How to Build a Secure Multi-Language Online Compiler Using Angular + .NET Core + Docker

Online compilers are no longer just a learning tool — they are powering coding interviews, developer onboarding, and cloud-based IDEs. If you want to build one that supports multiple languages like , C, Java and C#, you need to think about:

• Developer experience (the coding feel)
• Execution safety
• Performance & scalability In this guide, I’ll show how we built Igknight, a modern multi-language online compiler, using: Angular + Monaco Editor + .NET Core + Docker Sandbox Execution

Frontend: Angular + Monaco = VS Code in the Browser

For enterprise-quality development, Angular gives consistency and long-term maintainability.

To create a real coding environment, we integrate Monaco (the engine behind VS Code):
✔ Syntax highlighting for dozens of languages
✔ Auto-complete + IntelliSense-like suggestions
✔ Keyboard shortcuts devs already know
✔ Themeing + fully customizable UI
We also apply custom CSS to match Igknight platform styling so users feel like they're inside a real IDE. If you want to explore the underlying frontend technologies, you can learn more about styling with CSS and building scalable frontends with TypeScript. We also ensure valid HTML structure for the editor components.
🛡 Client-Side Code Validation
Before sending to the server, we check:

• Language selection vs code format
• Code length limits
• Basic malicious pattern filtering
• Required structure (e.g., main() for Java/C) This saves backend resources and improves speed

Backend: .NET Core Handles Execution Logic

The backend uses .NET Core to serve the API and manage the secure execution workflow. The .NET platform is an excellent choice for its high performance and robust security features, which are critical for this task.
The backend is responsible for:

1. Receiving code + selected language
2. Creating a temporary file securely
3. Selecting the correct Docker runner image
4. Executing with:
5. CPU + memory usage limits
6. No network access
7. Execution timeout
8. Capturing output + errors
9. Destroying container → no persistent files Multi-Language Support with Docker We build lightweight, language-specific Docker images. This container-per-execution model is the key to both security and multi-language support. Language,Execution Strategy Python, Direct .py execution C,GCC compile → isolated binary run Java, javac → java run C#, dotnet compile & execute

For our C# language support, we utilize the official tools. If you are interested in exploring the language used for our high-performance backend, you can dive into the official C# language documentation.
Each executes in a fresh sandbox for ultimate security.
⚙ Execution Flow Example (.NET Core)
var file = CreateTempFile(request.Code, request.Language);
var image = MapToDockerImage(request.Language);
var result = ExecuteDocker(image, file, new SecureOptions
{
TimeoutSeconds = 5,
MemoryLimitMb = 256
});

Cleanup(file);
return result;

We also loop through user test cases and return detailed feedback.
🛡 Security Considerations
Security is paramount when running untrusted user code. Docker ensures complete filesystem isolation 🔒, acting as a crucial security layer.

Threat,Solution
Infinite loops,Global timeout limit
Excess memory,RAM limits (Docker)
System access attempt,Container with no host permissions
Malware persistence,Destroy container after each run
Sensitive data exposure,Output sanitization

📈 Why This Architecture Scales

• Stateless API = easy load balancing
• Containers pull pre-built language images
• High burst execution capacity
• Efficient cleanup → no leftover resource usage We can handle 1000s of code executions per minute. *🎯 Experience the Compiler Live on Igknight * Want to try the full environment with a coding challenge?

The same compiler architecture described above powers our interactive tools: 👉 Try a C# Coding Challenge on Igknight
Perfect for:

• Backend developers
• Students learning .NET
• Coding interview preparation
• Quick experiments without IDE setup

Thanks from the Igknight Team!