Merge pull request #28 from Nyholm/readme

Added a first attempt for a readme

README.md

@@ -12,9 +12,87 @@ composer req bref/symfony-bridge
 
 ## Usage
 
-Update your Kernel.php
+You only need to one one small change To quickly setup Symfony to work with Bref.
 
 ```diff
+// src/Kernel.php
+
+namespace App;
+
+use App\Repository\Test\TestRepository;
++ Bref\SymfonyBridge\BrefKernel;
+use Symfony\Bundle\FrameworkBundle\Kernel\MicroKernelTrait;
+use Symfony\Component\Config\Loader\LoaderInterface;
+use Symfony\Component\Config\Resource\FileResource;
+use Symfony\Component\DependencyInjection\ContainerBuilder;
+-use Symfony\Component\HttpKernel\Kernel as BaseKernel;
+use Symfony\Component\Routing\RouteCollectionBuilder;
+
 - class Kernel extends BaseKernel
 + class Kernel extends BrefKernel
+{
+    // ...
+```
+
+Now you are up and running.
+
+## Optimize first request
+
+The first HTTP request that hits your application after you deployed a new version
+will use a cold cache directory. Symfony now spends time building thc cache. It may
+take everything between 1-20 seconds depending on the complexity of the application.
+
+Technically this happens whenever your application run on a new Lambda. That could
+be when you get a lot more traffic so AWS increases the resources or when AWS just
+decides to kill the lambda function (or server) that you are currently on. It is
+normal that this happens at least a handful of times every day.
+
+To optimize the first request, one must deploy the application with a warm cache.
+In a simple application it means that the deploy script should include `cache:warmup`
+to look something like this:
+
+```bash
+# Install dependencies
+composer install --classmap-authoritative --no-dev --no-scripts
+
+# Warmup the cache
+bin/console cache:warmup --env=prod
+
+# Disable use of Dotenv component
+echo "<?php return [];" > .env.local.php
+
+serverless deploy
+```
+
+## Optimize cache
+
+When running Symfony on Lambda you should avoid writing to the filesystem. If
+you prewarm the cache before deploy you are mostly fine. But you should also make
+sure you never write to a filesystem cache like `cache.system` or use a pool like:
+
+```yaml
+framework:
+    cache:
+        pools:
+            my_pool:
+                adapter: cache.adapter.filesystem
+```
+
+If you dont write to such cache pool you can optimize your setup by not copy the
+`var/cache/pools` directory. The change below will make sure to symlink the `pools`
+directory.
+
+```diff
+// src/Kernel.php
+
+
+class Kernel extends BrefKernel
+{
+    // ...
+
++    protected function getWritableCacheDirectories(): array
++    {
++        return [];
++    }
+}
 ```