AZ-305 Migration Strategy: Rehost, Refactor, or Rearchitect Without Falling for the Trap

For AZ-305 migration questions, do not pick rehost, refactor, or rearchitect because one sounds more modern. Pick the least disruptive path that still satisfies the business and technical constraints. Rehost is the fast like-for-like move when the workload is stable and does not need near-term modernization. Refactor is the code-level improvement path when technical debt, SDK changes, or cloud optimization justify development work. Rearchitect is the bigger design change when the current architecture blocks scale, agility, service boundaries, or cloud-native operations.

Microsoft says the English AZ-305 exam was updated on April 17, 2026, and Design infrastructure solutions is weighted 30-35% (AZ-305 exam page). The current study guide explicitly includes migration evaluation with the Microsoft Cloud Adoption Framework, evaluating on-premises servers, data, and applications, and recommending IaaS and PaaS migration paths (AZ-305 study guide).

Compact Decision Shortcut

• Rehost when the workload is stable, Azure-compatible, time constrained, and the business wants minimal disruption with no immediate modernization requirement (Cloud Adoption Framework migration strategies).
• Replatform when the app can move to a managed platform with minimal code change, such as a web app moving toward App Service or containers moving toward a managed container platform.
• Refactor when code changes are justified by technical debt, performance, observability, SDK updates, or cloud optimization goals.
• Rearchitect when the architecture itself is the blocker: monolith decomposition, independently scaled components, event-driven patterns, microservices, or long-term agility.
• Retain, retire, replace, or rebuild when moving the workload is not the right answer yet. AZ-305 may punish migration-by-default thinking.

One Mobile-Readable Decision Flow

The trap is treating this as a maturity ladder. It is not. A correct answer can be rehost if the scenario rewards speed, risk control, and compatibility. A correct answer can be rearchitect if the existing design cannot meet the target scale or operating model. The exam clue is the constraint, not the prestige of the option.

What The Cloud Adoption Framework Adds

The Cloud Adoption Framework is not just vocabulary. Its migration strategy guidance starts from workload inventory and business drivers, then maps each workload to an action such as retire, retain, rehost, replatform, refactor, rearchitect, rebuild, or replace. Microsoft also warns that modernization during migration adds complexity and should be justified by skills, time, compatibility needs, and business alignment (Cloud Adoption Framework migration strategies).

For AZ-305, translate that into three exam habits:

• Ask whether the workload should move at all before choosing a target service.
• Separate migration path from hosting target. A VM target does not automatically mean the best strategy was chosen.
• Match modernization depth to the stated constraint. Do not invent a rewrite when the prompt only asks for datacenter exit speed.

Scenario: The Payroll Portal Deadline

A company has a payroll portal running on three Windows Server VMs in VMware. The app uses IIS, a scheduled Windows service, a SQL Server database, and a vendor DLL. The datacenter lease expires in six months. The business requirement is to keep payroll stable through year-end, reduce datacenter dependency, and avoid large code changes before the next compliance audit. The architecture team also wants a future path to managed web hosting and better release automation.

First pass: this is not a rearchitect-first scenario. The deadline, vendor dependency, and audit risk make a large redesign hard to justify. Rehost the app servers to Azure VMs if Azure Migrate assessment confirms readiness, sizing, cost, and dependencies. Azure Migrate helps discover, assess, plan, and execute migrations across servers, databases, and web applications; its planning phase checks Azure readiness, right-sizing, cost estimation, and dependency analysis (Azure Migrate overview).

Second pass: do not stop thinking after rehost. The future managed-hosting goal may become a replatform or refactor phase. Azure App Service can host web apps and APIs as a fully managed web platform, and Microsoft documents migration tooling for assessing and moving supported web apps to App Service (App Service migration resources, Container Apps comparison). If the vendor DLL, Windows service, or registry/COM dependency blocks normal App Service hosting, that is evidence against a rushed PaaS move, not evidence that PaaS is bad.

Third pass: rearchitect only when the scenario changes. If payroll must support independent scaling for calculation, approval, notification, and reporting services, or the monolith prevents release speed and resilience targets, a phased rearchitect path can become defensible. Microsoft modernization guidance describes rearchitecting as redesigning architecture with cloud-native patterns such as microservices, serverless, or event-driven design when current architecture limits growth or cloud optimization (Plan cloud modernization).

Exam-ready answer: rehost now, plan a later replatform or refactor for the web tier if assessment proves it is compatible, and reserve rearchitecting for a later phase with explicit scalability or service-boundary requirements.

Service Boundaries That Change The Answer

Azure Migrate is the portfolio and execution hub, not a magic label that makes every target correct. It supports discovery, assessment, business cases, migration planning, and migration or modernization for servers, databases, web apps, virtual desktops, and offline data. It can assess IaaS and PaaS targets, but the architect still has to choose the treatment that fits the workload (Azure Migrate overview).

Use Azure VMs when OS control, installed agents, legacy software, custom configuration, or lift-and-shift compatibility are real constraints. Microsoft describes IaaS as closest to a traditional on-premises environment: Azure manages the infrastructure, while you manage the VMs (Choose an Azure compute service).

Use App Service when the workload is a web app or API that can fit a managed web platform. Use Container Apps when containerized microservices, jobs, revisions, traffic splitting, event-driven scale, or scale to zero matter without direct Kubernetes API control. Use AKS when Kubernetes API/control-plane access is an explicit requirement (Container Apps comparison). Use Functions when the unit of work is event-driven code rather than a full migrated server app. If the scenario is about preserving VMware operations and platform compatibility, Azure VMware Solution is adjacent; Microsoft describes it as private clouds with VMware vSphere clusters on dedicated Azure bare-metal infrastructure, not as the default target for every VM migration (Azure VMware Solution overview).

For adjacent compute placement decisions, the AZ-305 compute hosting guide is the better next read. If the migration prompt turns into private connectivity, datacenter reachability, or DNS, use the AZ-305 hybrid network connectivity guide.

What Wrong Answers Reveal

• Choosing rearchitect for the payroll deadline means you may be over-valuing modernization and under-valuing risk and timing.
• Choosing rehost for a fragile, unscalable monolith means you may be carrying forward the exact failure mode the business needs fixed.
• Choosing App Service because the workload has IIS means you may have ignored installed dependencies or unsupported configuration.
• Choosing AKS because containers are mentioned means you may have missed that Container Apps can cover serverless container patterns without Kubernetes API control.
• Choosing Azure VMware Solution for every VMware source means you may be preserving the platform when the requirement only asked for Azure migration.
• Migrating every workload means you may have missed retain, retire, replace, or rebuild as valid business decisions.

CramHQ practice should turn each miss into one label: timing, compatibility, operating model, code debt, architecture boundary, or target-service fit. That is more useful than rereading every migration page.

How To Study This For AZ-305

Practice by changing one requirement at a time:

• Replace "six-month datacenter deadline" with "must support 3x traffic and independent release cycles." Does rearchitect become stronger?
• Add "vendor agent must be installed on the OS." Does rehost to VMs become defensible?
• Remove the vendor dependency and add "reduce patching and hosting operations." Does replatform to App Service become stronger?
• Add "queue-triggered document processing." Does Functions or Container Apps jobs enter the design?
• Add "keep VMware tooling and vSphere operations with minimal retraining." Does Azure VMware Solution become worth evaluating?

When you are ready to see whether this decision pattern is actually costing you points, take the AZ-305 assessment. CramHQ is independent exam-preparation software, not a Microsoft product and not a pass guarantee. Its value here is the learning loop: identify which migration boundary you missed, repair it with focused lessons and practice, then retest nearby scenarios instead of studying the whole infrastructure domain again.

Quick Recap

Rehost for stable, compatible workloads when speed and risk control dominate. Replatform when managed hosting reduces operations with limited code change. Refactor when code-level changes are justified. Rearchitect when the design itself blocks scale, agility, or cloud-native operation. On AZ-305, the best answer is the migration depth that satisfies the stated business and technical constraints without inventing a rewrite or hiding a real compatibility blocker.