.NET: Preparing an Existing Application for .NET 10

Introduction

Upgrading a mature .NET application requires more than changing the target framework in a project file. Applications may depend on outdated packages, obsolete APIs, environment-specific configuration, and behaviors that are not fully covered by tests.

Preparing early for a framework upgrade reduces uncertainty and makes it easier to separate application problems from changes introduced by the new runtime.

1. Establish a baseline

Before changing the application, record the current state:

• Target framework and SDK version.
• Direct and transitive NuGet dependencies.
• Existing warnings and build failures.
• Test results and code coverage for critical workflows.
• Startup time, memory usage, and important endpoint latencies.
• Deployment and rollback procedures.

A baseline helps identify whether a regression is new or already existed. Performance measurements are especially important: without them, it is difficult to prove that an upgrade improved or harmed the application.

2. Inspect the project and SDK

A project might currently target an earlier framework:

<PropertyGroup>
  <TargetFramework>net8.0</TargetFramework>
  <Nullable>enable</Nullable>
  <ImplicitUsings>enable</ImplicitUsings>
</PropertyGroup>

The target can be changed to net10.0 when the application is ready and the required SDK and dependencies are available:

<PropertyGroup>
  <TargetFramework>net10.0</TargetFramework>
  <Nullable>enable</Nullable>
  <ImplicitUsings>enable</ImplicitUsings>
</PropertyGroup>

This is only one step in the upgrade. Confirm the SDK version used by local development and CI, update any relevant global.json settings, and review hosting and deployment requirements.

3. Audit NuGet dependencies

Framework upgrades can expose compatibility problems in packages, analyzers, code generators, and build tools.

Start by listing outdated packages:

dotnet list package --outdated

Then inspect vulnerabilities:

dotnet list package --vulnerable --include-transitive

The exact command syntax may vary with the SDK and tooling version. Review each result rather than upgrading every dependency blindly.

For important packages, check supported target frameworks, release notes, breaking changes, and compatibility with the new runtime. Pay particular attention to database providers, authentication packages, serialization libraries, and observability integrations.

4. Use automated upgrade analysis

Microsoft’s upgrade tooling can help identify APIs and project configuration that need attention. Automated analysis is a starting point, not a guarantee that the application will behave correctly after migration.

Review each recommendation in the context of the codebase. A suggested replacement may require changes to tests, configuration, or architecture rather than a simple text substitution.

Keep changes small enough that build or test failures can be traced to a specific upgrade step.

5. Strengthen integration tests

A framework upgrade can affect routing, serialization, dependency injection, authentication, hosting, and database integration.

Prioritize tests for:

• Authentication and authorization.
• Request validation and error responses.
• Database migrations and transactions.
• Background services and application shutdown.
• External API calls and timeout handling.
• Configuration loading and startup validation.

Unit tests remain valuable, but integration tests are especially important for confirming that the application works with its actual framework and infrastructure.

6. Test deployment and rollback

A successful local build does not prove that production deployment will work. Check container images, runtime availability, health checks, environment variables, TLS configuration, and monitoring agents.

Deploy to a representative staging environment before production. Define success criteria and a rollback procedure in advance, especially for applications that also change database schemas.

Conclusion

Preparing for .NET 10 is an opportunity to improve dependency health, test coverage, deployment confidence, and operational visibility. Establish a baseline, audit packages, analyze breaking changes, and validate the application in a realistic environment before rolling out the upgrade.