How to Use .NET Upgrade Assistant for Migrating Legacy .NET Projects

This article provides introduction of using .NET Upgrade Assistant for migrating .NET Projects on previous version of .NET that are out of support to latest .NET Core version.

.NET Upgrade Assistant ASP.NET Core Software Modernization

How to Use .NET Upgrade Assistant for Migrating Legacy .NET Projects

Tuesday, May 13, 2025
Tuesday, May 13, 2025

This article provides introduction of using .NET Upgrade Assistant for migrating .NET Projects on previous version of .NET that are out of support to latest .NET Core version.

The .NET ecosystem has evolved significantly, with .NET Core emerging as the future-proof platform for modern applications. However, migrating legacy .NET Framework projects can be daunting due to compatibility issues, architectural differences, and the sheer scale of enterprise codebases. Enter the .NET Upgrade Assistant, a tool designed by Microsoft to streamline this transition. This 4000-word guide explores how to leverage this tool effectively, covering installation, migration strategies, best practices, and real-world insights.

Understanding the .NET Upgrade Assistant

The .NET Upgrade Assistant is an open-source tool that automates the migration of legacy .NET Framework, .NET Core, or Xamarin projects to modern .NET versions (e.g., .NET 6, 7, or 8). It analyzes codebases, identifies compatibility issues, and applies automated fixes, reducing manual effort and errors.

Key Features

Guided Workflow: Step-by-step prompts for upgrading projects.
Multi-Project Support: Handles ASP.NET, WPF, WinForms, Class Libraries, and Azure Functions.
Incremental Migration: Allows partial upgrades while maintaining legacy functionality.
Dependency Analysis: Flags outdated NuGet packages and unsupported APIs.

Supported Upgrade Paths

.NET Framework → .NET 6/7/8
.NET Core 3.1 → .NET 6+
Xamarin.Forms → .NET MAUI
UWP → WinUI 3
Azure Functions v1-v3 → v4 (isolated)

Installing the .NET Upgrade Assistant

The tool is available in two forms:

Option 1: Visual Studio Extension

Open Visual Studio (2022 recommended).
Navigate to Extensions > Manage Extensions.
Search for ".NET Upgrade Assistant" and install.
Restart Visual Studio.

Option 2: CLI Tool

dotnet tool install -g upgrade-assistant

Validation

Visual Studio: Right-click a project → Check for an Upgrade menu item.
CLI: Run upgrade-assistant to verify installation

Migration Strategies

Strategy 1: Incremental Migration (Recommended)

The Strangler Fig Pattern is ideal for large applications. It uses a reverse proxy (e.g., YARP) to route requests between legacy and modern systems, enabling gradual migration. Steps:

Side-by-Side Setup: Create a new ASP.NET Core project alongside the legacy app.
Proxy Configuration: Use YARP to route specific endpoints to the new project.
Iterative Refactoring: Migrate components incrementally (e.g., one controller at a time).

Strategy 2: Full Rewrite

Suitable for smaller projects or those requiring architectural changes (e.g., transitioning from Web Forms to Blazor).

Strategy 3: Hybrid Approach

Combine automated upgrades with manual fixes for critical components.

Step-by-Step Migration Process

Step 1: Pre-Migration Preparation

Backup Code: Ensure a rollback plan exists.
Audit Dependencies: Use the .NET Portability Analyzer to identify incompatible APIs and NuGet packages.
Update Legacy Code: Resolve deprecated patterns (e.g., Web.config → appsettings.json).

Step 2: Running the Upgrade Assistant

In Visual Studio:

Right-click the project → Upgrade.
Select Side-by-Side Incremental (for large apps) or In-Place Upgrade (for smaller projects).
Choose the target framework (e.g., .NET 8).
Review automated changes and apply fixes.

Via CLI:

upgrade-assistant upgrade <ProjectPath>

The tool interactively guides you through:

Updating project files (e.g., .csproj).
Adjusting NuGet dependencies.
Applying code fixes for breaking changes

Step 3: Post-Migration Tasks

Manual Refactoring:
- Replace unsupported APIs (e.g., System.Web → Microsoft.AspNetCore).
- Migrate authentication (WS-Security → JWT/OAuth 2.0).
Testing:
- Unit tests (xUnit/NUnit).
- Integration tests (e.g., API endpoints).
- Performance benchmarks (compare latency with legacy systems).
Deployment:
- Use CI/CD pipelines (Azure DevOps, GitHub Actions).
- Monitor with Application Insights

Common Challenges and Solutions

Challenge	Solution
Unsupported APIs	Use shim libraries or rewrite logic (e.g., Remoting → gRPC).
Legacy NuGet Packages	Find alternatives on NuGet.org or contribute to open-source forks.
Web Forms Compatibility	Rewrite UI with Blazor or Razor Pages.
Enterprise-Scale Codebases	Break into microservices; use incremental migration.

Best Practices

Start Small: Test the tool on non-critical projects first.
Leverage Automation: Use the CLI tool in CI/CD pipelines for batch upgrades.
Monitor Performance: Track metrics like memory usage and request latency post-migration.
Collaborate with Teams: Involve QA early to validate incremental changes.

Limitations and Workarounds

No Architectural Refactoring: The tool focuses on code-level fixes, not system redesign.
Limited Web Forms Support: Requires manual UI rewrites.
Complex Dependencies: Enterprise apps may need custom solutions for proprietary libraries.

Tools and Resources

YARP: For incremental routing.
.NET Portability Analyzer: Dependency auditing.
Application Insights: Post-migration monitoring.
Microsoft Learn: Official documentation and tutorials.

Conclusion

The .NET Upgrade Assistant is a powerful ally for modernizing legacy systems, but success hinges on strategic planning. By combining automated upgrades with manual refinements and leveraging patterns like Strangler Fig, teams can achieve seamless transitions to .NET Core. While challenges like unsupported APIs persist, the tool’s guided workflow and community support make it indispensable for enterprises aiming to stay competitive.

Not sure how to approach your legacy WCF project? Contact us for a free 30 hour consultation.

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