Decomposing legacy mainframe applications by using AWS Transform

Amazon Web Services (contributors)

October 2025 (document history)

AWS Transform for mainframe modernization uses generative AI to accelerate the transformation of your workloads from COBOL-based legacy environments to modern, distributed Java systems. The transformation relies on application decomposition, which is a critical process that breaks down complex, interconnected code into manageable, business-aligned modules. This approach reduces your migration risks and lets you incrementally update your core business systems to ensure continuity and innovation.

This guide explains how to use the AWS Transform modules for code decomposition and how to plan your migration for efficiency. It explores the key challenges in mapping technical components to business domains, examines why decomposition is essential for successful modernization, and provides a step-by-step walkthrough of the AWS Transform process.

Intended audience

This guide is intended for technical teams and business stakeholders who are involved in mainframe modernization projects, including:

• Application architects

• Migration specialists

• Technical decision-makers

• Business analysts

• Development teams who work on mainframe transformation initiatives

Objectives

This guide discusses two primary outcomes: creating a decomposition strategy and developing migration wave plans.

The decomposition strategy:

• Aligns technical components with business functions.

• Enables incremental modernization.

• Reduces migration risks.

• Improves system maintainability.

The migration wave plans help you:

• Estimate implementation costs.

• Set realistic timelines.

• Prioritize business-critical components.

• Plan resource allocation.

• Define measurable success criteria.