pybreaker 1.2.0

事件监听

如果您只想在发生某些事件时采取行动，则无需子类化CircuitBreaker。在这种情况下，最好是子类化CircuitBreakerListener

class DBListener(pybreaker.CircuitBreakerListener):
    "Listener used by circuit breakers that execute database operations."

    def before_call(self, cb, func, *args, **kwargs):
        "Called before the circuit breaker `cb` calls `func`."
        pass

    def state_change(self, cb, old_state, new_state):
        "Called when the circuit breaker `cb` state changes."
        pass

    def failure(self, cb, exc):
        "Called when a function invocation raises a system error."
        pass

    def success(self, cb):
        "Called when a function invocation succeeds."
        pass

class LogListener(pybreaker.CircuitBreakerListener):
    "Listener used to log circuit breaker events."

    def state_change(self, cb, old_state, new_state):
        msg = "State Change: CB: {0}, New State: {1}".format(cb.name, new_state)
        logging.info(msg)

要将监听器添加到断路器

# At creation time...
db_breaker = pybreaker.CircuitBreaker(listeners=[DBListener(), LogListener()])

# ...or later
db_breaker.add_listeners(OneListener(), AnotherListener())

断路器做什么？

假设您想在更新customer数据库表中的行的函数上使用断路器

@db_breaker
def update_customer(cust):
    # Do stuff here...
    pass

# Will trigger the circuit breaker
updated_customer = update_customer(my_customer)

或者如果您不想使用装饰器语法

def update_customer(cust):
    # Do stuff here...
    pass

# Will trigger the circuit breaker
updated_customer = db_breaker.call(update_customer, my_customer)

或者将其用作上下文管理器以及一个with语句

# Will trigger the circuit breaker
with db_breaker.calling():
    # Do stuff here...
    pass

根据默认参数，断路器db_breaker将在update_customer中连续5次失败后自动打开电路。

当电路打开时，所有对update_customer的调用将立即失败（引发CircuitBreakerError），而不会尝试执行实际操作。如果您想在电路跳闸时抛出原始错误，请将throw_new_error_on_trip选项设置为False

pybreaker.CircuitBreaker(..., throw_new_error_on_trip=False)

60秒后，断路器将允许对update_customer的下一个调用通过。如果该调用成功，则电路关闭；如果失败，则电路再次打开，直到另一个超时到期。

可选的Tornado支持

断路器可以（可选地）用于调用异步Tornado函数

from tornado import gen

@db_breaker(__pybreaker_call_async=True)
@gen.coroutine
def async_update(cust):
    # Do async stuff here...
    pass

或者如果您不想使用装饰器语法

@gen.coroutine
def async_update(cust):
    # Do async stuff here...
    pass

updated_customer = db_breaker.call_async(async_update, my_customer)

排除异常

默认情况下，失败的调用是引发异常的任何调用。然而，通常还会抛出异常来指示业务异常，并且这些异常不应由断路器忽略，因为它们不表示系统错误

# At creation time...
db_breaker = CircuitBreaker(exclude=[CustomerValidationError])

# ...or later
db_breaker.add_excluded_exception(CustomerValidationError)

在这种情况下，当任何由该断路器保护的函数引发CustomerValidationError（或从CustomerValidationError派生的任何异常）时，该调用不会被视为系统故障。

为了覆盖仅使用异常类不足以确定它是否表示系统错误的情况，您也可以传递一个可调用对象而不是类型

db_breaker = CircuitBreaker(exclude=[lambda e: type(e) == HTTPError and e.status_code < 500])

您可以自由混合类型和过滤可调用对象。

监控和管理

断路器提供了一些属性和函数，您可以用来监控和更改其当前状态

# Get the current number of consecutive failures
print(db_breaker.fail_counter)

# Get/set the maximum number of consecutive failures
print(db_breaker.fail_max)
db_breaker.fail_max = 10

# Get/set the current reset timeout period (in seconds)
print db_breaker.reset_timeout
db_breaker.reset_timeout = 60

# Get the current state, i.e., 'open', 'half-open', 'closed'
print(db_breaker.current_state)

# Closes the circuit
db_breaker.close()

# Half-opens the circuit
db_breaker.half_open()

# Opens the circuit
db_breaker.open()

这些属性和函数可能并且应该以某种方式暴露给运维人员，因为它们有助于他们检测系统中的问题。