Modernizing a Mainframe application - an example scenario

Overview

Legacy mainframe applications represent significant business value but often face challenges in meeting modern operational demands. Whether you’re planning a cloud migration, implementing containerized systems, or adopting modern development practices, CAST Imaging provides the analytical foundation needed to build a comprehensive transformation roadmap.

This guide outlines how CAST Imaging enables organizations to systematically approach mainframe modernization through data-driven insights and strategic planning.

The modernization challenge

Mainframe applications typically face several modernization hurdles:

  • Complex interdependencies between systems and modules
  • Ageing technology stacks with limited cloud compatibility
  • Unclear business logic buried in legacy code
  • Risk of business disruption during transformation
  • Difficulty quantifying modernization ROI

CAST Imaging: Your modernization partner

CAST Imaging transforms the modernization process from guesswork into strategic planning by providing comprehensive application analysis and actionable insights.

Core process overview

Application ingestion:

  • Deliver application source code to CAST Imaging
  • Configure analysis parameters for your specific environment
  • Execute comprehensive code analysis
  • Generate detailed application insights

Strategic planning:

  • Leverage built-in analytical features
  • Develop tailored modernization recommendations
  • Create risk-assessed transformation roadmaps

Five-phase modernization framework

Phase 1: Inventory and discovery

Objective: Establish a complete application landscape view

Activities:

  • Catalog all mainframe applications and components
  • Map interdependencies across systems
  • Document data flows and integration points
  • Identify external system connections

Phase 2: Business prioritization

Objective: Align technical transformation with business value

Activities:

  • Assess application criticality to business operations
  • Evaluate modernization ROI potential
  • Quantify risks associated with legacy maintenance
  • Establish transformation sequence priorities

Phase 3: Application analysis

Objective: Deep-dive technical assessment

Activities:

  • Analyze source code across languages (COBOL, PL/I, Assembler)
  • Examine data models and database structures
  • Evaluate batch processing and online workloads
  • Assess current system performance characteristics

Phase 4: Target architecture definition

Objective: Define modernization goals and target state

Options include:

  • Cloud-native applications: Fully redesigned for cloud platforms
  • Microservices architecture: Decomposed into independent services
  • Containerized applications: Packaged for consistent deployment
  • Hybrid approaches: Combining multiple modernization strategies

Phase 5: Business case development

Objective: Quantify costs, benefits, and risks

Deliverables:

  • Total cost of ownership analysis
  • Risk assessment and mitigation strategies
  • Timeline and resource requirements
  • Expected return on investment

Key CAST Imaging capabilities for modernization

Technology blocker identification

Challenge: Certain legacy components resist containerization and cloud migration.

Value: Proactively address migration obstacles before they impact project timelines and budgets.

Common Blockers:

  • Third-party components: EasyTrieve, REXX, and assembler modules. CAST Imaging’s Advisor feature automatically identifies problematic technologies:

  • CICS DataSets: Transaction-specific datasets incompatible with container platforms. You can easily locate these items using CAST Imaging’s objects and links display configuration in the right-panel:

  • Legacy middleware: Components requiring specialized runtime environments

Dependency analysis and application decoupling

Challenge: Mainframe systems often feature tightly coupled architectures that complicate modular modernization.

CAST Imaging’s dependency visualization reveals:

  • Inbound and outbound application connections
  • Data flow patterns between systems
  • Isolated applications suitable for independent modernization
  • Critical integration points requiring API development

Strategic benefits:

  • Increased flexibility: Modernize applications independently
  • Reduced risk: Isolate changes to minimize system-wide impact
  • Scalability: Enable targeted performance optimization

Transaction boundary definition

Challenge: Understanding discrete business functions within monolithic mainframe applications.

CAST Imaging provides transaction perimeter/scope analysis to:

  • Identify transaction boundaries within complex applications
  • Map business functions to supporting code components
  • Enable modular refactoring based on business logic separation

  • Leverage AI services to interpret transaction functionality and generate human-readable explanations of complex business logic:

  • Persist insights as annotations for future reference and team collaboration as a Post-It:

Dead code elimination

Challenge: Legacy applications often contain unused code that increases migration complexity and costs.

CAST Imaging identifies dormant code sections, enabling:

  • Reduced migration scope: Focus resources on active functionality
  • Lower operational costs: Minimize cloud infrastructure requirements
  • Simplified maintenance: Remove unnecessary code complexity

Software health assessment

Challenge: Code quality issues can compound during modernization, creating technical debt.

CAST Imaging’s comprehensive health metrics inform modernization approach about:

  • Code quality indicators highlight refactoring priorities
  • Security vulnerability assessment guides remediation efforts
  • Performance bottleneck identification informs architecture decisions

Conclusion

Mainframe modernization represents both significant opportunity and considerable risk. CAST Imaging transforms this challenge into a manageable, strategic initiative by providing the analytical foundation needed for informed decision-making.

Through comprehensive application analysis, dependency mapping, and strategic planning support, CAST Imaging enables organizations to confidently navigate their modernization journey while minimizing risk and maximizing business value.