From Refactored to Cloud-Native: The Second Half of Mainframe Modernization

Part 2 of Astadia’s Modernization Series by Jordan Silk, Sales Director

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Modernizing COBOL-based mainframe systems is a critical first step—but it’s only half the journey. Refactoring legacy code and preserving business logic can liberate you from the constraints of the mainframe, but the true return on investment (ROI) emerges when those systems are transformed into modern, cloud-native digital products: elastic, observable, continuously deployable, and cost-optimized.

At Astadia, we don’t stop at refactoring. We apply a structured, tool-driven approach to re-architect your systems, ensuring they’re aligned with how modern enterprises operate today—modular, agile, secure, and built for rapid change.

Why Cloud-Native Is the Finish Line

Modern enterprises don’t just want their COBOL logic rewritten in Java. They need systems that can:

• Scale elastically during peak demand and scale down to save costs
• Withstand failure without disrupting end-users
• Deploy updates continuously, not quarterly
• Deliver transparency across infrastructure, application health, and spend

To achieve this, we evolve tightly coupled mainframe systems into cloud-native, microservice-based architectures—enabled by Kubernetes, GitOps, observability pipelines, and automated governance.

The Cloud-Native Modernization Flow

We use a five-phase flow to move from legacy applications to cloud-native platforms, supported by purpose-built tools and clear business alignment.

Step 1: Modularization & Service Blueprinting

We start by ingesting the entire legacy codebase—COBOL, JCL, copybooks, VSAM/DB2 schemas—into our tooling framework. This forms a complete semantic map of the system, uncovering program relationships, data dependencies, and execution flows.

From there, we construct a Service Blueprint for each functional area:

• Groups code by business capability (e.g., claims processing, pricing logic)
• Maps I/O flows and transactional boundaries
• Defines what the future service will look like, who consumes it, and how it fits into the larger architecture

What this means:

• The future state is not theoretical—it’s clearly defined
• Teams align early around structure, scope, and strategy
• Services are designed with maintainability, not just migration, in mind

Step 2: Containerization & Orchestration

Once refactored, services are packaged and deployed in a modern runtime environment:

• Built as containerized services with deployment artifacts
• Deployed to Kubernetes environments (EKS, AKS, GKE, OpenShift, or on-prem hybrid)
• Integrated with service meshes (e.g., Istio) to manage routing, security, and resiliency

What this means:

• Services can scale dynamically based on real-time needs
• Resilience is built in, reducing downtime risk
• Teams can deploy independently without coordination bottlenecks

Step 3: Continuous Integration/ Continuous Delivery (CI/CD) & GitOps Integration

We implement delivery pipelines that reflect tested modular and business processes:

• GitOps drives environment parity, version control, and auditability
• Automated testing ensures behavioral parity with legacy systems
• Canary and blue/green deployments support gradual rollout and rollback

What this means:

• The entire business process value chain is measurable
• Change velocity increases without losing control

Step 4: Observability & FinOps

We embed observability and financial insight directly into the platform:

• Metrics, logs, and traces feed centralized dashboards
• Service-level objectives (SLOs) guide performance monitoring
• Cost telemetry reveals spend at the service and environment level

What this means:

• Operations teams gain real-time insight into system health
• Finance teams gain visibility into cloud spend
• Leaders can make decisions based on measurable outcomes, not guesswork

Step 5: Security, Compliance & Governance

Security isn’t a bolt-on—it’s part of the pipeline:

• IAM and RBAC policies mirror legacy access models
• Data security policies include field-level encryption and key rotation
• Compliance frameworks (e.g., FedRAMP, HIPAA) are templated in infrastructure as code

What this means:

• Systems are segmented and standards are consistently applied to affected systems
• Security posture improves as systems modernize
• Compliance is built in from the start, not added later

What You Take to Production

At the end of this journey, you don’t just have refactored code—you have a modern digital foundation:

• Modular, cloud-native microservices aligned with business capabilities
• CI/CD pipelines and GitOps workflows ready for continuous change
• Observability and cost tracking built into every layer
• Audit-ready, security-first infrastructure
• A clear blueprint to scale and evolve

This is modernization not as a one-time fix—but as a platform for ongoing innovation.

What’s Next in This Series

Stay tuned for the next installments in our Modernization Series, where we’ll explore:

1. Parallel-Run & Cut-Over Validation: Proving behavioral parity under real-world load before the switch.
2. Migration-Phasing Playbooks: How to structure a safe, sequenced rollout from batch jobs to high-impact workloads.
3. Workforce Enablement: How we help internal teams own and evolve the new platform with confidence.

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Missed part 1? Read here

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Ready to explore what a modern future looks like for your mainframe systems?

Start the conversation today here