1
|
1 |
|
from functools import wraps |
2
|
1 |
|
from datetime import datetime, timedelta |
3
|
|
|
|
4
|
1 |
|
STATE_CLOSED = 'closed' |
5
|
1 |
|
STATE_OPEN = 'open' |
6
|
1 |
|
STATE_HALF_OPEN = 'half_open' |
7
|
|
|
|
8
|
|
|
|
9
|
1 |
|
class CircuitBreaker(object): |
10
|
1 |
|
FAILURE_THRESHOLD = 5 |
11
|
1 |
|
RECOVERY_TIMEOUT = 30 |
12
|
1 |
|
EXPECTED_EXCEPTION = Exception |
13
|
|
|
|
14
|
1 |
|
def __init__(self, |
15
|
|
|
failure_threshold=None, |
16
|
|
|
recovery_timeout=None, |
17
|
|
|
expected_exception=None, |
18
|
|
|
name=None): |
19
|
1 |
|
self._failure_count = 0 |
20
|
1 |
|
self._failure_threshold = failure_threshold or self.FAILURE_THRESHOLD |
21
|
1 |
|
self._recovery_timeout = recovery_timeout or self.RECOVERY_TIMEOUT |
22
|
1 |
|
self._expected_exception = expected_exception or self.EXPECTED_EXCEPTION |
23
|
1 |
|
self._name = name |
24
|
1 |
|
self._state = STATE_CLOSED |
25
|
1 |
|
self._opened = datetime.utcnow() |
26
|
|
|
|
27
|
1 |
|
def __call__(self, wrapped): |
28
|
1 |
|
return self.decorate(wrapped) |
29
|
|
|
|
30
|
1 |
|
def decorate(self, function): |
31
|
|
|
""" |
32
|
|
|
Applies the circuit breaker to a function |
33
|
|
|
""" |
34
|
1 |
|
if self._name is None: |
35
|
1 |
|
self._name = function.__name__ |
36
|
|
|
|
37
|
1 |
|
CircuitBreakerMonitor.register(self) |
38
|
|
|
|
39
|
1 |
|
@wraps(function) |
40
|
|
|
def wrapper(*args, **kwargs): |
41
|
1 |
|
return self.call(function, *args, **kwargs) |
42
|
|
|
|
43
|
1 |
|
return wrapper |
44
|
|
|
|
45
|
1 |
|
def call(self, func, *args, **kwargs): |
46
|
|
|
""" |
47
|
|
|
Calls the decorated function and applies the circuit breaker |
48
|
|
|
rules on success or failure |
49
|
|
|
:param func: Decorated function |
50
|
|
|
""" |
51
|
1 |
|
if self.opened: |
52
|
1 |
|
raise CircuitBreakerError(self) |
53
|
1 |
|
try: |
54
|
1 |
|
result = func(*args, **kwargs) |
55
|
1 |
|
except self._expected_exception: |
56
|
1 |
|
self.__call_failed() |
57
|
1 |
|
raise |
58
|
|
|
|
59
|
1 |
|
self.__call_succeeded() |
60
|
1 |
|
return result |
61
|
|
|
|
62
|
1 |
|
def __call_succeeded(self): |
63
|
|
|
""" |
64
|
|
|
Close circuit after successful execution and reset failure count |
65
|
|
|
""" |
66
|
1 |
|
self._state = STATE_CLOSED |
67
|
1 |
|
self._failure_count = 0 |
68
|
|
|
|
69
|
1 |
|
def __call_failed(self): |
70
|
|
|
""" |
71
|
|
|
Count failure and open circuit, if threshold has been reached |
72
|
|
|
""" |
73
|
1 |
|
self._failure_count += 1 |
74
|
1 |
|
if self._failure_count >= self._failure_threshold: |
75
|
1 |
|
self._state = STATE_OPEN |
76
|
1 |
|
self._opened = datetime.utcnow() |
77
|
|
|
|
78
|
1 |
|
@property |
79
|
|
|
def state(self): |
80
|
1 |
|
if self._state == STATE_OPEN and self.open_remaining <= 0: |
81
|
1 |
|
return STATE_HALF_OPEN |
82
|
1 |
|
return self._state |
83
|
|
|
|
84
|
1 |
|
@property |
85
|
|
|
def open_until(self): |
86
|
|
|
""" |
87
|
|
|
The datetime, when the circuit breaker will try to recover |
88
|
|
|
:return: datetime |
89
|
|
|
""" |
90
|
1 |
|
return self._opened + timedelta(seconds=self._recovery_timeout) |
91
|
|
|
|
92
|
1 |
|
@property |
93
|
|
|
def open_remaining(self): |
94
|
|
|
""" |
95
|
|
|
Number of seconds remaining, the circuit breaker stays in OPEN state |
96
|
|
|
:return: int |
97
|
|
|
""" |
98
|
1 |
|
return (self.open_until - datetime.utcnow()).total_seconds() |
99
|
|
|
|
100
|
1 |
|
@property |
101
|
|
|
def failure_count(self): |
102
|
1 |
|
return self._failure_count |
103
|
|
|
|
104
|
1 |
|
@property |
105
|
|
|
def closed(self): |
106
|
1 |
|
return self.state == STATE_CLOSED |
107
|
|
|
|
108
|
1 |
|
@property |
109
|
|
|
def opened(self): |
110
|
1 |
|
return self.state == STATE_OPEN |
111
|
|
|
|
112
|
1 |
|
@property |
113
|
|
|
def name(self): |
114
|
1 |
|
return self._name |
115
|
|
|
|
116
|
1 |
|
def __str__(self, *args, **kwargs): |
117
|
1 |
|
return self._name |
118
|
|
|
|
119
|
|
|
|
120
|
1 |
|
class CircuitBreakerError(Exception): |
121
|
1 |
|
def __init__(self, circuit_breaker, *args, **kwargs): |
122
|
|
|
""" |
123
|
|
|
:param circuit_breaker: |
124
|
|
|
:param args: |
125
|
|
|
:param kwargs: |
126
|
|
|
:return: |
127
|
|
|
""" |
128
|
1 |
|
super().__init__(*args, **kwargs) |
129
|
1 |
|
self._circuit_breaker = circuit_breaker |
130
|
|
|
|
131
|
1 |
|
def __str__(self, *args, **kwargs): |
132
|
1 |
|
return 'Circuit "%s" OPEN until %s (%d failures, %d sec remaining)' % ( |
133
|
|
|
self._circuit_breaker.name, |
134
|
|
|
self._circuit_breaker.open_until, |
135
|
|
|
self._circuit_breaker.failure_count, |
136
|
|
|
round(self._circuit_breaker.open_remaining) |
137
|
|
|
) |
138
|
|
|
|
139
|
|
|
|
140
|
1 |
|
class CircuitBreakerMonitor(object): |
141
|
1 |
|
circuit_breakers = {} |
142
|
|
|
|
143
|
1 |
|
@classmethod |
144
|
|
|
def register(cls, circuit_breaker): |
145
|
1 |
|
cls.circuit_breakers[circuit_breaker.name] = circuit_breaker |
146
|
|
|
|
147
|
1 |
|
@classmethod |
148
|
1 |
|
def all_closed(cls) -> bool: |
149
|
1 |
|
return len(list(cls.get_open())) == 0 |
150
|
|
|
|
151
|
1 |
|
@classmethod |
152
|
1 |
|
def get_circuits(cls) -> [CircuitBreaker]: |
153
|
1 |
|
return cls.circuit_breakers.values() |
154
|
|
|
|
155
|
1 |
|
@classmethod |
156
|
1 |
|
def get(cls, name) -> CircuitBreaker: |
157
|
1 |
|
return cls.circuit_breakers.get(name) |
158
|
|
|
|
159
|
1 |
|
@classmethod |
160
|
1 |
|
def get_open(cls) -> [CircuitBreaker]: |
161
|
1 |
|
for circuit in cls.get_circuits(): |
162
|
1 |
|
if circuit.opened: |
163
|
1 |
|
yield circuit |
164
|
|
|
|
165
|
1 |
|
@classmethod |
166
|
1 |
|
def get_closed(cls) -> [CircuitBreaker]: |
167
|
1 |
|
for circuit in cls.get_circuits(): |
168
|
1 |
|
if circuit.closed: |
169
|
1 |
|
yield circuit |
170
|
|
|
|
171
|
|
|
|
172
|
1 |
|
def circuit(failure_threshold=None, |
173
|
|
|
recovery_timeout=None, |
174
|
|
|
expected_exception=None, |
175
|
|
|
name=None, |
176
|
|
|
cls=CircuitBreaker): |
177
|
|
|
|
178
|
|
|
# if the decorator is used without parameters, the |
179
|
|
|
# wrapped function is provided as first argument |
180
|
1 |
|
if callable(failure_threshold): |
181
|
1 |
|
return cls().decorate(failure_threshold) |
182
|
|
|
else: |
183
|
1 |
|
return cls( |
184
|
|
|
failure_threshold=failure_threshold, |
185
|
|
|
recovery_timeout=recovery_timeout, |
186
|
|
|
expected_exception=expected_exception, |
187
|
|
|
name=name) |
188
|
|
|
|