AWS Cloud Migration: What It Is and When to Use It

Definition

AWS Cloud Migration is the process of moving an organization's digital assets—such as applications, data, and infrastructure—from an on-premises environment or another cloud provider to the Amazon Web Services (AWS) Cloud. The primary goal is to leverage AWS's scalability, cost-efficiency, security, and vast portfolio of services to accelerate business innovation and improve operational resilience.

How It Works

A structured cloud migration follows a proven methodology, often guided by the AWS Cloud Adoption Framework (CAF), which breaks the journey into manageable phases.

1. Assess Phase: This initial phase involves discovering and evaluating the existing on-premises portfolio. The goal is to build a business case for migration and understand application dependencies.

• Discovery: Tools like AWS Application Discovery Service are used to collect server specifications, performance data, and network dependencies.
• Readiness Assessment: The AWS Cloud Readiness Assessment helps evaluate an organization's capabilities across six perspectives defined by the CAF: Business, People, Governance, Platform, Security, and Operations.

2. Mobilize Phase: In this phase, the organization builds its foundational AWS environment and operational readiness. This involves creating a "landing zone"—a secure, multi-account AWS environment—and refining the migration plan. The insights from the assess phase are used to select the right migration strategy for each application.

3. Migrate & Modernize Phase: This is the execution phase where applications and data are moved to AWS using one of the seven common migration strategies, often called the "7 Rs".

• Rehost (Lift and Shift): Moving applications without changes. This is the fastest approach and is often facilitated by AWS Application Migration Service (MGN), which uses continuous, block-level replication to minimize downtime.
• Replatform (Lift and Reshape): Making a few cloud optimizations without changing the core architecture. A common example is migrating an on-premises database to a managed service like Amazon Relational Database Service (RDS).
• Repurchase (Drop and Shop): Moving to a different product, often a Software-as-a-Service (SaaS) solution. For instance, moving from a self-hosted email server to a cloud-based email service.
• Refactor / Re-architect: Re-imagining how the application is architected and developed using cloud-native features. This strategy is driven by a strong business need for new features, scale, or performance and is the most complex.
• Relocate: Moving infrastructure to the cloud without purchasing new hardware or rewriting applications. This is specific to scenarios like moving a VMware estate to VMware Cloud on AWS.
• Retain: Keeping applications in the source environment because they are not ready for migration or are not a priority.
• Retire: Decommissioning applications that are no longer needed, which can lead to immediate cost savings.

Throughout this process, AWS Migration Hub provides a central location to track the progress of migrations across multiple AWS and partner tools.

Key Features and Limits

Cloud migration is a process supported by a suite of tools, each with its own features:

• AWS Application Migration Service (MGN):
  • Primary Tool for Rehosting: Simplifies and automates lift-and-shift migrations for physical, virtual, and other cloud-based servers.
  • Minimal Downtime: Uses continuous block-level replication and allows for non-disruptive testing before cutover.
  • Broad Compatibility: Supports a wide range of operating systems and applications.
• AWS Database Migration Service (DMS):
  • Homogeneous and Heterogeneous Migrations: Supports migrating between the same database engines (e.g., MySQL to Amazon Aurora) and different engines (e.g., Oracle to PostgreSQL).
  • Continuous Data Replication (CDC): Keeps the source database fully operational during the migration by replicating changes in near real-time.
  • Serverless Option: DMS Serverless automatically provisions and scales migration resources, so you only pay for the capacity you use.
• AWS Migration Hub:
  • Centralized Tracking: Provides a single dashboard to view the status of all server and application migrations.
  • Migration Strategy Recommendations: Can analyze discovered inventory and recommend one of the 7 Rs for each application.
  • Orchestration: Includes templates to automate and simplify complex migration workflows.

Common Use Cases

• Datacenter Evacuation: Moving all infrastructure out of a physical datacenter to reduce hardware costs, eliminate capital expenditures, and improve operational efficiency.
• Application Modernization: Migrating legacy applications to AWS to refactor them into a microservices architecture, leveraging services like AWS Lambda and Amazon ECS/EKS for greater agility and scalability.
• Database Freedom: Migrating from expensive, proprietary commercial databases (like Oracle or SQL Server) to open-source or cloud-native databases on AWS (like PostgreSQL, MySQL, or Amazon Aurora) to reduce licensing costs and avoid vendor lock-in.
• Cloud-Based Disaster Recovery (DR): Using migration tools like AWS MGN to establish a low-cost DR site in an AWS Region. Source servers can be continuously replicated to AWS, ready to be launched in the event of a disaster.
• Large-Scale Workload Migration: Moving hundreds or thousands of servers as part of a broad digital transformation initiative, often organized into migration "waves" planned and tracked with AWS Migration Hub.

Pricing Model

The cost of an AWS Cloud Migration is not a single fee but a combination of factors:

• Migration Tools: Many core AWS migration planning tools are free. For example, AWS Migration Hub and AWS Application Discovery Service are offered at no additional charge.
• Execution Services: Some migration execution services have a free tier followed by usage-based pricing. For instance, AWS Application Migration Service (MGN) is free for a 90-day period for each migrating server. AWS Database Migration Service (DMS) billing is based on the compute resources (Replication Instance) used and the volume of data replicated.
• Temporary Resources: During migration, you pay for staging resources, such as Amazon EBS snapshots and lightweight EC2 instances used as replication servers.
• Data Transfer: Data transfer into AWS from the internet is generally free. However, you will incur costs for data transfer out of AWS or between regions if your migration strategy requires it.
• Target AWS Resources: The primary cost is the ongoing expense of the AWS resources (e.g., EC2 instances, RDS databases, S3 storage) that your applications run on post-migration.

For detailed estimates, it is recommended to use the AWS Pricing Calculator.

Pros and Cons

Pros:

• Cost Savings: Reduces capital expenditure on hardware and lowers operational costs through pay-as-you-go pricing and managed services.
• Increased Agility and Innovation: Gain access to over 200 AWS services, enabling faster development cycles and the ability to build modern, scalable applications.
• Improved Security and Compliance: Leverage AWS's robust security posture and compliance certifications, offloading much of the responsibility for the security of the cloud to AWS.
• Enhanced Scalability and Performance: Dynamically scale resources up or down to meet demand, ensuring optimal performance and cost-efficiency.
• Global Reach and High Availability: Easily deploy applications across multiple AWS Regions to serve a global audience and build highly resilient architectures.

Cons:

• Complexity and Planning: Large-scale migrations are complex projects that require significant planning, discovery, and expertise to execute successfully.
• Potential for Downtime: While tools like MGN and DMS are designed to minimize disruption, poorly planned cutovers can still lead to application downtime.
• Skill Gap: Teams may lack the necessary cloud skills, requiring investment in training and a cultural shift towards a DevOps mindset.
• Cost Management Challenges: Without proper governance and cost optimization practices, cloud spending can become unexpectedly high.

Comparison with Alternatives

AWS Migration Tools vs. Manual Migration:

• Manual Migration: Involves manually provisioning AWS resources, installing software, and copying data. This approach offers maximum control but is slow, error-prone, and not scalable for large environments.
• AWS Migration Tools: Services like AWS MGN and DMS automate the most difficult parts of the migration process—data replication, server conversion, and cutover—making it faster, more reliable, and scalable.

Rehost (Lift-and-Shift) vs. Refactor (Cloud-Native):

• Rehost: The fastest path to the cloud. It allows organizations to exit a datacenter quickly and start realizing some cloud benefits immediately. However, it doesn't take full advantage of cloud-native capabilities.
• Refactor: The most transformative approach. It results in a highly optimized, scalable, and cost-efficient application but requires a significant upfront investment in time, skills, and resources. It is often a post-migration activity.

Exam Relevance

Cloud migration is a fundamental concept tested across multiple AWS certifications.

• AWS Certified Cloud Practitioner (CLF-C02): Requires a high-level understanding of the business benefits of cloud migration, the AWS Cloud Adoption Framework (CAF), and the general purpose of key migration services like AWS Migration Hub.
• AWS Certified Solutions Architect - Associate (SAA-C03): Expect scenario-based questions that require you to choose the appropriate migration strategy (e.g., rehost vs. replatform) and select the right AWS service (e.g., MGN for servers, DMS for databases) to meet specific business requirements with minimal downtime.
• Professional & Specialty Certifications: (e.g., Solutions Architect - Professional, Advanced Networking, Database) These exams test deep, hands-on knowledge of complex migration scenarios, including hybrid connectivity with AWS Direct Connect, multi-account governance, and intricate database conversion and cutover strategies.

Frequently Asked Questions

Q: What is the difference between rehosting and replatforming?

A: Rehosting (lift-and-shift) involves moving an application to the cloud with no changes to its architecture. Replatforming (lift-and-reshape) involves making some cloud optimizations, such as moving a self-managed database to a managed service like Amazon RDS, without fundamentally changing the application's core code.

Q: What is the AWS Cloud Adoption Framework (CAF)?

A: The AWS Cloud Adoption Framework (CAF) is a set of best practices and guidance from AWS to help organizations develop an effective and efficient plan for their cloud adoption journey. It organizes guidance into six perspectives: Business, People, Governance, Platform, Security, and Operations, to help identify and address gaps in skills and processes.

Q: How long does a cloud migration take?

A: The duration of a cloud migration varies significantly based on the size and complexity of the environment, the chosen migration strategies, and the organization's readiness. A small migration of a few servers might take weeks, while a large-scale datacenter evacuation can be a multi-year program executed in carefully planned waves.

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This article reflects AWS features and pricing as of 2026. AWS services evolve rapidly — always verify against the official AWS documentation before making production decisions.