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debug:container & Cache Config

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I want to talk more about this key: markdown.parser.light:

knp_markdown:
parser:
service: markdown.parser.light

We got this from the documentation: it told us that there are five different valid values that we can put for the service key.

But, this is more than just a random config key that the bundle author dreamt up. Remember: all services live inside an object called the container. And each has an internal name, or id.

It's not really important, but it turns out that markdown.parser.light is the id of a service in the container! Yep, with this config, we're telling the bundle that when we ask for the Markdown parser - like we are in the controller - it should now pass us the service that has this id.

Go to your terminal and run:

./bin/console debug:autowiring

And scroll to the top. Check this out! The MarkdownInterface is now an alias to markdown.parser.light! Before the config change, this was markdown.parser.max. Yep, this literally means that when we use MarkdownInterface, Symfony will pass us a service whose id is markdown.parser.light.

Normally, you do not need to worry about all of this. I mean, if you just want to use this bundle and configure a few things, follow its docs, make some config tweaks, go on a space walk, and then keep going!

The Many other Services in the Container

But we're on a quest to really understand how things work! Here's the truth, this is not a full list of all of the services in the container. Nope, not even close. This time, run:

./bin/console debug:container --show-private

This is actually the full list of the many services in the container. The service id is on the left, and the class for that object is on the right. Don't worry about the --show-private flag: that just makes sure this lists everything.

But, in reality, most of these services are internal, boring objects that you'll never use. The most important services show up in debug:autowiring and are really easy to access.

But yea... you can also fetch and use any of these services, and sometimes you'll need to. I'll show you how a bit later.

But here are the two big takeaways:

  1. There are many services in the container and each has an id.
  2. The services you'll use 99% of the time show up in debug:autowiring and are easy to access.

Configuring the Cache Object

Let's play with one more object. Instead of dumping $markdown, dump the $cache object:

... lines 1 - 13
class ArticleController extends AbstractController
{
... lines 16 - 26
public function show($slug, MarkdownInterface $markdown, AdapterInterface $cache)
{
... lines 29 - 53
dump($cache);die;
... lines 55 - 67
}
... lines 69 - 80
}

Find your page and refresh! Interesting: it's something called a TraceableAdapter, and, inside, a FilesystemAdapter!

So I guess our cache is being saved to the filesystem... and we can even see where in var/cache/dev/pools.

So... how can we configure the cache service? Of course, the easiest answer is just to Google its docs. But, we don't even need to do that! The cache service is provided by the FrameworkBundle, which is the one bundle that came automatically with our app.

Debugging your Current Config

Tip

In a recent change to the recipe, the cache config now lives in its own file config/packages/cache.yaml

Open framework.yaml and scroll down:

framework:
... lines 2 - 16
cache:
# Put the unique name of your app here: the prefix seed
# is used to compute stable namespaces for cache keys.
#prefix_seed: your_vendor_name/app_name
# The app cache caches to the filesystem by default.
# Other options include:
# Redis
#app: cache.adapter.redis
#default_redis_provider: redis://localhost
# APCu (not recommended with heavy random-write workloads as memory fragmentation can cause perf issues)
#app: cache.adapter.apcu

Hey! This file even comes with documentation about how to configure the cache! Of course, to get an even bigger example, we can run:

./bin/console config:dump framework

Here's the cache section, with some docs about the different keys. Now, try a slightly different command:

./bin/console debug:config framework

Instead of dumping example config, this is our current config! Under cache, there are 6 configured keys. But, you won't see all of these in framework.yaml: these are the bundle's default values. And yea! You can see that this app key is set to cache.adapter.filesystem.

Changing to an APCu Cache

The docs in framework.yaml tell us that, yep, if we want to change the cache system, app is the key we want. Let's uncomment the last one to set app to use APCu: an in-memory cache that's not as awesome as Redis, but easier to install:

framework:
... lines 2 - 16
cache:
... lines 18 - 28
# APCu (not recommended with heavy random-write workloads as memory fragmentation can cause perf issues)
app: cache.adapter.apcu

And just like with markdown, cache.adapter.apcu is a service that already exists in the container.

Ok, go back and refresh! Yes! The cache is now using an APCuAdapter internally!

Tip

Fun fact! Running ./bin/console cache:clear clears Symfony's internal cache that helps your app run. But, it purposely does not clear anything that you store in cache. If you want to clear that, run ./bin/console cache:pool:clear cache.app.

Bundle Config: the Good & Bad

So the great thing about configuring bundles is that you can make powerful changes with very simple config tweaks. You can also dump your config and Symfony will give you a great error if you have any typos.

The downside about configuring bundles is that... you really need to rely on the debug tools and documentation. I mean, there's no way we could sit here long enough and eventually figure out that the cache system is configured under framework, cache, app: the config structure is totally invented by the bundle.

Let's go back to our controller and remove that dump:

... lines 1 - 13
class ArticleController extends AbstractController
{
... lines 16 - 26
public function show($slug, MarkdownInterface $markdown, AdapterInterface $cache)
{
... lines 29 - 53
dump($cache);die;
... lines 55 - 67
}
... lines 69 - 80
}

Make sure everything still works. Perfect! If you get an error, make sure to install the APCu PHP extension.

Next, let's explore Symfony environments and totally demystify the purpose of each file in config/.

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