Ultimate Guide to AS400 Migration to Cloud

Introduction

Undoubtedly, AS400 has been an integral aspect of enterprise computing, helping companies across various industries run some of the most significant operations. Nonetheless, the business and technology landscape has evolved and AS400 has to play catch up with the current trends.

AS400 is strong at stability, running for several years with barely any unplanned downtime. However, it is not designed for the flexible, intertwined world most companies now operate in.

Modern businesses need to respond quickly to changes and scale up or down based on demand. Organizations also want an interconnected tech stack where their systems can communicate with each other. Such requirements are barely met by the legacy AS400 systems and the only means to achieve them is through modernization and migration is one of the ways one can get there.

There are many tried and tested migrations pathways and some of these include rehosting on modern infrastructure, refactoring applications, or rearchitecting the entire system using microservices, APIs, and modern languages. While these achieve the goal of modernizing AS400, the business logic and data are untouched.

Irrespective of which pathway you choose for migration, understanding AS400's capabilities and future potential is crucial.

Understanding AS400 Systems

AS400’s system architecture was entirely built by IBM in which every part of the system (hardware, operating system, database, and even programming environment) was designed to work optimally with each other. This cohesiveness results in a highly stable environment with fewer bugs, crashes, and performance bottlenecks.

The AS400 runs on IBMi operating system which is tightly integrated with the hardware, in that the OS knows exactly how the hardware behaves and was specifically designed to work with AS400 hardware, and vice versa.

AS400 supports a wide variety of programming languages which is particularly useful when it comes to developing applications. One of the advantages of AS400 is that all the languages interact equally well with the same object-based architecture, DB2 database, and single-level storage and are deeply optimized for AS400’s hardware and OS.

Despite its several advantages, its legacy nature brings with it several limitations. One of the major limitations in today’s digital milieu is AS400’s inflexible nature to be readily integrated with modern cloud services, APIs, or front-end applications. Another major limitation is that the system isn’t readily scalable (up or down) based on the demand.

Adding to the woes, maintaining AS400 is becoming increasingly costlier due to limited availability of skilled professionals and aging hardware. Software updates and vendor support are also becoming increasingly difficult to manage.

Overcoming these limitations is the reason why companies choose to modernize their AS400 systems and moving to cloud is one of the ways. In doing so, companies can future-proof their aging AS400 systems while making use of its robustness.

Why Migrate to Cloud?

Legacy AS400 systems will eventually be unable to handle the changing needs of a business. Consequently, migrating to new, modern cloud infrastructure is key to innovating, gaining efficiency, and growing the business for the long haul. Here are some of the business reasons to migrate from AS400 to cloud:

Overcome Legacy System Limitations

Despite their stability, AS400 systems are long overdue for an upgrade when compared to today's computing standards. This is due to monolithic architecture of the system and the ageing hardware which slows down processing speed and limits efficiency. This makes it hard for businesses to manage large-scale operations.

Migrating to the cloud removes the dependency on legacy hardware. Cloud offers extremely flexible computing resources that can be scaled on demand and be continually updated for performance.

Business Growth Needs

Digital transformation has become imperative for businesses to stay competitive and keep pace with technological advancements. AS400 systems lack the ability to scale and to integrate with modern technologies.

Due to this many organizations fail to embrace modern technologies like cloud computing, AI and advanced analytics on AS400 systems. Such limitations stifle innovation and business growth and make modernization imperative.

Migrating to the cloud not only enables this integration but also provides access to a rich ecosystem of cloud-native services and tools that accelerate innovation.

Cost Efficiency

An AS400 environment can be expensive to maintain due to the costs associated with IBM i licensing fees, proprietary hardware, and specialist support staff. Migrating to cloud or hybrid models greatly lowers infrastructure and operational costs whilst providing superior performance and scalability. Cloud platforms also offer pay-as-you-go pricing models and the flexibility to choose a scale appropriately based on current demand.

Security & Compliance

Legacy AS400 systems do not have the advanced security features that the modern generation of cybersecurity threats requires.

Working in a modern data landscape and not being up to date with security measures makes is major threat to business. Without contemporary security tools and monitoring capabilities, complying with industry regulations and data governance requirements is extremely challenging.

Modern cloud platforms offer built-in compliance frameworks, advanced threat detection, automated patching, and encryption services that meet evolving regulatory standards.

Overcome Challenges Due to Talent Shortage

Since veteran AS400 specialists are retiring, it becomes difficult to find the right professionals to maintain and upgrade these legacy systems. The shrinking workforce increases the cost of hiring and renders long-term maintenance impossible. That, in turn, can create operational risks and inefficiencies.

Since cloud environments are contemporary technology, they offer abundance of talent availability and more standardized skill sets. Cloud platforms also have community-driven support that significantly reduces long-term staffing challenges.

Preparing for Migration

Migrating AS400 to the cloud involves many vital stages that need to be planned and executed carefully so that the transition doesn’t affect business continuity and performance. Here are some of the important steps involved in migrating from AS400 to cloud.

Assessment and Planning

Migrating from AS400 to the cloud begins with a thorough assessment and planning. This typically involves evaluating your current AS400 environment and mapping application dependency to ensure that all connected systems move together or stay synced.

Understanding these things will help companies identify what should be lifted and shifted, what needs to be refactored, and what should be retired or replaced. It is also important to know business goals like scalability, integration, or cost efficiency with cloud capabilities.

In addition, it is also worthwhile to create a detailed migration roadmap covering timelines, resources, risks, and stakeholder involvement.

Choosing the Right Cloud Provider

An early and crucial step in migrating to cloud is choosing the right cloud provider. Some of the crucial factors that must weighed while picking the provider include:

• Compliance support and service-level agreements (SLAs)
• Pricing and compatibility with legacy systems
• Availability of migration tools

Making the right decisions in these factors has far reaching impact in the long run on several organizational metrics like cost, performance and business continuity.

Choosing a Migration Approach

Once the provider is selected, the next step is to choose an appropriate migration approach. Here are some of the common ways to migrate AS400 workloads

• 1. Rehosting – Involves moving apps as-is to cloud infrastructure with no change to the code. This method is quick, low in cost but doesn’t make use of the cloud capabilities to the fullest.
• 2. Replatforming – This approach has minor tweaks to apps so they run better in cloud but doesn’t change the core business logic. It's a balanced approach that improves performance without much effort.
• 3. Refactoring (or Rewriting) - This is a complete overhaul that involves redesigning or rewriting the app to be cloud-native. It entails a high investment but leverages the capabilities of cloud like automation and scalability so that the companies are future-ready.

Technical feasibility is an important aspect when choosing an approach since many apps may be too tightly bound to IBM i systems leaving you with limited options to migrate. Also, budget is another limiting factor as some methods can be expensive (like refactoring) and some that are economical (like rehosting).

It will also be necessary to expose the functionalities of legacy applications through APIs or even recompile or refactor applications. Doing this can make apps modular and compatible with cloud and helps integrate with cloud apps and services.

Data and application modernization

Once the migration approach is zeroed in, data and application modernization come next. To be compatible with modern cloud-hosted RDBMS platforms like SQL Server, PostgreSQL, or MySQL, it is necessary to extract, cleanse and transform data on AS400 systems.

This ensures that the data being migrated will be free of redundant, obsolete, or inconsistent data after decades of use. Additionally, data types, encoding and structures that were once native to AS400 will be ready for use in modern relational databases.

It will also be necessary to expose the functionalities of legacy applications through APIs or even recompile or refactor applications. Doing this can make apps modular and compatible with cloud and helps integrate with cloud apps and services.

Risk Management

An important part of migrating AS400 is to have robust risk management in place. Risks may come in various forms - it can be operational disruption, data loss or security breaches and system downtime.

Identifying risks that might be faced and strategizing to counter these risks reduces the impact on business operations and gives teams time to respond effectively.

To minimize the exposure to risks, organizations should implement contingency plans which can include but not limited to data backups, rollback procedures and real-time monitoring.

Strategies for Migrating AS400 to the Cloud

Migrating AS400 to the cloud has many pathways, all depending upon the business goals, how much companies can invest in the transition as well as the complexity of the applications and data being moved. Here are some of the tried and tested strategies of migration.

Rehosting (Lift and Shift)

Rehosting is a straightforward approach where AS400 workloads are moved to cloud-based infrastructure with minimal or no change to the application code. It basically involves hosting IBM i on a virtual machine or managed service in the cloud and users continue interacting with systems the same way through green-screen interfaces or existing job routines.

Because the applications and interfaces don't change, employees don’t have to adapt to new interfaces or features. This is a major benefit for businesses that rely on large operational teams.

Instead of rewriting or re-engineering applications, rehosting moves applications as-is to a new home, just running on cloud hardware instead of on-premise AS400 boxes. This process is relatively fast and cost-effective, making it a popular first step in cloud modernization.

Replatforming

Replatforming optimizes AS400 applications to work better on cloud while the core architecture like application’s structure, business logic, and interdependencies are left unaltered.

It typically involves modest changes to application like updating middleware, integrating cloud-native monitoring tools, or shifting databases to managed services.

Companies can reap performance gains by replatforming as it leverages faster, scalable cloud infrastructure and many operations can be offloaded to managed cloud services. At the same time, replatforming avoids the risks of rewriting applications to cloud which involves changing business logic as well as avoids the longer timelines and higher costs of rearchitecting applications.

Refactoring

DRefactoring involves breaking apart monolithic AS400 applications, which are often written in RPG or COBOL, into smaller, independent services. For example, instead of a single RPG program handling all aspects of billing, you might have separate services for invoice generation, tax calculation, and payment processing.

Refactored logic is then exposed via APIs so that different services, apps, or front-ends can interact with it. Refactored cloud-native systems are more modular as they work on one microservice without affecting others. They are also scalable since teams can independently scale components based on demand.

In a refactored architecture, teams can release features more frequently with lower risk in contrast to monolithic AS400 codebases where small changes often require touching large portions of code, testing end-to-end, and risking regressions which slow down innovation.

On the flipside, refactoring is a cumbersome process requiring longer timelines and higher upfront costs.

Hybrid Approach

Hybrid strategies combine elements of rehosting, replatforming, and refactoring so that companies can modernize in phases. Organizations can start with simpler workloads and progressively refactor more complex systems. This approach reduces risk, minimizes downtime, and enables continuous delivery of value throughout the migration process. Hybrid strategies are especially effective for enterprises with mixed workloads, helping balance operational stability with innovation and future-readiness.

Key Challenges in Migrating to Cloud

AS400 migration can be a challenging process that organizations need to carefully plan and implement for a smooth transition. Grasping the obstacles in migration is key to minimizing risk in operations. These are some common challenges faced during AS400 migration.

Data Migration Complexity

Transferring extremely voluminous historical data to cloud is one of the biggest challenges while migrating. This is because maintaining accuracy and consistency of data across environments can be technically demanding.

AS400 systems can hold tens or hundreds of millions of records and may also contain inconsistent or incomplete data due to changes in business logic over time.

Also, AS400 uses legacy encodings and structures that are not directly compatible with cloud and need to be converted into usable, readable structures. Extracting, cleaning, validating, and transferring such a huge volume of data without disrupting business operations is a no small feat.

Application Dependencies

AS400 applications are at the core of business processes and are tightly integrated with other enterprise systems. When migrating to the cloud, these dependencies must be carefully mapped and managed to prevent broken workflows or gaps in functionality.

In the cloud, this gets more complex, because database and business logic which were once run locally and coupled with just the IBMi environment will have to be run on different servers across regions and data centers.

Also, AS400 applications, which have monolithic codebases, will have to be rearchitected into microservices and containerized so that they can be easily deployed, scaled, and managed in the cloud.

Downtime & Business Continuity Risks

Migrating a live, production AS400 system to the cloud introduces significant business continuity risks. If the transition to cloud isn’t planned well and meticulously, it can have dire consequences like service interruptions, data sync issues, or even system failure, directly impacting operations and causing financial loss.

To mitigate these risks, businesses need a structured migration strategy, including phased rollouts, parallel testing, rollback plans, and robust backup mechanisms to ensure that downtime is minimized and that there is no impact on users or customer-facing services during the changeover.

Skill Gap

Migrating from AS400 to the cloud requires expertise in both legacy IBM i environments and a good degree of understanding of modern cloud or hybrid infrastructures. These are two very different skill sets.

Organizations frequently struggle with a shortage of professionals who understand both ends of the spectrum. This challenge often forces companies to partner with experienced cloud migration vendors or invest in training programs to upskill internal teams, especially in areas like cloud architecture, DevOps, and AS400 modernization.

Security & Compliance Issues

During migration, data will be in transit between on-prem AS400 to cloud storage. Without strong encryption, sensitive data can be intercepted during this transition. Once the system goes live in the cloud, companies will be operating in a distributed, internet-facing environment, unlike AS400 where they had full control of the hardware, network, and physical access.

As a result, strong identity and access controls like role-based access and MFA (Multi-Factor Authentication have to be maintained without fail to prevent breaches.

Moreover, ensuring compliance with industry regulations (like HIPAA, PCI DSS, or GDPR) becomes more complex in cloud environments since the responsibility to keep data secure is shared between the organization and the cloud provider.

In addition, businesses must reassess their security posture regularly after migration, which usually involves updating or replacing outdated and conducting risk assessments tests, and compliance audits.

Tools and Technologies for Migration

Migrating AS400 (IBM i) systems to the cloud is done with specialized tools that address different aspects of the migration journey right from moving databases and applications to security compliance and monitoring performance. They ensure the entire process of migration has minimal disruptions and reduced downtime while preserving functionality.

This section details some of the important tools and technologies that are involved in migrating AS400 to cloud.

Migration Tools

There are many tools for migration As400 applications to cloud which help in both rehosting and replatforming. Following are some of the popular migration tools.

Infinite i

Infinite i is a rehosting platform that mimics the original AS400 environment while hosting it on cloud infrastructure. It replicates the IBM i runtime environment, so existing applications can run on non-IBM platforms (like Windows or Linux) without needing to recompile or rewrite them.

It is particularly useful for AS400 (IBM i) applications written in RPG, COBOL, and CL, that need to be to run on modern cloud or Linux/Windows environments. Since Infinite doesn’t alter the source code, all existing workflows, logic, and behavior remain intact.

Moreover, since functionality remains the same, users and IT teams don’t need to be re-trained on new systems.

Azure Migrate

Azure Migrate provides an end-to-end migration platform for AS400 workloads. It can automatically scan the existing AS400 environment to identify applications, their dependencies, and system configurations.

Azure Migrate can also evaluate performance metrics, compatibility, and cloud readiness which helps in deciding whether workloads can be moved as-is or they need to be replatformed or refactored. It also estimates costs, risks, and resource needs involved in migration.

Azure provides IBM Power Virtual Servers that emulate the IBM i environment on Azure. These are useful for moving AS400 workloads to the cloud as well as migrating databases, and settings with minimal downtime.

Azure Migration Hub

AWS Migration Hub is a central dashboard offered by Amazon Web Services that helps organizations manage large-scale migrations especially when multiple tools are involved. The most notable feature of this platform is its support for multiple migration tools under one umbrella. For example, databases can be migrated via one tool and apps via another all within the same platform.

AWS Migration hub also comes with a plethora of other features that offer centralized visibility and tracking. Following are some of the important features of this platform:

Planning

Helps build a structured migration plan with timeline estimates and workload tracking.

Risk mitigation

Offers rollback options, health checks, and performance monitoring.

Centralized visibility

Tracks the status of all migration activities (e.g., server moves, database transfers) in one place, regardless of which tool is used.

Progress monitoring

Shows what’s been moved, what’s in progress, and what’s planned.

Application Modernization

Modernizing AS400 applications requires tools that can refactor legacy code and adapt it for modern architectures. These tools not only help modernize code but also integrate legacy systems with new cloud-native services and microservices. Following are some of the popular options to modernize AS400 applications:

• 1. Fresche Solutions offers code transformation tools that convert RPG and COBOL applications into modern languages like Java or C#.
• 2. LANSA provides a low-code platform for extending and modernizing IBM i applications, supporting web, mobile, and API development.
• 3. Profound Logic delivers modernization tools to convert green-screen interfaces to web-based UIs and restructure backend logic into modular, reusable services.

Conclusion

AS400 migration can be a game changer for enterprises that want to capitalize on the robustness of this legacy technology but want to keep pace with technological developments and promote innovation. Migrating to cloud has many pathways but each one of them has to meet business objectives, addressing legacy system dependencies, and ensuring robust data governance.

However, an undertaking such as AS400 migration should be approached with caution. AS400 might be old but the complexity of the legacy system shouldn’t be underestimated. Equally important are adequate stakeholder involvement in the transformation as well as robust change management.

Looking ahead, AS400 migration is being reshaped by emerging technologies. AI-driven code conversion tools, containerization, and low-code platforms are accelerating modernization. Organizations are able achieve scalability and modularity of applications with cloud-native architectures and microservices and DevOps practices have been instrumental in streamlining deployment cycles.

AS400 migration touches nearly every layer of the technology stack from infrastructure, applications to data, security, and operations. As technology evolves, AS400 migration will no longer be system replacement but a foundation for digital transformation.