Laravel Kernel & Middleware Notes

1. What is the Laravel Kernel?

The Kernel in Laravel is like the “traffic controller” of the application. It decides:

• Which requests should pass through security checks.
• Which logic should run before a controller handles a request.
• How responses go back to the user.

2. Types of Kernel in Laravel

• HTTP Kernel: Handles browser/API requests. File: app/Http/Kernel.php
• Console Kernel: Handles command-line (artisan) requests. File: app/Console/Kernel.php

3. HTTP Kernel Responsibilities

• Manages middleware for web and API routes.
• Applies global rules to all requests (like trimming inputs, trusting proxies).
• Applies route-specific middleware (like auth or admin).
• Handles sessions, CSRF protection, cookies, and response adjustments.

protected $middlewareGroups = [
    'web' => [
        \App\Http\Middleware\EncryptCookies::class,
        \Illuminate\Session\Middleware\StartSession::class,
        \Illuminate\View\Middleware\ShareErrorsFromSession::class,
        \App\Http\Middleware\VerifyCsrfToken::class,
        \Illuminate\Routing\Middleware\SubstituteBindings::class,
    ],
    'api' => [
        'throttle:api',
        \Illuminate\Routing\Middleware\SubstituteBindings::class,
    ],
];

protected $routeMiddleware = [
    'auth' => \App\Http\Middleware\Authenticate::class,
    'admin' => \App\Http\Middleware\AdminMiddleware::class,
];
    

4. Why Kernel Errors Happen

If a route references a middleware like admin but it is not registered in the Kernel, Laravel cannot find it and throws:

Target class [admin] does not exist.

Solution: either register the middleware in $routeMiddleware or remove it from the route.

5. Middleware & Security

• Middleware acts like rules or gates that a request must pass through.
• Examples of middleware:
  • auth: Only logged-in users can access certain pages.
  • admin: Only users with the admin role can access sensitive pages.
  • throttle: Limits how many requests a user can make in a short time.

6. Summary

• Laravel Kernel is the main controller of requests and responses.
• Middleware are rules applied by the Kernel to secure and manage traffic.
• Always register your custom middleware (like admin) in the Kernel.
• Think of Kernel as a building security system and middleware as the rules for different rooms.