AWS Mainframe Modernization
A service that refactors or replatforms mainframe COBOL/PL/I workloads on AWS, accelerating legacy system modernization
Overview
AWS Mainframe Modernization is a platform service for migrating legacy workloads running on mainframes - COBOL, PL/I, JCL, and more - to AWS. It offers Micro Focus (replatform) and AWS Transform for mainframe (refactor), with the choice between running existing code as-is on AWS or automatically converting it to Java. It emulates or replaces mainframe-specific execution environments including CICS, IMS, and batch jobs in the cloud. Note that AWS has announced the service is no longer open to new customers (existing customers can continue, as of October 2026); for new mainframe migrations, AWS points to AWS Transform and vendor-direct offerings as the recommended path.
Selection Criteria for Replatform vs. Refactor
AWS has announced that Mainframe Modernization is no longer open to new customers in both the managed runtime environment and the self-managed experience, and that existing customers can continue to use it (as of October 2026). Replatform uses the Rocket Software (formerly Micro Focus) engine to move the application to a runtime environment on AWS, recompiling much of the source code without changes. Because fewer code changes are needed, it tends to keep migration risk and duration down. However, the codebase remains legacy, limiting long-term maintainability improvements. Refactor, which the user guide describes as powered by AWS Transform for mainframe, automatically converts COBOL applications into Java-based applications with an Angular-based front end and an API-enabled Java back end. Converted code can be maintained with modern development toolchains (IDE, CI/CD, test frameworks). As selection criteria, refactoring suits business-critical systems intended for long-term operation, while replatforming suits systems approaching EOL (End of Life) or early phases of staged migration.
Migrating Batch Jobs and Transaction Processing
Mainframe batch processing (JCL jobs) is managed by Mainframe Modernization's batch scheduler. The replatform approach interprets and executes JCL as-is. Under the refactor approach, VSAM file and DB2 database access is replaced by a data layer that accesses modern data stores. CICS online transactions run in the Rocket Software runtime under the replatform approach, or are converted to an API-enabled Java back end under the refactor approach. Screens are converted to an Angular-based front end that end users access from a browser.
Testing Strategy and Staged Migration Patterns
In mainframe modernization, equivalence testing checks whether the migrated system returns the same results as the original system. The user guide includes capturing and managing test scenarios among the refactoring steps. One staged migration pattern is the Strangler Fig pattern. An API Gateway is placed at the front, routing requests for new features to modernized services on AWS while routing unmigrated feature requests to the mainframe via Direct Connect. Migration proceeds function by function, with the strategy of eventually reducing mainframe traffic to zero.
References (Official AWS Resources)
The primary sources for this page are the official AWS website and documentation. Check the official pages below for the latest specifications and pricing.
- AWS Step Functions official page
- Amazon Aurora official page
- AWS Lambda official page
- AWS Documentation (official)
If this page and the official documentation disagree, treat the official documentation as authoritative.