Common ASP.NET Core Issues and Solutions

1. Dependency Injection Failures

ASP.NET Core applications may throw errors due to incorrect dependency injection (DI) configurations.

Root Causes:

• Services not registered in the DI container.
• Incorrect service lifetimes (Scoped, Transient, Singleton).
• Misconfigured constructor injection.

Solution:

Ensure services are registered in Program.cs:

builder.Services.AddScoped<IMyService, MyService>();

Verify correct constructor injection:

public class MyController(IMyService myService) {    _myService = myService ?? throw new ArgumentNullException(nameof(myService));}

Use the correct lifetime scope:

builder.Services.AddSingleton<IMySingletonService, MySingletonService>();

2. Routing Not Working

Routes may not resolve correctly, resulting in 404 errors.

Root Causes:

• Incorrect route templates.
• Conflicts between attribute and conventional routing.
• Endpoints not correctly mapped.

Solution:

Ensure controllers use correct attribute routing:

[Route("api/[controller]")][ApiController]public class MyController : ControllerBase { }

Verify endpoint mapping in Program.cs:

app.UseRouting();app.UseEndpoints(endpoints => {    endpoints.MapControllers();});

Check case sensitivity in route definitions.

3. CORS Policy Not Applied

Cross-Origin Resource Sharing (CORS) errors occur when API requests from different domains are blocked.

Root Causes:

• CORS policy not registered in the pipeline.
• Incorrect CORS configuration.
• Using WithOrigins without allowing all necessary headers and methods.

Solution:

Register CORS in Program.cs:

builder.Services.AddCors(options => {    options.AddPolicy("AllowAll", builder =>        builder.AllowAnyOrigin()               .AllowAnyMethod()               .AllowAnyHeader());});app.UseCors("AllowAll");

Ensure middleware order is correct:

app.UseRouting();app.UseCors("AllowAll");app.UseAuthorization();app.MapControllers();

4. Slow API Performance

ASP.NET Core APIs may suffer from slow response times.

Root Causes:

• Unoptimized database queries.
• Excessive logging or middleware overhead.
• Blocking operations in asynchronous code.

Solution:

Optimize database queries using AsNoTracking():

var users = _context.Users.AsNoTracking().ToList();

Reduce logging verbosity in appsettings.json:

"Logging": {    "LogLevel": {        "Default": "Warning"    }}

Use asynchronous methods properly:

await Task.Delay(1000);

5. Deployment Fails on IIS or Azure

ASP.NET Core applications may fail to deploy properly due to environment misconfigurations.

Root Causes:

• Incorrect hosting model (InProcess vs. OutOfProcess).
• Missing environment variables.
• File permission issues on the server.

Solution:

Ensure correct hosting model in web.config:

<aspNetCore processPath="dotnet" arguments="MyApp.dll" hostingModel="InProcess"/>

Set environment variables before deployment:

export ASPNETCORE_ENVIRONMENT=Production

For Azure, configure app settings in the portal.

Best Practices for ASP.NET Core Development

• Use dependency injection properly to manage service lifetimes.
• Ensure correct middleware ordering in Program.cs.
• Optimize database queries to prevent slow API responses.
• Use structured logging and monitor performance.
• Test deployments locally before pushing to production.

Conclusion

By troubleshooting dependency injection failures, routing issues, CORS misconfigurations, performance bottlenecks, and deployment challenges, developers can efficiently build and maintain ASP.NET Core applications. Implementing best practices ensures a scalable and performant back-end system.

FAQs

1. Why is my service not resolving in ASP.NET Core?

Ensure the service is registered in the DI container and use correct constructor injection.

2. How do I fix routing errors in ASP.NET Core?

Verify route templates, ensure endpoints are mapped correctly, and check for conflicts between attribute and conventional routing.

3. Why is my CORS policy not working?

Ensure CORS is properly registered, configured correctly, and applied in the middleware pipeline.

4. How can I improve ASP.NET Core API performance?

Optimize database queries, reduce unnecessary logging, and use asynchronous programming effectively.

5. Why is my ASP.NET Core app not working after deployment?

Check hosting model settings, set correct environment variables, and verify file permissions on the server.