries, the mantra “if it ain’t broke, don’t fix it,” works really well. And for many organizations that have AS400 applications serving their purpose exactly as they should, the application modernization might seem redundant. But that mindset can be fatal to growth. Many organizations are even pursuing IBMi application modernization to ensure that their applications are not slowing down their growth, and IBMi systems and their applications are modern compared to AS400 applications. There are several reasons to go for AS400 application modernization, including:

• Making the applications more user-friendly. Legacy applications can have longer learning curves without actually offering additional value. They are also less intuitive, making cross-training unfeasible.
• Making AS400 applications easier to maintain. Many of the applications designed for these legacy systems and architecture are written in languages that are becoming increasingly obsolete, like RPG and COBOL. Finding developers for these applications can become quite challenging, but modernization can get around this necessity.
• Most AS400 applications take advantage of the power and consistency these systems offer but they tend to be too grounded in the legacy systems. They are more challenging to integrate to modern tools and platforms. Modernization can make these applications more integrable.
• Modernization is crucial to make these applications run on cloud, which can be a dire business need. It also offers a wide range of cloud-related benefits, especially accessibility.
• While AS400 applications offer robust security when they are within their native environment, modernizing everything around them and forcing integrations to legacy applications may open security vulnerabilities. AS400 Application Modernization can ensure that the applications are also secure.
• You are going through a holistic AS400 modernization, application modernization becomes a natural part of it. The former is costlier and broader in scope compared to the latter.
• Sometimes it becomes a compliance necessity to modernize legacy applications, especially for businesses where digital compliance is quite stringent and rapidly evolving, like healthcare or medical.

Why Modernize Legacy AS400 System: Benefits of AS400 Application Modernization

AS400 Modernization is a significantly broader paradigm and has a comparatively massive scope. Like application modernization, one of the primary reasons to do that is legacy systems are difficult to scale and integrate with modern organization. This prevents them from taking advantage of technologies like cloud and Artificial Intelligence. Unlike application modernization, AS400 system modernization may require comprehensive strategies, including rehosting, refactoring, re-platforming, rearchitecting, and replacing. The benefits of a full AS400 overhaul or simply application modernization include:

• Applications become easier to scale, integrate, and maintain. This reduces developer cost and load and ensures that required expertise is readily available in the market, so the companies relying on these apps are not hit with talent shortage.
• The process also eliminates technical debt that sometimes goes unchecked for decades. This is a common issue with applications designed on and for legacy systems.
• Modernizing old apps afford them many of the benefits of modern applications, especially if they are redesigned the right way. These apps can be significantly faster, more accessible, easier to use and maintain. They might even become more microservice in nature, compared to their original monolithic structure.
• Once modernized, which can be a gargantuan task, the apps may become easier to keep up to date and constantly evolving.

All of these technical benefits culminate to a range of business benefits as well. Faster, modern, and more productive AS400 applications can ensure that business processes connected to them are more efficient.

What key challenges arise for AS400 Application Modernization?

The challenges associated with application modernization for this architecture are both complex and hail from several domains. The three most significant challenge domains are:

Technical Challenges

• Legacy Code Complexity – AS400 applications use RPG, COBOL, or CL, which are difficult to modernize.
• Monolithic Architecture – AS400 systems are often built as tightly coupled monoliths, making modularization difficult.
• Limited API & Integration Support – Native AS400 applications lack built-in RESTful API support, requiring middleware.
• Green-Screen UI Limitations – Traditional 5250 interfaces hinder user experience and require major rework for web/mobile enablement.
• Outdated Database Structures – DB2/400 databases often have flat-file structures and require schema redesign for relational or cloud databases.
• Incompatibility with Cloud & Microservices – AS400 applications were not designed for cloud-native or containerized environments.
• Data Migration Risks – Moving decades of data from AS400 databases to modern systems can be complex and risky.
• Performance Optimization Issues – Modernized applications must maintain or improve AS400’s high reliability and performance.
• Tooling Limitations – Existing AS400 development tools (RDi, SEU, PDM) have limited support for modern DevOps and CI/CD practices.

Skill & Resource Challenges

• Shortage of AS400 Developers – RPG and COBOL expertise is declining as experienced developers retire.
• Learning Curve for Modern Tech – AS400 teams must learn new languages, frameworks, and cloud platforms.
• Resistance to Change – IT teams and business users may be reluctant to replace or refactor legacy applications.
• Knowledge Transfer Risks – AS400 systems often lack proper documentation, making modernization efforts dependent on tribal knowledge.

Business & Operational Challenges

• High Modernization Costs – Rewriting or migrating AS400 applications can be expensive in terms of time, tools, and expertise.
• Downtime & Business Disruptions – Modernization efforts may cause temporary service outages or data inconsistencies.
• Regulatory & Compliance Concerns – Legacy AS400 systems often have embedded compliance logic that must be preserved in new environments.
• Lack of Clear ROI Justification – Decision-makers may struggle to quantify the benefits of modernization versus maintaining the status quo.
• Interdependency with Other Legacy Systems – AS400 applications are often linked to other legacy software, making partial modernization challenging.
• Data Ownership & Governance Issues – Ensuring data integrity and proper governance while modernizing databases and applications.
• User Training & Adoption – End users accustomed to green-screen interfaces may struggle to adapt to modern UIs and workflows.
• Security Gaps in Transition – Moving to modern environments requires security updates and compliance checks to prevent vulnerabilities.

Steps to Modernize AS400 Applications

The actual steps may vary based on the vendor selected for modernization. But in most cases, they would include the following steps:

1. Assessment & Analysis:

The first step is evaluating the existing AS400 applications to identify technical debt, outdated code and coding practices, code vulnerabilities, dependencies, etc. It’s also the time to conduct a thorough risk-benefit analysis of modernization in general and against the approach the vendor plans on taking.

2. Define Modernization Goals:

 It’s critical to ensure that the modernization goals are aligned with the business goals. Modernizing legacy apps just for the sake of modernization may not be a smart idea. Developing a road-plan based on business’s needs and long-term application use-cases is the right way to go.

3. Select Modernization Approach:

Once there is clarity on what needs to be done and why, it’s time to select the right modernization approach. For some businesses and systems, rehosting is the right way to go. It’s essentially a lift-and-shift to cloud platforms (e.g., IBM Cloud, AWS) with minimal code changes. Another common approach is refactoring, i.e., optimizing code for modern languages (Java, Python) while retaining core logic. A more aggressive though useful in the long-term approach is re-architecting, i.e., transitioning to microservices or containerized architectures (Docker, Kubernetes)

4. Data Migration & Modernization:

 App modernization isn’t an isolated process and naturally impacts all the data the app handles or has access to. The data can be migrated from legacy databases to the cloud completely or be processed through a hybrid system. It’s also modernized, cleansed (and in some cases, reformatted) to meet the modern data-base requirements.

5. UI/UX Modernization:

Old interface is one of the major drawbacks of legacy AS400 applications and evolving their interface to a more modern front-end is usually part of the modernization process. In some cases, the user interaction can be enhanced further by implementing responsive designs and developing role- based dashboards.

6. Integration with Modern Systems:

Many of the legacy applications for the AS400 systems were monolithic in nature and may need introduction of middle layers and integration with APIs to connect with a wide range of frameworks and systems.

7. Testing, Deployment, Monitoring, and Continuous Improvement:

Once the modern version of the legacy application is developed and designed, it should be rigorously tested for the environment it will be deployed in. The deployment is also typically carefully planned, regardless of whether it’s independent or running in parallel to an AS400 modernization. It’s also important to keep monitoring the modernized version of the app and to keep making improvements to fully realize the modernization benefits.

Technologies for AS400 Application Modernization

A wide range of technologies are used in AS400 application modernization, including:

Cloud Platforms:

• Public Cloud: AWS, Azure, IBM Cloud for scalable infrastructure.
• Hybrid Cloud: Retain on-prem AS400 for sensitive data while migrating non-critical workloads.

Programming Languages & Frameworks:

• Modernize RPG/COBOL code with Java, Python, Node.js, or .NET Core.
• Use low-code platforms (OutSystems, Mendix) for rapid app development.

Frontend Tools:

• Angular, React, or Vue.js for dynamic web interfaces.
• Mobile frameworks (Flutter, React Native) for cross-platform apps.

Integration Solutions:

• REST/SOAP APIs for seamless connectivity.
• Middleware like IBM ACE or Apache Kafka for event-driven architectures.

DevOps & Automation:

• CI/CD pipelines (Jenkins, Azure DevOps) for faster deployments.
• Containerization (Docker) and orchestration (Kubernetes) for scalable environments.

Database Modernization:

• Migrate DB2 to cloud-native databases (Amazon Aurora, PostgreSQL) or data lakes.
• Use ETL tools (Informatica, Talend) for data transformation.

Modernization Tools:

• Specialized tools like ASNA Visual RPG, Fresche Legacy, or Arcad Software for code conversion.
• Screen scrapers (Profound UI) to modernize 5250 interfaces.

AI/ML Integration:

• Embed AI capabilities (IBM Watson, TensorFlow) for predictive analytics or chatbots.

Security Enhancements:

• Implement IAM (Okta, Azure AD) and encryption tools for compliance (GDPR, HIPAA).

Cost of AS400 Application Modernization

The exact cost of AS400 modernization application and otherwise, is influenced by a wide range of factors. It also varies greatly from vendor to vendor. So instead of predicting the actual cost, it might be more useful to understand the factors influencing it:

• Scope of the modernization (whether it’s just application or systems as well).
• Approach taken, since some like rebuilding can be costlier than others.
• In-house vs. outsourcing also has a significant impact. The first might seem better from a cost-perspective, but if it leads to costly delays and mistakes, the cost would be significantly higher.
• Talent/labor cost, especially if you are outsourcing the task by the hour.
• Vendor you choose can have a significant impact on the cost.

It’s important to look beyond the direct costs as well. If someone can do the modernization but in several months instead of a few weeks, the time-cost might overshadow everything, especially if modernization is a business-critical decision.

How Programmers.io Can Help with AS400 Application Modernization

Programmers.io is a comprehensive digital services and software development company, with thousands of satisfied clients across the world. AS400 systems and more modern IBMi systems and applications are some of the company’s core specialities. The company boasts the world’s largest IBMi team with unparalleled legacy expertise. They can undertake and smoothly deliver on AS400 modernizations (application and otherwise), regardless of the complexity and comprehensiveness of the modernization needs. The company also possesses expertise in AS400 application development, allowing them to bridge the gap between modern and legacy more effectively.

Conclusion

AS400 application modernization can be a powerful and impactful business decision that still relies on legacy hardware, architecture, and applications. This can ensure that at least the application end of their digital infrastructure is modernized and ready to leverage the full potential of technologies like cloud and artificial Intelligence. However, it can be a complex undertaking, and without an experienced partner leading the project, the probability of failure and delays is quite high. So if you have decided to modernize your legacy AS400 applications, you should start focusing on finding the right company for the job.