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Command Queue Bundle

Bundle implementing command queue mechanism, making it possible to send command from main Symfony process and execute them using pools of backend workers using gendoria/command-queue library.

Bundle created in cooperation with Isobar Poland.

Installation

Step 1: Download the Bundle

Open a command console, enter your project directory and execute the following command to download the latest stable version of this bundle:

This command requires you to have Composer installed globally, as explained in the installation chapter of the Composer documentation.

Step 2: Enable the Bundle

Then, enable the bundle by adding it to the list of registered bundles in the app/AppKernel.php file of your project:

Step 3: Add bundle configuration

To be able to use the bundle, you have to add correct configuration in your app/config/config.yml.

The example full bundle configuration looks as follows:

enabled property allows to enable or disable bundle (eg. on some environments like testing).

listeners section is optional. By default all listeners are turned on.

Pools section describes available queue pools. It is required, when bundle is enabled. At least one pool, named default has to be present.

Pool configuration has only one parameter, send_driver. It describes, which method will be used to transport commands from sender to workers. Right now, the bundle does not provide any transportation method by itself (except of direct processing driver). There is, though, gendoria/command-queue-rabbitmq-bundle with transport implementation using RabbitMQ and php-amqplib/rabbitmq-bundle library.

Next section is optional routes. It allows defining command routes, sending specific command classes to different pools. Routes is a hash map. The key is command class expression and the value - target pool name. Every target pool has to be defined in pools section. More informations about command class expressions can be found in routing section.

Routing is completely optional. If not defined, all commands will be send to default pool. Also, for every command class with no routing defined, default pool will be used.

Usage

This bundle makes it possible to create a distributed execution environment for varius commands. Developer can use it for example to delegate processor - heavy tasks for backend execution instead of processing them in frontend (thus impairing user experience).

Command classes

Command class is where everything starts. It is used to pass any data required to process a command to a worker pool.

Command class has to implement Gendoria\CommandQueue\Command\CommandInterface. The interface itself does not contain any methods. It is used to 'tag' a class as a command.

Command class can contain any serializable values. They can be simple types, like integers or strings, but they can also be objects or arrays. They should not be resources, like database connections or file handles, as these are not serializable.

The example command class can look like below. This specific command uses JMS serializer, but you can use other serialization method, if you want. Command queue bundle provides implementation for JMS and Symfony serialization components.

As you can see, it has two public properties, URL and user ID. It is a simple value object without a logic on its own. This is a suggested way, but you can include some logic inside of it.

Command serialization

Command will be sent through some kind of queue, potentially to a completely different machine. As most transports cannot pass raw php object, commands have to be serialized to string representations.

This is done by serializer classes. In most cases you will not use them directly. They are injected to send drivers and executed on your command class. You have to provide a configuration for them, though.

Command above used JMS serializer. This is the preferred method, but bundle provides you with two other options.

Each serializer implements the Gendoria\CommandQueue\Serializer\SerializerInterface.

JMS Serializer

This serializer is available as a service gendoria_command_queue.serializer.jms. It uses jms/serializer-bundle component to create a serialized command representation. All usage instruction can be found on JMSSerializerBundle documentation.

Symfony serializer

This serializer is available as a service gendoria_command_queue.serializer.symfony. It uses Symfony serialization component.

This driver is in development phase. No detailed configuration instructions are present at the moment. You are welcome to submit one.

:warning: Warning! This serializer may not be available, if you use jms/serializer-bundle and it registeres its own service as serializer. There is a enable_short_alias key in JMS serializer configuration, that can change this behaviour.

Null serializer

This serializer is available as a service gendoria_command_queue.serializer.null.

In some cases you don't have to serialize a command. For this, null serializer can be used. It exists, though, mainly for testing purposes and has little real world usage.

Sending commands

Commands are sent using queue manager service. It is responsible of routing the command to the appropriate pool based on its configuration.

Bundle provides you with simple queue managers for each pool you define and one multiple queue manager, which uses routing to decide, onto which pool command will be sent.

Main queue manager can be accessed as gendoria_command_queue.manager service. Simple queue managers are accessible as services gendoria_command_queue.manager.poolName, where poolName is your pool name defined in pools configuration.

If you want to use queue manager inside your controller, you can call it like below. We use same ParseUrlCommand, as in command example above.

Command processors

The command has been created and sent. Now you have to process it somehow. Luckily, this is quite simple.

First, you have to create a command processor service. This is a class implementing ``.

This class has to have two function. First - supports - returns true, if command processor can process given command. In most cases you will just check, if the command is an instance of a given class.

Second function - process - is where command processing actually takes place.

When you have your service class, you have to register it as a service and tag with command processor tag. For the processor above, configuration can look like following.

The service cannot be abstract or private, as services are lazy loaded, when the command comes from queue.

That's it!

Routing

By default, bundle passes all commands to default queue (and default worker pool). If you want some commands to be executed by a specific set of workers, you can use routing. One posible use case could be, that you want to send e-mails to users from a specific server, not your default backend one. Or you have some commands so heavy in processing (like video reencoding), that they would have clogged your default queue. Then you can use routing to send these commands to a specialized pool of workers.

When using multiple queue manager provided by the bundle, you can define your routes inside your configuration file. One route entry is a hashmap, where key is route expression and the value - target pool name.

When matching routes, manager uses name of a command class and its ancestors, as well, as interfaces implemented by the command and its ancestors. Several rues apply here:

• Class names are always more important than interface names
• Child class name is more important, than the ancestors class names
• When comparying interfaces, interfaces implemented by the child class are more important, than these implemented by the base class.
• If nothing is detected, default pool is used

So, if you have a class X implementing interface Y and routes for both X and Y, route for X will be used.

If you have class with inheritance A -> B -> C, where A is most base class and C - child class, routing for C will be used. If no routing for C exists, manager considers routing for B and then A. If nothing is detected, default pool will be used.

Additionally, you can use * in your route expression to indicate any string value. So, for example, if your expression is *Something it will match class ASomething and BSomething, but not SomethingC. Similary, expression Example\Namespace\* will match all commands in example namespace.

Wildcard routes are less important, than simple routes on single class / interface comparision. When inheritance and / or interfaces come onto play, it becomes more complex and harder to tell. We advise to use routing on most child classes, using wildcards, and not to create routing for base classes / interfaces, unless absolutely necessary.

Send drivers

Bundle can use arbitrary transportation mechanisms to send commands to command processors. These mechanisms are called 'send drivers'.

By default, bundle provides only direct processing driver service. It executes command right after it is send, on same process as sender. It does not serialize command prior sending, so no serialization configuration is needed.

Other send drivers (eg. one using RabbitMQ queue mechanism) are provided by separate bundles.

Queue managers

Documentation in progress