AMQP with RabbitMQ

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Open up your .env file and check out the MESSENGER_TRANSPORT_DSN setting. We've been using the doctrine transport type. The doctrine://default string says that messages should be stored using Doctrine's default connection. In config/packages/messenger.yaml, we're referencing this environment variable for both the async and async_priority_high transports.

So... yep! We've been storing messages in a database table. It was quick to set up, easy to use - because we already understand databases - and robust enough for most use-cases.

Hello AMQP... RabbitMQ

But the industry standard "queueing system" or "message broker" is not a database table, it's something called AMQP, or "Advanced Message Queuing Protocol". AMQP is... not itself a technology... it's a "standard" for how a, so-called, "message broker system" should work. Then, different queuing systems can "implement" this standard. Honestly, usually when someone talks about AMQP, they're talking about one specific tool: RabbitMQ.

Here's the idea: in the same way that you launch a "database server" and make queries to it, you can launch a "Rabbit MQ instance" then send messages to it and receive messages from it. On a high level... it doesn't work much differently than our simple database table: you put messages in... then ask for them later.

So... what are the advantages of using RabbitMQ instead of Doctrine? Maybe... nothing! What I mean is, if you just use the standard Messenger features and never dig deeper, both will work just fine. But if you have a highly-scaled system or want to use some advanced, RabbitMQ-specific features, well... then... RabbitMQ is the answer!

What are those more advanced features? Well, stick with me over the next few chapters and you'll start to uncover them.

Launching an Instance via CloudAMQP.com

The easiest way to spin up a RabbitMQ instance is via cloudamqp.com: an awesome service for cloud-based RabbitMQ... with a free tier so we can play around! After logging in, create a new instance, give it a name, select any region... yep we do want the free tier and... "Create instance".

AMQP Transport Configuration

Cool! Click into the new instance to find... a beautiful AMQP connection string! Copy that, go find our .env file... and paste over doctrine://default. You can also put this into a .env.local file... which is what I would normally do so I can avoid committing these credentials.

Anyways, the amqp:// part activates the AMQP transport in Symfony... and the rest of this contains a username, password and other connection details. As soon as we make this change, both our async and async_priority_high transports... are now using RabbitMQ! That was easy!

Oh, but notice that I am still using doctrine for my failure transport... and I'm going to keep that. The failure transport is a special type of transport... and it turns out that the doctrine transport type actually has the most features for reviewing failed messages. You can use AMQP for this, but I recommend Doctrine.

Before we try this, I want to make one other change. Open up src/Controller/ImagePostController.php and find the create() method. This is the controller that's executed whenever we upload a photo... and it's responsible for dispatching the AddPonkaToImage command. It also adds a 500 millisecond delay via this stamp. Comment that out for now... I'll show you why we're doing this a bit later.

... lines 1 - 23
class ImagePostController extends AbstractController
{
... lines 26 - 40
public function create(Request $request, ValidatorInterface $validator, PhotoFileManager $photoManager, EntityManagerInterface $entityManager, MessageBusInterface $messageBus)
{
... lines 43 - 63
$envelope = new Envelope($message, [
//new DelayStamp(500)
]);
... lines 67 - 69
}
... lines 71 - 98
}

The AMQP PHP Extension

Ok! Other than removing that delay, all we've done is swap our transport config from Doctrine to AMQP. Let's... see if things still work! First, make sure your worker is not running... to begin with. Then, find your browser, select a photo and... it worked! Well, hold on... because you may have gotten a big AJAX error. If you did, open the profiler for that request. I'm pretty sure I know what error you'll see:

Attempted to load class "AMQPConnection" from the global namespace. Did you forget a "use" statement?

Why... no we did not! Under the hood, Symfony's AMQP transport type uses a PHP extension called... well... amqp! It's an add-on to PHP - like xdebug or pdo_mysql - that you'll probably need to install.

The pain with PHP extensions is that installing them can vary based on your system. For Ubuntu, you may be able to run

sudo apt-get install php-amqp

Or you might use pecl, like I did with my Homebrew Mac install:

pecl install amqp

Once you do manage to get it installed, make sure to restart the Symfony web server so that it sees the change. If you're having issues getting this configured, let us know in the comments and we'll do our best to help!

When it is all configured, you should be able upload a photo with no errors. And... because this had no errors... it... probably just got sent to RabbitMQ? When I refresh, it says "Ponka is napping"... because nothing has consumed our message yet. Well, let's see what happens. Find your terminal and consume messages from both of our transports:

php bin/console messenger:consume -vv async_priority_high async

And... there it is! It received the message, handled it... and it's done! When we refresh the page... there's Ponka! It worked! Switching from Doctrine to RabbitMQ was as simple as changing our connection string.

Next, let's dig deeper into what just happened behind the scenes: what does it mean to "send" a message to RabbitMQ or "get" a message from it? Oh, and you're going to love the RabbitMQ debugging tools.

Leave a comment!

  • 2020-05-31 weaverryan

    Hey Julien Bonnier!

    Hmm, I'm not sure! Here's what I would check. Open any page in your site, wait for the web debug toolbar to open, hover over the Symfony version on the bottom right, and then click View phpinfo(). This will show you the phpinfo() details. Is AMQP here? My guess is that it is *not* here... and so there's somethiung wrong with your Docker setup. It could be that your web browser is using a different php container (sometimes people have 2 containers for php - one for the cli and one for php-fpm) or something else.

    Cheers!

  • 2020-05-31 Julien Bonnier

    My error was You cannot use the "Symfony\Component\Messenger\Transport\AmqpExt\Connection" as the "amqp" extension is not installed.

    I'm using Docker with php:7.3.8-fpm-alpine3.10.

    I added to my Dockerfile something equvalent to:


    RUN apk add rabbitmq-c rabbitmq-c-dev
    RUN pecl install amqp
    RUN docker-php-ext-enable amqp
    RUN apk del --purge rabbitmq-c-dev

    Sould you have the same problem.

    Cheers