How to Migrate Legacy Applications Using GitHub Copilot

Migrating legacy applications to modern platforms is one of the most challenging tasks in software development. Legacy systems often contain years of business logic, outdated frameworks, and dependencies that are no longer supported. At the same time, businesses need these applications to remain reliable and secure while benefiting from modern practices.

This is where GitHub Copilot can become a powerful ally. By acting as your AI pair programmer, Copilot can help accelerate repetitive refactoring tasks, suggest modern equivalents for deprecated code, and provide scaffolding for newer frameworks. While it won’t completely automate a migration, it can dramatically reduce the effort and improve developer productivity.

Why Modernize Legacy Applications?

Legacy systems often:

Depend on outdated frameworks or runtimes (e.g., Python 2, .NET Framework, Java 7).
Lack automated tests, making changes risky.
Contain “tribal knowledge” hidden in decades-old code.
Are hard to scale, integrate, and secure.

Modernizing brings benefits like:

Better maintainability.
Improved security and compliance.
Easier integration with modern cloud services.
Enhanced developer productivity.

Step 1: Assess and Plan

Before writing a single line of new code, you need a roadmap:

Identify the current tech stack (language, framework, libraries).
Define the target stack (e.g., upgrading Python 2 to Python 3.12, or moving .NET Framework to .NET 8).
Audit dependencies – flag libraries that are deprecated.
Testing strategy – add unit and integration tests to capture current behavior.

Step 2: Set Up GitHub Copilot

To make Copilot part of your migration toolkit:

Install Copilot in Visual Studio Code, JetBrains IDEs, or Visual Studio.
Pair Copilot with GitHub Copilot Chat to ask migration-specific questions (e.g., “Rewrite this Python 2 function for Python 3 compatibility”).
Configure Copilot to work on smaller, focused files where it can provide accurate suggestions.

Step 3: Use Copilot for Incremental Refactoring

Instead of rewriting everything at once, migrate piece by piece:

Upgrade syntax: Copilot can automatically suggest modern equivalents for old code constructs.
Example: Converting Python 2 print statements to Python 3 print() functions.
Refactor APIs: When APIs change (e.g., old database drivers to new ORM methods), Copilot can suggest the updated calls.
Generate boilerplate: For new services or modules, Copilot can scaffold class definitions, REST endpoints, or test cases.

Step 4: Bridge Old and New

During migration, you may run both old and new code together:

Use wrappers or adapters so new modules can talk to legacy components.
Ask Copilot to draft adapters between old APIs and modern equivalents.

Step 5: Validate with Tests

Testing ensures you haven’t broken existing functionality:

Copilot can help write unit tests for legacy code (even before refactoring).
Use tests as a safety net while you modernize modules incrementally.

Step 6: Continuous Integration & Deployment

Set up CI pipelines to run tests automatically on each migration step.
Deploy modernized modules alongside legacy ones until the migration is complete.

Example: Python 2 to Python 3 Migration with Copilot

Imagine you have this Python 2 function:

def greet(name):
    print "Hello, " + name

With Copilot’s assistance, you can quickly modernize it to:

def greet(name: str) -> None:
    print("Hello, " + name)

Copilot also suggests adding type hints, improving readability, and making the code future-proof.

Best Practices for Using Copilot in Migrations

Don’t fully trust suggestions – always review Copilot’s code for accuracy.
Work in small increments – migrate file by file or module by module.
Leverage Copilot Chat – ask it why it’s suggesting changes.
Keep humans in control – AI helps, but architects and developers make the final calls.

Migrating legacy applications is never easy, but with a structured plan and the right tools, it becomes manageable. GitHub Copilot won’t replace your expertise, but it acts like a skilled assistant, helping you modernize faster, reduce repetitive work, and focus on the architecture and strategy that really matter.

If you’re facing a legacy migration, start small, bring Copilot into your workflow, and let AI accelerate your journey to modern code.