Cloud Migration Checklist: From Legacy to Modern Infrastructure

Why Migration Strategy Matters

Cloud migration is one of the most impactful infrastructure decisions an enterprise can make — and one of the riskiest to get wrong. Done well, it unlocks scalability, reduces operational overhead, and enables modern application architectures. Done poorly, it creates technical debt, cost overruns, and operational nightmares.

The difference between success and failure usually comes down to planning. Here's a practical checklist organized into four phases.

Phase 1: Assessment and Planning

Before moving anything, you need a clear picture of what you have and where you're going.

Inventory and Discovery

Application catalog. Document every application, its dependencies, data stores, and integration points. You can't migrate what you don't understand.
Infrastructure baseline. Map current compute, storage, and network resources. Establish cost baselines for comparison.
Data classification. Identify sensitive data (PII, PHI, financial) and understand compliance requirements that affect where and how it can be stored.

Strategy Selection

Not every workload should be migrated the same way. For each application, evaluate:

Rehost (lift and shift): Move as-is to cloud VMs. Fastest, lowest risk, but doesn't leverage cloud-native capabilities.
Replatform: Make minor modifications to leverage managed services (e.g., moving from self-managed databases to RDS or Cloud SQL).
Refactor: Redesign for cloud-native architecture (containers, serverless). Highest effort but greatest long-term value.
Retire: Decommission applications that are no longer needed. Every migration is an opportunity to reduce complexity.

Business Case

Define clear success metrics: cost reduction, performance improvement, developer productivity, time to market.
Build a realistic cost model including cloud services, migration tooling, training, and temporary dual-running costs.

Phase 2: Foundation and Security

Build a secure, well-architected cloud foundation before migrating workloads.

Landing Zone Setup

Account/subscription structure. Design a multi-account strategy that separates environments (production, staging, development) and business units.
Networking. Establish VPCs/VNets, subnets, peering connections, and hybrid connectivity (VPN or Direct Connect/ExpressRoute) to on-premises systems.
Identity and access. Implement centralized identity management with single sign-on and role-based access control. Apply least-privilege principles from the start.

Security Baseline

Enable cloud-native security services (GuardDuty, Security Center, Security Command Center).
Configure logging and audit trails (CloudTrail, Azure Monitor, Cloud Audit Logs).
Implement encryption standards for data at rest and in transit.
Define and enforce security policies through infrastructure as code.

Infrastructure as Code

Choose your IaC tooling (Terraform, Pulumi, CloudFormation, Bicep) and establish conventions.
Build reusable modules for common patterns (VPCs, Kubernetes clusters, databases).
Set up CI/CD pipelines for infrastructure deployment with proper review and approval workflows.

Phase 3: Migration Execution

With the foundation in place, begin migrating workloads in priority order.

Migration Waves

Wave 0: Non-critical internal tools and development environments. Use these to validate your migration process and tooling.
Wave 1: Well-understood, lower-risk production workloads. Build confidence and refine procedures.
Wave 2: Business-critical applications with careful cutover planning, rollback procedures, and stakeholder communication.
Wave 3: Complex, tightly coupled systems that may require refactoring.

For Each Workload

Document the migration runbook with step-by-step procedures.
Establish rollback criteria and procedures before starting.
Conduct performance testing in the cloud environment before cutover.
Plan for data synchronization during the transition period.
Communicate timelines and impacts to stakeholders.

Phase 4: Optimization and Operations

Migration isn't done when the workloads are running in the cloud. The real value comes from optimizing operations.

Cost Optimization

Right-size instances based on actual utilization data (not legacy sizing).
Implement auto-scaling for variable workloads.
Leverage reserved instances or savings plans for predictable workloads.
Set up cost monitoring and alerts with FinOps practices.

Operational Excellence

Implement comprehensive monitoring and alerting for all migrated workloads.
Establish SRE practices: SLIs, SLOs, error budgets, and incident management procedures.
Automate routine operations (backups, patching, scaling) to reduce toil.
Document operational runbooks and conduct team training.

Continuous Improvement

Regularly review architecture against cloud-native best practices.
Identify opportunities to adopt managed services and reduce operational overhead.
Plan iterative improvements — migration is a journey, not a one-time event.

Key Takeaways

Successful cloud migration requires upfront investment in planning, a secure foundation, disciplined execution, and ongoing optimization. The organizations that treat migration as a strategic initiative — rather than a lift-and-shift project — consistently achieve better outcomes.

Whether you're just starting your cloud journey or midway through a migration, a structured approach reduces risk and accelerates value delivery.