diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 65fcfee..ed32dbf 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -10,12 +10,9 @@ jobs:
       max-parallel: 10
       fail-fast: false
       matrix:
-        php: ['7.3', '7.4', '8.0', '8.1']
-        sf_version: ['4.4.*', '5.0.*', '5.2.*', '5.4.*', '6.0.*']
+        php: ['7.4', '8.0', '8.1']
+        sf_version: ['5.2.*', '5.4.*', '6.0.*']
         exclude:
-          - php: 7.3
-            sf_version: 6.0.*
-            
           - php: 7.4
             sf_version: 6.0.*
 
@@ -48,7 +45,7 @@ jobs:
       - name: Set up PHP
         uses: shivammathur/setup-php@2.7.0
         with:
-          php-version: 7.3
+          php-version: 7.4
           coverage: pcov
 
       - name: Checkout code
@@ -59,5 +56,5 @@ jobs:
 
       - name: Run tests
         env:
-          PHP_VERSION: 7.3
+          PHP_VERSION: 7.4
         run: ./vendor/bin/phpunit -v --coverage-text
diff --git a/.gitignore b/.gitignore
index 1928cc9..1a2bb4b 100644
--- a/.gitignore
+++ b/.gitignore
@@ -2,3 +2,4 @@
 /composer.phar
 /composer.lock
 .phpunit.result.cache
+/var/
diff --git a/README.md b/README.md
index 4f0351f..6ef38d5 100644
--- a/README.md
+++ b/README.md
@@ -1,4 +1,4 @@
-This package configures Symfony to run on AWS Lambda using [Bref](https://bref.sh/).
+Run Symfony on AWS Lambda using the [Bref](https://bref.sh/) runtime.
 
 [![Build Status](https://github.com/brefphp/symfony-bridge/workflows/Tests/badge.svg)](https://github.com/brefphp/symfony-bridge/actions)
 [![Latest Version](https://img.shields.io/packagist/v/bref/symfony-bridge?style=flat-square)](https://packagist.org/packages/bref/symfony-bridge)
@@ -95,3 +95,69 @@ class Kernel extends BrefKernel
 +    }
 }
 ```
+
+## Handling requests in a kept-alive process without FPM
+
+> Note: this is an advanced topic. Don't bother with this unless you know what you are doing.
+
+To handle HTTP requests via the Symfony Kernel, without using PHP-FPM, by keeping the process alive:
+
+```diff
+# serverless.yml
+
+functions:
+    app:
+-        handler: public/index.php
++        handler: App\Kernel
+        layers:
+            # Switch from PHP-FPM to the "function" runtime:
+-            - ${bref:layer.php-80-fpm}
++            - ${bref:layer.php-80}
+        environment:
+            # The Symfony process will restart every 100 requests
+            BREF_LOOP_MAX: 100
+```
+
+The `App\Kernel` will be retrieved via Symfony Runtime from `public/index.php`. If you don't have a `public/index.php`, read the next sections.
+
+## Class handlers
+
+To handle other events (e.g. [SQS messages with Symfony Messenger](https://github.com/brefphp/symfony-messenger)) via a class name:
+
+```diff
+# serverless.yml
+
+functions:
+    sqsHandler:
+-        handler: bin/consumer.php
++        handler: App\Service\MyService
+        layers:
+            - ${bref:layer.php-80}
+```
+
+The service will be retrieved via Symfony Runtime from the Symfony Kernel returned by `public/index.php`.
+
+> Note: the service must be configured as **public** (`public: true`) in the Symfony configuration.
+
+### Custom bootstrap file
+
+If you do not have a `public/index.php` file, you can create a file that returns the kernel (or any PSR-11 container):
+
+```php
+<?php
+
+require_once dirname(__DIR__).'/vendor/autoload_runtime.php';
+
+return function (array $context) {
+    return new App\Kernel($context['APP_ENV'], (bool) $context['APP_DEBUG']);
+};
+```
+
+And configure it in `serverless.yml`:
+
+```diff
+# serverless.yml
+functions:
+    sqsHandler:
+        handler: kernel.php:App\Service\MyService
+```
diff --git a/composer.json b/composer.json
index 18bc730..0221a92 100644
--- a/composer.json
+++ b/composer.json
@@ -11,7 +11,10 @@
     "autoload": {
         "psr-4": {
             "Bref\\SymfonyBridge\\": "src/"
-        }
+        },
+        "files": [
+            "src/bootstrap.php"
+        ]
     },
     "autoload-dev": {
         "psr-4": {
@@ -19,17 +22,21 @@
         }
     },
     "require": {
-        "php": ">=7.3",
-        "bref/bref": "^1.0",
-        "symfony/filesystem": "^4.4|^5.0|^6.0",
-        "symfony/http-kernel": "^4.4|^5.0|^6.0"
+        "php": ">=7.4",
+        "bref/bref": "^1.2",
+        "symfony/filesystem": "^5.2|^6.0",
+        "symfony/http-kernel": "^5.2|^6.0",
+        "symfony/psr-http-message-bridge": "^2.1",
+        "symfony/runtime": "^5.2|^6.0"
     },
     "require-dev": {
         "mnapoli/hard-mode": "^0.3.0",
-        "phpunit/phpunit": "^8.0",
-        "symfony/config": "^4.4|^5.0|^6.0",
-        "symfony/dependency-injection": "^4.4|^5.0|^6.0",
-        "symfony/process": "^4.4|^5.0|^6.0"
+        "phpstan/phpstan": "^1.3",
+        "phpunit/phpunit": "^8.5.22",
+        "symfony/config": "^5.2|^6.0",
+        "symfony/dependency-injection": "^5.2|^6.0",
+        "symfony/framework-bundle": "^5.2|^6.0",
+        "symfony/process": "^5.2|^6.0"
     },
     "config": {
         "sort-packages": true,
diff --git a/src/HandlerResolver.php b/src/HandlerResolver.php
new file mode 100644
index 0000000..f9363e8
--- /dev/null
+++ b/src/HandlerResolver.php
@@ -0,0 +1,143 @@
+<?php declare(strict_types=1);
+
+namespace Bref\SymfonyBridge;
+
+use Bref\Runtime\FileHandlerLocator;
+use Bref\SymfonyBridge\Http\KernelAdapter;
+use Bref\SymfonyBridge\Runtime\BrefRuntime;
+use Exception;
+use Psr\Container\ContainerInterface;
+use Symfony\Component\HttpKernel\HttpKernelInterface;
+use Symfony\Component\HttpKernel\KernelInterface;
+
+/**
+ * This class resolves handlers.
+ *
+ * For example, if we configure `handler: xyz` in serverless.yml, then Bref
+ * will call this class to resolve `xyz` into the real Lambda handler.
+ */
+class HandlerResolver implements ContainerInterface
+{
+    private ?ContainerInterface $symfonyContainer;
+    private FileHandlerLocator $fileLocator;
+
+    public function __construct()
+    {
+        // Bref's default handler resolver
+        $this->fileLocator = new FileHandlerLocator;
+        $this->symfonyContainer = null;
+    }
+
+    /**
+     * {@inheritDoc}
+     */
+    public function get($id)
+    {
+        $isComposed = strpos($id, ':') !== false;
+
+        // By default we check if the handler is a file name (classic Bref behavior)
+        if (! $isComposed && $this->fileLocator->has($id)) {
+            return $this->fileLocator->get($id);
+        }
+
+        $service = $id;
+
+        $bootstrapFile = null;
+        if ($isComposed) {
+            [$bootstrapFile, $service] = explode(':', $id, 2);
+        }
+
+        // If not, we try to get the handler from the Symfony container
+        $handler = $this->symfonyContainer($bootstrapFile)->get($service);
+
+        // If the kernel was configured as a handler, then we wrap it to make it a valid HTTP handler for Lambda
+        if ($handler instanceof HttpKernelInterface) {
+            $handler = new KernelAdapter($handler);
+        }
+
+        return $handler;
+    }
+
+    /**
+     * {@inheritDoc}
+     */
+    public function has($id): bool
+    {
+        $isComposed = strpos($id, ':') !== false;
+
+        // By default we check if the handler is a file name (classic Bref behavior)
+        if (! $isComposed && $this->fileLocator->has($id)) {
+            return true;
+        }
+
+        $service = $id;
+
+        $bootstrapFile = null;
+        if ($isComposed) {
+            [$bootstrapFile, $service] = explode(':', $id, 2);
+        }
+
+        // If not, we try to get the handler from the Symfony container
+        return $this->symfonyContainer($bootstrapFile)->has($service);
+    }
+
+    /**
+     * Create and return the Symfony container.
+     */
+    private function symfonyContainer(?string $bootstrapFile = null): ContainerInterface
+    {
+        // Only create it once
+        if (! $this->symfonyContainer) {
+            $bootstrapFile = $bootstrapFile ?: 'public/index.php';
+
+            if (! file_exists($bootstrapFile)) {
+                throw new Exception(
+                    "Cannot find file '$bootstrapFile': the Bref-Symfony bridge tried to require that file to get the Symfony kernel. If your application does not have that file, follow the Bref-Symfony documentation to create and configure a file that returns the Symfony Kernel."
+                );
+            }
+
+            $app = require $bootstrapFile;
+
+            if (! is_object($app)) {
+                throw new Exception(sprintf(
+                    "The '%s' file must return an anonymous function (that returns the Symfony Kernel). Instead it returned '%s'. Either edit the file to return an anonymous function, or create a separate file (follow the online documentation to do so).",
+                    $bootstrapFile,
+                    // @phpstan-ignore-next-line
+                    is_object($app) ? get_class($app) : gettype($app),
+                ));
+            }
+
+            $projectDir = getenv('LAMBDA_TASK_ROOT') ?: null;
+
+            // Use the Symfony Runtime component to resolve the closure and get the PSR-11 container
+            $options = $_SERVER['APP_RUNTIME_OPTIONS'] ?? [];
+            if ($projectDir) {
+                $options['project_dir'] = $projectDir;
+            }
+            $runtime = new BrefRuntime($options);
+
+            [$app, $args] = $runtime
+                ->getResolver($app)
+                ->resolve();
+
+            $container = $app(...$args);
+
+            if ($container instanceof KernelInterface) {
+                $container->boot();
+                $container = $container->getContainer();
+            }
+
+            if (! $container instanceof ContainerInterface) {
+                throw new Exception(sprintf(
+                    "The closure returned by '%s' must return either a Symfony Kernel or a PSR-11 container. Instead it returned '%s'",
+                    $bootstrapFile,
+                    is_object($container) ? get_class($container) : gettype($container),
+                ));
+            }
+
+            $this->symfonyContainer = $container;
+        }
+
+        return $this->symfonyContainer;
+    }
+}
diff --git a/src/Http/KernelAdapter.php b/src/Http/KernelAdapter.php
new file mode 100644
index 0000000..941c4f2
--- /dev/null
+++ b/src/Http/KernelAdapter.php
@@ -0,0 +1,49 @@
+<?php declare(strict_types=1);
+
+namespace Bref\SymfonyBridge\Http;
+
+use Nyholm\Psr7\Factory\Psr17Factory;
+use Psr\Http\Message\ResponseInterface;
+use Psr\Http\Message\ServerRequestInterface;
+use Psr\Http\Server\RequestHandlerInterface;
+use Symfony\Bridge\PsrHttpMessage\Factory\HttpFoundationFactory;
+use Symfony\Bridge\PsrHttpMessage\Factory\PsrHttpFactory;
+use Symfony\Component\HttpKernel\HttpKernelInterface;
+use Symfony\Component\HttpKernel\TerminableInterface;
+
+/**
+ * This turns a Symfony Kernel into a PSR-15 handler.
+ *
+ * That means the Symfony Kernel can now be used by Bref (which supports PSR-15)
+ * to handle HTTP requests from API Gateway.
+ */
+class KernelAdapter implements RequestHandlerInterface
+{
+    private HttpKernelInterface $kernel;
+    // PSR-15 to Symfony converters
+    private HttpFoundationFactory $symfonyFactory;
+    private PsrHttpFactory $psrFactory;
+
+    public function __construct(HttpKernelInterface $kernel)
+    {
+        $this->kernel = $kernel;
+        $this->symfonyFactory = new HttpFoundationFactory;
+        $psr17Factory = new Psr17Factory;
+        $this->psrFactory = new PsrHttpFactory($psr17Factory, $psr17Factory, $psr17Factory, $psr17Factory);
+    }
+
+    public function handle(ServerRequestInterface $request): ResponseInterface
+    {
+        // From PSR-7 to Symfony
+        $symfonyRequest = $this->symfonyFactory->createRequest($request);
+
+        $symfonyResponse = $this->kernel->handle($symfonyRequest);
+
+        if ($this->kernel instanceof TerminableInterface) {
+            $this->kernel->terminate($symfonyRequest, $symfonyResponse);
+        }
+
+        // From Symfony to PSR-7
+        return $this->psrFactory->createResponse($symfonyResponse);
+    }
+}
diff --git a/src/Runtime/BrefRuntime.php b/src/Runtime/BrefRuntime.php
new file mode 100644
index 0000000..4ffddc8
--- /dev/null
+++ b/src/Runtime/BrefRuntime.php
@@ -0,0 +1,9 @@
+<?php declare(strict_types=1);
+
+namespace Bref\SymfonyBridge\Runtime;
+
+use Symfony\Component\Runtime\SymfonyRuntime;
+
+class BrefRuntime extends SymfonyRuntime
+{
+}
diff --git a/src/bootstrap.php b/src/bootstrap.php
new file mode 100644
index 0000000..0e451c1
--- /dev/null
+++ b/src/bootstrap.php
@@ -0,0 +1,14 @@
+<?php declare(strict_types=1);
+
+use Bref\Bref;
+use Bref\SymfonyBridge\HandlerResolver;
+
+/**
+ * File executed when the application starts: it registers a Bref PSR-11 "handler resolver".
+ *
+ * This is what Bref will use to turn handler names (strings defined in serverless.yml/AWS Lambda)
+ * into classes that can handle the Lambda events.
+ */
+if (class_exists(Bref::class)) {
+    Bref::setContainer(static fn () => new HandlerResolver);
+}
diff --git a/tests/Fixtures/MyService.php b/tests/Fixtures/MyService.php
new file mode 100644
index 0000000..7d58195
--- /dev/null
+++ b/tests/Fixtures/MyService.php
@@ -0,0 +1,7 @@
+<?php declare(strict_types=1);
+
+namespace Bref\SymfonyBridge\Test\Fixtures;
+
+class MyService
+{
+}
diff --git a/tests/Fixtures/TestKernel.php b/tests/Fixtures/TestKernel.php
new file mode 100644
index 0000000..a15b8e8
--- /dev/null
+++ b/tests/Fixtures/TestKernel.php
@@ -0,0 +1,51 @@
+<?php declare(strict_types=1);
+
+namespace Bref\SymfonyBridge\Test\Fixtures;
+
+use Bref\SymfonyBridge\BrefKernel;
+use Symfony\Bundle\FrameworkBundle\FrameworkBundle;
+use Symfony\Bundle\FrameworkBundle\Kernel\MicroKernelTrait;
+use Symfony\Component\DependencyInjection\ContainerBuilder;
+use Symfony\Component\DependencyInjection\Definition;
+use Symfony\Component\DependencyInjection\Loader\Configurator\ContainerConfigurator;
+
+class TestKernel extends BrefKernel
+{
+    use MicroKernelTrait;
+
+    public function __construct()
+    {
+        parent::__construct('dev', true);
+    }
+
+    public function registerBundles(): array
+    {
+        return [
+            new FrameworkBundle,
+        ];
+    }
+
+    /**
+     * @param ContainerBuilder|ContainerConfigurator $c
+     * @param mixed $loader
+     */
+    protected function configureContainer($c, $loader = null): void
+    {
+        if ($c instanceof  ContainerBuilder) {
+            $definition = new Definition(MyService::class);
+            $definition->setPublic(true);
+            $c->setDefinition(MyService::class, $definition);
+        } else {
+            $c->services()->set(MyService::class)->public();
+        }
+    }
+
+    /**
+     * This method is needed only for supporting lower Symfony versions
+     *
+     * @param mixed $routes
+     */
+    protected function configureRoutes($routes): void
+    {
+    }
+}
diff --git a/tests/TestKernel.php b/tests/TestKernel.php
deleted file mode 100644
index 22279d6..0000000
--- a/tests/TestKernel.php
+++ /dev/null
@@ -1,23 +0,0 @@
-<?php declare(strict_types=1);
-
-namespace Bref\SymfonyBridge\Test;
-
-use Bref\SymfonyBridge\BrefKernel;
-use Symfony\Component\Config\Loader\LoaderInterface;
-
-class TestKernel extends BrefKernel
-{
-    public function __construct()
-    {
-        parent::__construct('prod', false);
-    }
-
-    public function registerBundles(): array
-    {
-        return [];
-    }
-
-    public function registerContainerConfiguration(LoaderInterface $loader)
-    {
-    }
-}
diff --git a/tests/Unit/BrefKernelTest.php b/tests/Unit/BrefKernelTest.php
index e0180fd..8cf31e1 100644
--- a/tests/Unit/BrefKernelTest.php
+++ b/tests/Unit/BrefKernelTest.php
@@ -2,7 +2,7 @@
 
 namespace Bref\SymfonyBridge\Test\Unit;
 
-use Bref\SymfonyBridge\Test\TestKernel;
+use Bref\SymfonyBridge\Test\Fixtures\TestKernel;
 use PHPUnit\Framework\TestCase;
 
 class BrefKernelTest extends TestCase
@@ -10,9 +10,9 @@ class BrefKernelTest extends TestCase
     public function testIsLambda()
     {
         $kernel = new TestKernel;
-        $this->assertFalse($kernel->isLambda());
+        self::assertFalse($kernel->isLambda());
 
         putenv('LAMBDA_TASK_ROOT=/var/task');
-        $this->assertTrue($kernel->isLambda());
+        self::assertTrue($kernel->isLambda());
     }
 }
diff --git a/tests/Unit/HandlerResolverTest.php b/tests/Unit/HandlerResolverTest.php
new file mode 100644
index 0000000..79520d4
--- /dev/null
+++ b/tests/Unit/HandlerResolverTest.php
@@ -0,0 +1,57 @@
+<?php declare(strict_types=1);
+
+namespace Bref\SymfonyBridge\Test\Unit;
+
+use Bref\Bref;
+use Bref\SymfonyBridge\HandlerResolver;
+use Bref\SymfonyBridge\Http\KernelAdapter;
+use Bref\SymfonyBridge\Test\Fixtures\MyService;
+use Bref\SymfonyBridge\Test\Fixtures\TestKernel;
+use Closure;
+use PHPUnit\Framework\TestCase;
+use Psr\Http\Server\RequestHandlerInterface;
+
+class HandlerResolverTest extends TestCase
+{
+    private string $cwd;
+
+    public function setUp(): void
+    {
+        $this->cwd = getcwd();
+        chdir(__DIR__);
+    }
+
+    public function tearDown(): void
+    {
+        chdir($this->cwd);
+    }
+
+    public function test Bref uses our handler resolver()
+    {
+        self::assertInstanceOf(HandlerResolver::class, Bref::getContainer());
+    }
+
+    public function test files are resolved()
+    {
+        $resolver = new HandlerResolver;
+        self::assertTrue($resolver->has('fake-handler.php'));
+        $fileHandler = $resolver->get('fake-handler.php');
+        self::assertInstanceOf(Closure::class, $fileHandler);
+        self::assertEquals('hello world', $fileHandler());
+    }
+
+    public function test Symfony services can be used as Lambda handlers()
+    {
+        $resolver = new HandlerResolver;
+        self::assertInstanceOf(MyService::class, $resolver->get(MyService::class));
+        self::assertTrue($resolver->has(MyService::class));
+    }
+
+    public function test the Symfony kernel can be used as a HTTP handler()
+    {
+        $resolver = new HandlerResolver;
+        $handler = $resolver->get(TestKernel::class);
+        self::assertInstanceOf(RequestHandlerInterface::class, $handler);
+        self::assertInstanceOf(KernelAdapter::class, $handler);
+    }
+}
diff --git a/tests/Unit/fake-handler.php b/tests/Unit/fake-handler.php
new file mode 100644
index 0000000..1bed93a
--- /dev/null
+++ b/tests/Unit/fake-handler.php
@@ -0,0 +1,5 @@
+<?php declare(strict_types=1);
+
+return function () {
+    return 'hello world';
+};
diff --git a/tests/Unit/public/index.php b/tests/Unit/public/index.php
new file mode 100644
index 0000000..363d54e
--- /dev/null
+++ b/tests/Unit/public/index.php
@@ -0,0 +1,5 @@
+<?php declare(strict_types=1);
+
+return function () {
+    return new Bref\SymfonyBridge\Test\Fixtures\TestKernel;
+};