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AS400 Modernization: A Step-by-Step Guide to Future-Proofing Your Systems

Nov 22, 2023
Modernizing AS400 - A Step-by-Step Guide

Considering the extensive use of AS400 in the IT landscape and the diverse range of technologies, databases, and supporting software in play, organizations are actively seeking ways for AS400 modernization. The goal is to achieve higher scalability, enhanced agility, and cost-effectiveness.

IBM AS400, also known as ‘IBM iSeries’ or ‘IBMi’, is an application server that runs mission-critical legacy applications that are both expensive to maintain and operationally challenging. The emergence of newer technologies has intensified the need to modernize AS400 systems to unlock greater value.

This blog will delve into the challenges associated with modernizing AS400 systems, exploring various modernization approaches and functional architecture patterns to optimize the benefits of AS400 modernization.

Challenges in Modernizing AS400 Systems

Every organization utilizing AS400 systems aims to leverage and reap the benefits of the substantial amount of valuable information it holds. However, limitations such as a monolithic code base, 5250-based ‘Green Screens’, integrated business logic, and the high cost associated with server and OS upgrades present significant hurdles to the modernization process.

AS400 modernization can be complex and requires diverse methodologies tailored to each company’s unique requirements, risk profiles, and workload.

Common causes for delay in AS400 modernization projects are:

  • Lack of understanding of the existing AS400 application landscape
  • Absence of a clear business plan addressing future needs
  • Underestimation of the potential risks
  • Insufficient funding for long-term modernization projects
  • Availability of various types of Modernization patterns, such as – Re-Hosting, Re-engineering, Re-architecture, and Re-new to consider

A successful AS400 system modernization demands a well-defined strategy, a dedicated plan, a modernization methodology, and a future-proof architecture.

AS400 systems need a customized approach to reduce total cost of ownership (TCO), unlock hidden data insights, and enhance system agility while delivering consistent business value.

AS400 Modernization

Four Approaches to Modernization

  1. Re-Hosting: 

Migrates the AS400 legacy systems to a new cloud platform, aiming to cut costs and expand business operations.

This approach allows existing AS400 applications to run on a cloud-based platform, utilizing an AS400 emulator that includes a set of compiler and OS (operating system) services. Application programs, developed in RPG and COBOL for the AS400 environment and database, are migrated at the source code level. Subsequently, these programs undergo recompilation and execution on the AWS platform, including complete database (DB2/400) replication.

Additionally, third-party tools used by application components, spanning message queues, backups, schedulers, reporting, printing, and tape management, are transferred to the cloud.

  1. Re-Engineer

Allows re-engineering of existing applications in a modern way.

A significant portion of the AS400 application portfolio comprises batch jobs, including ETL data processing, EDI file processing, and ad-hoc report generation. While some are business-critical, many are of low business value and are suitable for migration to two cloud-based solutions: file-based or near-real-time processes.

In both processes, existing AS400 applications are modernized by sending physical files or real-time data streams to the AWS cloud. It enables customers to get additional data insights through reports stored in a cloud-based NoSQL database.

  1. Re-Architect: 

Leads to the development of a new application with similar or enhanced performance and functionality.

If an existing IBM i/AS400 application falls short of meeting future business requirements or fails to align with an agile target architecture, the reengineering or refactoring approach is used for modernization.

  1. Re-New: 

Empowers you to embrace DevOps and upgrade the existing programming language, database, and user interface versions.

For modernizing the user interface (UI), the 5250 screens are transformed into a web interface without modifying the existing application support.

Organizations have the option to enhance the application by upgrading its RPG and DB2 modules into modular and decoupled applications that are easier to maintain, accelerating modernization initiatives.


We explored approaches such as rehosting, re-engineering, re-architecture, and re-new for AS400 application modernization. These methods help organizations increase their business agility and performance and reduce costs and manual dependencies, enabling their IT to drive business growth.

If you’re considering modernizing your IBMi/AS400 applications, contact our AS400 experts today.

Let’s discuss your project. Connect with us.

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