Common ASP.NET Core Issues and Solutions

1. Dependency Injection (DI) Failures

Services fail to resolve, causing runtime errors such as System.InvalidOperationException: Unable to resolve service.

Root Causes:

• Missing service registration in Startup.cs or Program.cs.
• Incorrect service lifetime (Singleton, Scoped, Transient).
• Attempting to inject services into static classes.

Solution:

Ensure services are registered in Program.cs (ASP.NET Core 6+):

var builder = WebApplication.CreateBuilder(args);
builder.Services.AddScoped();
var app = builder.Build();

Verify constructor injection:

public class MyController : Controller
{
    private readonly IMyService _service;
    public MyController(IMyService service) {
        _service = service;
    }
}

For static classes, use a factory pattern instead of DI.

2. Middleware Misconfigurations

Middleware does not execute in the expected order, causing unexpected behavior.

Root Causes:

• Incorrect ordering of middleware in Program.cs.
• Middleware dependencies missing.
• Missing UseRouting and UseEndpoints in the request pipeline.

Solution:

Ensure middleware follows the correct order:

var app = builder.Build();
app.UseRouting();
app.UseAuthentication();
app.UseAuthorization();
app.UseEndpoints(endpoints => {
    endpoints.MapControllers();
});

Check that required services are added:

builder.Services.AddControllers();
builder.Services.AddAuthentication();
builder.Services.AddAuthorization();

3. Cross-Origin Resource Sharing (CORS) Issues

Requests from different origins fail with CORS-related errors.

Root Causes:

• Missing or misconfigured CORS policy.
• Middleware order issue.
• Incorrect AllowCredentials usage with wildcard origins.

Solution:

Enable CORS in Program.cs:

builder.Services.AddCors(options => {
    options.AddPolicy("MyCorsPolicy", policy => {
        policy.AllowAnyOrigin()
              .AllowAnyMethod()
              .AllowAnyHeader();
    });
});

Apply CORS in the middleware pipeline:

app.UseCors("MyCorsPolicy");

For authentication-based applications, specify allowed origins explicitly:

policy.WithOrigins("https://example.com").AllowCredentials();

4. Deployment and Configuration Failures

ASP.NET Core applications fail to deploy correctly or misbehave in production.

Root Causes:

• Incorrect environment settings.
• Missing environment variables.
• Platform-specific deployment issues.

Solution:

Set environment variables:

export ASPNETCORE_ENVIRONMENT=Production

Use configuration files:

appsettings.Production.json

For Azure App Service, ensure the correct runtime is set:

az webapp config set --name MyApp --resource-group MyGroup --linux-fx-version "DOTNETCORE|6.0"

5. Performance Bottlenecks

Applications experience slow response times and high resource usage.

Root Causes:

• Unoptimized database queries.
• Excessive middleware execution.
• Blocking synchronous calls in an asynchronous pipeline.

Solution:

Use asynchronous database queries:

await _dbContext.Users.ToListAsync();

Optimize middleware execution order:

app.UseResponseCaching();
app.UseRouting();

Avoid blocking synchronous calls:

await Task.Run(() => SomeLongRunningTask());

Best Practices for ASP.NET Core Optimization

• Use dependency injection properly and avoid injecting services into static classes.
• Ensure correct middleware order for authentication, authorization, and routing.
• Configure CORS correctly based on security needs.
• Use environment-based configurations to prevent deployment issues.
• Profile performance and optimize slow database queries.

Conclusion

By troubleshooting dependency injection failures, middleware misconfigurations, CORS issues, deployment problems, and performance bottlenecks, developers can build high-performance ASP.NET Core applications. Implementing best practices ensures a robust, scalable, and maintainable backend architecture.

FAQs

1. Why is dependency injection failing in ASP.NET Core?

Ensure services are registered in Program.cs and check constructor injection usage.

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

Define a proper CORS policy and apply it before authentication middleware.

3. How do I optimize ASP.NET Core performance?

Use async methods, minimize middleware execution, and optimize database queries.

4. Why does my ASP.NET Core app fail to deploy?

Check environment variables, configuration files, and ensure the correct .NET runtime is installed.

5. How do I debug middleware execution order issues?

Enable logging and verify middleware order in Program.cs to ensure correct execution flow.