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from functools import wraps |
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from datetime import datetime, timedelta |
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STATE_CLOSED = 'closed' |
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STATE_OPEN = 'open' |
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STATE_HALF_OPEN = 'half_open' |
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class CircuitBreaker(object): |
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FAILURE_THRESHOLD = 5 |
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RECOVERY_TIMEOUT = 30 |
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EXPECTED_EXCEPTION = Exception |
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def __init__(self, |
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failure_threshold=None, |
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recovery_timeout=None, |
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expected_exception=None, |
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name=None): |
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self._failure_count = 0 |
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self._failure_threshold = failure_threshold or self.FAILURE_THRESHOLD |
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self._recovery_timeout = recovery_timeout or self.RECOVERY_TIMEOUT |
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self._expected_exception = expected_exception or self.EXPECTED_EXCEPTION |
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self._name = name |
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self._state = STATE_CLOSED |
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self._opened = datetime.utcnow() |
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def __call__(self, wrapped): |
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return self.decorate(wrapped) |
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def decorate(self, function): |
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""" |
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Applies the circuit breaker to a function |
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""" |
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if self._name is None: |
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self._name = function.__name__ |
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CircuitBreakerMonitor.register(self) |
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@wraps(function) |
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def wrapper(*args, **kwargs): |
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return self.call(function, *args, **kwargs) |
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return wrapper |
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def call(self, func, *args, **kwargs): |
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""" |
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Calls the decorated function and applies the circuit breaker |
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rules on success or failure |
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:param func: Decorated function |
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""" |
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if self.opened: |
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raise CircuitBreakerError(self) |
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try: |
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result = func(*args, **kwargs) |
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except self._expected_exception: |
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self.__call_failed() |
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raise |
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self.__call_succeeded() |
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return result |
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def __call_succeeded(self): |
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""" |
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Close circuit after successful execution and reset failure count |
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""" |
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self._state = STATE_CLOSED |
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self._failure_count = 0 |
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def __call_failed(self): |
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""" |
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Count failure and open circuit, if threshold has been reached |
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""" |
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self._failure_count += 1 |
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if self._failure_count >= self._failure_threshold: |
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self._state = STATE_OPEN |
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self._opened = datetime.utcnow() |
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@property |
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def state(self): |
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if self._state == STATE_OPEN and self.open_remaining <= 0: |
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return STATE_HALF_OPEN |
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return self._state |
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@property |
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def open_until(self): |
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""" |
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The datetime, when the circuit breaker will try to recover |
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:return: datetime |
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""" |
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return self._opened + timedelta(seconds=self._recovery_timeout) |
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@property |
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def open_remaining(self): |
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""" |
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Number of seconds remaining, the circuit breaker stays in OPEN state |
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:return: int |
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""" |
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return (self.open_until - datetime.utcnow()).total_seconds() |
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@property |
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def failure_count(self): |
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return self._failure_count |
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@property |
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def closed(self): |
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return self.state == STATE_CLOSED |
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@property |
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def opened(self): |
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return self.state == STATE_OPEN |
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@property |
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def name(self): |
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return self._name |
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def __str__(self, *args, **kwargs): |
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return self._name |
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class CircuitBreakerError(Exception): |
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def __init__(self, circuit_breaker, *args, **kwargs): |
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""" |
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:param circuit_breaker: |
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:param args: |
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:param kwargs: |
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:return: |
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""" |
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super().__init__(*args, **kwargs) |
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self._circuit_breaker = circuit_breaker |
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def __str__(self, *args, **kwargs): |
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return 'Circuit "%s" OPEN until %s (%d failures, %d sec remaining)' % ( |
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self._circuit_breaker.name, |
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self._circuit_breaker.open_until, |
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self._circuit_breaker.failure_count, |
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round(self._circuit_breaker.open_remaining) |
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) |
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class CircuitBreakerMonitor(object): |
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circuit_breakers = {} |
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143
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@classmethod |
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def register(cls, circuit_breaker): |
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cls.circuit_breakers[circuit_breaker.name] = circuit_breaker |
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147
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@classmethod |
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def all_closed(cls) -> bool: |
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return len(list(cls.get_open())) == 0 |
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@classmethod |
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def get_circuits(cls) -> [CircuitBreaker]: |
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return cls.circuit_breakers.values() |
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@classmethod |
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def get(cls, name) -> CircuitBreaker: |
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return cls.circuit_breakers.get(name) |
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159
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@classmethod |
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def get_open(cls) -> [CircuitBreaker]: |
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for circuit in cls.get_circuits(): |
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if circuit.opened: |
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yield circuit |
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@classmethod |
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def get_closed(cls) -> [CircuitBreaker]: |
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for circuit in cls.get_circuits(): |
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if circuit.closed: |
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yield circuit |
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def circuit(failure_threshold=None, |
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recovery_timeout=None, |
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expected_exception=None, |
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name=None, |
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cls=CircuitBreaker): |
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# if the decorator is used without parameters, the |
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# wrapped function is provided as first argument |
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if callable(failure_threshold): |
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return cls().decorate(failure_threshold) |
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else: |
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return cls( |
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failure_threshold=failure_threshold, |
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recovery_timeout=recovery_timeout, |
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expected_exception=expected_exception, |
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name=name) |
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fabfuel /
circuitbreaker
