AWS Partner Network (APN) Blog

Demystifying Mainframe Modernization with Best Practices from AWS and Accenture

By Joel Rosenberger, Mainframe Modernization WW Technical Lead – Accenture
By Sameer Pakanaty, Mainframe Modernization WW GTM Lead – Accenture 
By Mahesh Jadhav and Paulo Coutinho, Solutions Architects – AWS
By Dan Spillane and Howard Hinman, Principal Partner Development Managers – AWS


Mainframe modernization can vary in meaning depending on the stakeholders involved. It’s crucial to grasp the business motivations behind mainframe modernization, such as cost reduction, talent risk, or agility to adapt and deploy globally.

Additionally, factors such as skill gaps, sustainability, system consolidation due to mergers and acquisitions, and upcoming events like mainframe or software renewal may drive the need for modernization.

Various paths can be taken to address the perceived need for modernization. Some consider moving existing mainframe applications to distributed or cloud platforms to reduce costs, enhance performance, and increase business agility as a form of modernization.

Others view rewriting or refactoring applications using a modern language/framework architecture as modernization. Replacing mainframe applications with commercial off-the-shelf services and software packages (COTS) is considered another approach.

Accenture frames the migration patterns in five categories:

  • Replatform (COBOL and PL/1 running on AWS)
  • Refactor (convert to Java)
  • Data augmentation (replication-change data capture (CDC), backup)
  • Replace (with SaaS)
  • Reimagine (custom rewrite, new greenfield development)

In this post, we will discuss how the Accenture AWS Business Group (AABG) simplifies mainframe modernization complexity with its Mainframe Zero Approach. Accenture, an AWS Premier Tier Services Partner and Managed Services Provider (MSP), offers comprehensive solutions to migrate and manage operations on AWS.

Rising Interest in Mainframe Modernization

With mainframes, there are typically five broad challenges that organizations face:

  • Lack of agility, speed, and scalability for businesses to deploy new solutions.
  • Ability to respond to evolving regulatory and compliance requirements.
  • High operating and maintenance costs.
  • Locking in data prevents monetizing intelligence.
  • Skills scarcity to support the interwoven technical debt.

As a result, mainframe modernization has become front and center for a growing number of organizations. These are some of the primary reasons customers are looking to modernize the workloads hosted on mainframes:

  • As the mainframe market has begun to shrink more rapidly, mainframe costs (including third-party mainframe software licenses) have been increasing to make up for the loss of revenues by mainframe hardware and software vendors.
  • Availability of mainframe modernization capabilities to simplify and accelerate a modernization journey. For example, AWS offers a unique platform (AWS Mainframe Modernization Service) that allows users to migrate and modernize on-premises mainframe applications to a cloud-native and fully managed runtime environment on AWS (consumption-based service).
  • The explosion of analytics, machine learning, virtual reality, and artificial intelligence can help monetize the data residing on the mainframe to drive business value.
  • Disruptive technologies and trends such as sustainability have additionally come to the forefront and are being encompassed in business planning.
  • Finally, the increasing scarcity of mainframe skills is threatening business continuity in mainframe shops.

Mainframe Zero Approach

A customer journey towards achieving “mainframe zero” by leveraging Accenture AWS Business Group (AABG) expertise serves as an illustrative use case. A multi-year initiative typically involves the migration, replatforming, refactoring, and data augmentation of mainframe-based applications on AWS.

The effort is highly collaborative, involving Accenture, AWS, and the customer team that manages legacy and emerging application systems. These programmers generally specialize in mainframe COBOL/PL1 and work within a classic CICS/COBOL/VSAM/DB2/IMS environment.

A project may also encompass other technologies, such as Assembler code, third-party utilities/databases, software packages, and complex multi-tier integrations with external environments, presenting additional challenges that are common in enterprise mainframe landscapes.

For example, a customer could be using MQ Series and CICS Web Services to enable mid-tier capabilities for mainframe-based applications. Service delivery may be extended through integration with modern web and graphical user interface (GUI), while batch applications may rely on File Transfer Protocol (FTP) for data assimilation and reconciliation with the mainframe. Untangling millions of lines of COBOL code and developing a new data model is a crucial step in transformation.

Recommended steps for a successful mainframe modernization program include:

  • Conduct comprehensive discovery, assess the environment and dependencies, develop data models, create the business case, and gain financial approval.
  • Break down monolithic mainframe apps into smaller, migratable components.
  • Develop the wave plan (the journey).
  • Define in detail the future state for agility, cost, and risk; consider interim and transient states.
  • Establish governance, anticipate culture change, and ensure resources for successful modernization.

Assessment and Discovery

To address the unique challenges faced by each mainframe customer, Accenture utilizes highly automated tools and accelerators which are integrated with AWS-native services to conduct a comprehensive analysis of the existing environment. This analysis encompasses applications, databases, and infrastructure, providing a holistic understanding. The primary focus is on identifying dependencies and interconnections between components to uncover potential challenges and risks.

Accenture also emphasizes the development of accurate data models to comprehend the data structures and relationships within the mainframe environment. This insight guides decisions regarding data migration, transformation, and integration during modernization.

The evaluation process combines the expertise of customer teams’ infrastructure, application and process subject matter experts (SMEs) with Accenture’s functional knowledge. By integrating these insights with automated tools, a thorough analysis is jointly developed. This forms the basis for a tailored strategy in the AWS Mainframe Modernization journey, considering each customer’s unique characteristics and challenges. A detailed business case is developed encompassing current cost models using inputs from the additional steps below.

When undertaking a large-scale mainframe modernization initiative, executive sponsorship, a well-defined funding model, and an established governance model are vital. The governance strategy should involve customer SMEs to ensure project progress, in addition to their ongoing responsibilities with mainframe applications. Finding the right balance allows their expertise to support the modernization team, even if they are not directly involved.

Accenture and AWS Professional Services provide experienced mainframe modernization team members who specialize in creating a business case using a proven methodology. This approach encompasses the mainframe, mainframe modernization, and AWS cloud pillars, avoiding analysis paralysis and failed proof of concepts (POCs) that lead to delays and wasted costs.

Assessing the financial benefits and return on investment (ROI) is crucial for the initiative’s success and viability. Accenture and AWS collaborate with the customer to evaluate the cost savings, increased agility, and strategic advantages of migrating to AWS. Together with the customer, Accenture and AWS develop a comprehensive business case that presents a compelling argument for the modernization initiative. This is presented to the management team, emphasizing the value proposition of the modernization initiative.

Untangling the Applications

Untangling applications for granular modernization and roadmap development is complex, and often influenced by two factors. First, data dependencies in the mainframe data model pose challenges for data separation. Intricate data replication strategies, called “parallel operations bridges,” are developed to ensure data integrity and smooth migration. Second, application dependencies and external interfaces are uncovered and mapped.

Assessing online applications, particularly CICS and IMS managed, are challenging due to dynamic application flows and numerous permutations. Accenture accelerates the application discovery process by integrating the AWS Mainframe Modernization assessment service with its own toolset. This proven approach incorporates profiling and transaction log analysis, identifies dead or unused code, and highlights the interdependencies between applications and data.

The output of this stage is a complete and categorized list of applications, based on factors such as technical complexity, criticality, dependencies, and business value. The iterative discovery process continues until production deployment, which allows teams to gain further insights of the applications during the modernization process.

Develop the Wave Plan (the Journey)

After assessing and categorizing applications follows the order determination of which applications should be migrated and modernized into AWS. Together, Accenture, AWS, and the customer establish clear criteria to determine each migration wave, considering factors such as application dependencies, data dependencies, risk tolerance, and business priorities.

These factors are specific to each customer and are considered input for the Wave Decision Framework, which accelerates the migration wave determination process by:

  • Dividing the applications into logical groups. Each wave should consist of a manageable number of applications that can be migrated within a specific timeframe.
  • Prioritizing the applications based on their dependencies, interconnections, and criticality.
  • Allocating necessary resources, including personnel, infrastructure, and budget, to each migration wave.
  • Identifying and addressing any dependencies or risks that may impact the migration plan.

The wave plan is continuously monitored by Accenture and AWS to track the progress of each wave and make adjustments as needed. The team regularly reviews and reassesses the migration wave plan to accommodate changes in priorities, resources, or business requirements.

Define Future-State AWS Architecture

Upon completing the assessment and discovery phase, a foundational architecture aligned with the AWS Well-Architected Framework is agreed upon to support modernization efforts across multiple waves. The wave plan, which may span multiple years, includes cost estimates for mainframe infrastructure and software renewal, aiming for early wins in Millions of Instructions Per Second (MIPS) reduction and delivering new capabilities to end users.

The diagram below shows how Accenture and AWS defined a target architecture that will receive the mainframe workloads.


Figure 1 – AWS target architecture for mainframe modernization.

  1. AWS Direct Connect provides dedicated network connectivity between customer data centers and AWS.
  2. Landing zone creation is accelerated using a joint AABG asset (Velocity – Secure Cloud Foundation). Accenture and AWS teamed up to build the Velocity solution, a continuous innovation engine that helps you add new cloud innovations up to 50% faster. Security, repeatability, automation, and flexibility are all built into industry-specific solutions at their core. ​
  3. MQ Broker provides application and data integration with the mainframe.
  4. AWS Mainframe Modernization runtime that hosts applications refactor by AWS Blu Age or replatform by Micro Focus Enterprise Suite.
  5. Amazon Relational Database Service (Amazon RDS) to manage the relational data and VSAM files migrated from the mainframe.
  6. Job Scheduling SW is used to manage batch jobs that run in the AWS Mainframe Modernization service.
  7. Business applications running on AWS integrate with AWS Mainframe Modernization applications.

The foundational architecture considers factors such as high availability, latency requirements, security guardrails, federated data replication strategies, relational database engine capabilities, and DevOps integration. AWS Mainframe Modernization plays a central role, supported by Accenture’s toolset and accelerators that also address non-functional requirements.

Analysis of common patterns such as error handling and logging identify opportunities to consolidate them on the cloud platform, thus simplifying modernization. Code clean-up opportunities are also recognized to reduce size and complexity before migration.

During the modernization journey, there may be chances to introduce changes to migrated applications. For example, if a complex custom address validation process is identified, a well-established address validation service can be leveraged in the cloud. While some custom work is needed for compatibility, the benefits offer enhanced functionality and reduce maintenance for the customer team.

Need for Organizational Change Management

One aspect often overlooked during the transition from the mainframe to the cloud is the impact on the organization and the importance of implementing a comprehensive program to facilitate the acquisition of new skills that enable the organization to evolve alongside the modernization efforts.

Accenture and AWS collaborate to assist customers in establishing a Cloud Center of Excellence (CCoE) that provides accredited training and certifications on various technologies and skills in public cloud management. This collaborative effort supports the mainframe transformation and cloud journey.


In this post, we discussed mainframe modernization, architectural patterns, and why there has been an increase in customer interest in mainframe modernization. We also shared how Accenture’s “mainframe zero” approach combine with automated tools to help simplify mainframe modernization on AWS.

Post-migration, a key aspect is the cloud operation of the migrated workload on AWS. Accenture offers improve service quality with Accenture Cloud Managed Services for AWS.


Accenture – AWS Partner Spotlight

Accenture is an AWS Premier Tier Services Partner and MSP that provides end-to-end solutions to migrate to and manage operations on AWS. By working with the Accenture AWS Business Group (AABG), a strategic collaboration by Accenture and AWS, organizations can accelerate the pace of innovation to deliver disruptive products and services.

Contact Accenture | Partner Overview | AWS Marketplace | Case Studies