Usage

• Obtain Circuit Breaker
• Attempt
• Otherwise Callback
  • Default Otherwise Callback
• Retries & Failure Threshold
• Recovery (Half-Open)

Obtain Circuit Breaker

Once you have defined your "service" and circuit breaker settings, in your config/circuit-breaker, you can obtain a CircuitBreaker instance. This can be done via the CircuitBreakerManagerTrait.

<?php

use Aedart\Circuits\Traits\CircuitBreakerManagerTrait;

class WeatherService
{
    use CircuitBreakerManagerTrait;
    
    public function forecast()
    {
        // Obtain circuit breaker for "weather_service" (defined in your
        // config/circuit-breakers.php file)
        $circuitBreaker = $this->getCircuitBreakerManager()
            ->create('weather_service');
            
        // ...remaining not shown
    }
}

Attempt

Use the attempt() method to invoke a callback. Depending on your configuration, this callback will be attempted executed one or multiple times (See retries in your configuration file), until it either succeeds or fails entirely.

use Aedart\Contracts\Circuits\CircuitBreaker;

return $circuitBreaker->attempt(function(CircuitBreaker $cb) {
    // Call 3rd party service, return result ...
    $response = $http::get('https://acme.org/api/weather-service/v1/forecast');

    if ($response->failed()) {
        throw new RuntimeException('Unable to obtain forecast');
    }

    return $response;
});

Otherwise Callback

Use the $otherwise argument to state a callback, which will be invoked if the attempt should fail.

use Aedart\Contracts\Circuits\CircuitBreaker;
use Acme\Services\Weather\ServiceUnavailable;

return $circuitBreaker->attempt(function(CircuitBreaker $cb) {
    // ... callback not shown ...
}, function(CircuitBreaker $cb) {
    // Attempt has failed, do something else
    $lastFailure = $cb->lastFailure();
    $reason = $lastFailure->reason();

    if (!empty($reason)) {
        throw new ServiceUnavailable($reason);
    }
    
    throw new ServiceUnavailable('Weather Service is currently unavailable');
});

Behind the scenes, if the circuit breaker has detected too many failed attempts, across instances, then the $otherwise callback can be invoked immidiatly, allowing a fast-failure to occur. This happens when the failure_threshold has been reached.

Default Otherwise Callback

You may also specify a default otherwise callback to be invoked, when none provided via the attempt() method.

use Aedart\Contracts\Circuits\CircuitBreaker;

$result = $circuitBreaker
    ->otherwise(function(CircuitBreaker $cb) {
        // ...not shown...
    })
    ->attempt(function(CircuitBreaker $cb) {
        // ...callback not shown...
    });

Retries & Failure Threshold

It is very important to understand that, each failed attempt increases the failure count. The circuit breaker's internal store keeps track of this failure count, across instances. This means that, if you have configured your circuit breaker to perform a certain amount retries, it might not actually perform all attempts, if the failure_threshold is reached, during those attempts.

Please be mindful og how you choose to configure your retries and failure_threshold.

Recovery (Half-Open)

When the circuit breaker is in Open state (circuit tripped - failure state), it will automatically try to switch state to the Half-Open state, each time attempt() is invoked. However, this only happens after the grace_period has past (available in your configuration).

Note

By default, only a single circuit breaker instance will be able to obtain the Half-Open state, across instances.

If a circuit breaker achieves changing state to Half-Open, it will invoke the provided $callback. Should the callback succeed, then the failure count will be reset, across all instances. This means that the circuit breaker changes its state back to Closed.

If the callback does not succeed, the circuit breaker will remain in Open state and invoke the $otherwise callback.

Lastly, if the Half-Open state cannot be obtained, then the circuit breaker resumes its normal behaviour and invokes the $otherwise callback.