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Module: infrastructure.queue.retry_policy
Description: Retry policies and mechanisms for batch processing
Author: Anderson H. Silva
Date: 2025-01-25
License: Proprietary - All rights reserved
"""
from typing import Dict, Any, Optional, Callable, List
from datetime import datetime, timedelta
from dataclasses import dataclass
from enum import Enum
import random
import asyncio
from src.core import get_logger
logger = get_logger(__name__)
class RetryStrategy(str, Enum):
"""Retry strategy types."""
FIXED_DELAY = "fixed_delay"
EXPONENTIAL_BACKOFF = "exponential_backoff"
LINEAR_BACKOFF = "linear_backoff"
RANDOM_JITTER = "random_jitter"
FIBONACCI = "fibonacci"
@dataclass
class RetryPolicy:
"""Retry policy configuration."""
strategy: RetryStrategy = RetryStrategy.EXPONENTIAL_BACKOFF
max_attempts: int = 3
initial_delay: float = 1.0 # seconds
max_delay: float = 300.0 # 5 minutes
multiplier: float = 2.0 # for exponential backoff
jitter: bool = True # add randomness to prevent thundering herd
retry_on: Optional[List[type]] = None # specific exceptions to retry
dont_retry_on: Optional[List[type]] = None # exceptions to not retry
on_retry: Optional[Callable] = None # callback on retry
on_failure: Optional[Callable] = None # callback on final failure
class RetryHandler:
"""Handles retry logic for failed operations."""
def __init__(self, policy: RetryPolicy):
"""Initialize retry handler with policy."""
self.policy = policy
self._fibonacci_cache = {0: 0, 1: 1}
def should_retry(
self,
exception: Exception,
attempt: int
) -> bool:
"""
Determine if operation should be retried.
Args:
exception: The exception that occurred
attempt: Current attempt number (1-based)
Returns:
True if should retry
"""
# Check max attempts
if attempt >= self.policy.max_attempts:
logger.warning(
"max_retry_attempts_exceeded",
attempt=attempt,
max_attempts=self.policy.max_attempts
)
return False
# Check exception type
exc_type = type(exception)
# Check dont_retry_on list first
if self.policy.dont_retry_on:
if any(isinstance(exception, t) for t in self.policy.dont_retry_on):
logger.info(
"retry_skipped_exception_blacklist",
exception_type=exc_type.__name__
)
return False
# Check retry_on list
if self.policy.retry_on:
should_retry = any(isinstance(exception, t) for t in self.policy.retry_on)
if not should_retry:
logger.info(
"retry_skipped_exception_not_whitelisted",
exception_type=exc_type.__name__
)
return should_retry
# Default: retry on any exception
return True
def calculate_delay(self, attempt: int) -> float:
"""
Calculate delay before next retry.
Args:
attempt: Current attempt number (1-based)
Returns:
Delay in seconds
"""
base_delay = self._calculate_base_delay(attempt)
# Apply max delay cap
delay = min(base_delay, self.policy.max_delay)
# Apply jitter if enabled
if self.policy.jitter:
# Add random jitter of ±25%
jitter_range = delay * 0.25
delay += random.uniform(-jitter_range, jitter_range)
# Ensure minimum delay
delay = max(delay, 0.1)
logger.debug(
"retry_delay_calculated",
attempt=attempt,
delay=delay,
strategy=self.policy.strategy.value
)
return delay
def _calculate_base_delay(self, attempt: int) -> float:
"""Calculate base delay based on strategy."""
if self.policy.strategy == RetryStrategy.FIXED_DELAY:
return self.policy.initial_delay
elif self.policy.strategy == RetryStrategy.EXPONENTIAL_BACKOFF:
return self.policy.initial_delay * (self.policy.multiplier ** (attempt - 1))
elif self.policy.strategy == RetryStrategy.LINEAR_BACKOFF:
return self.policy.initial_delay * attempt
elif self.policy.strategy == RetryStrategy.RANDOM_JITTER:
# Random delay between initial and max
return random.uniform(
self.policy.initial_delay,
min(self.policy.initial_delay * 10, self.policy.max_delay)
)
elif self.policy.strategy == RetryStrategy.FIBONACCI:
return self.policy.initial_delay * self._fibonacci(attempt)
else:
return self.policy.initial_delay
def _fibonacci(self, n: int) -> int:
"""Calculate fibonacci number with memoization."""
if n in self._fibonacci_cache:
return self._fibonacci_cache[n]
# Calculate and cache
self._fibonacci_cache[n] = self._fibonacci(n - 1) + self._fibonacci(n - 2)
return self._fibonacci_cache[n]
async def execute_with_retry(
self,
func: Callable,
*args,
**kwargs
) -> Any:
"""
Execute function with retry logic.
Args:
func: Function to execute
*args: Function arguments
**kwargs: Function keyword arguments
Returns:
Function result
Raises:
Last exception if all retries fail
"""
last_exception = None
for attempt in range(1, self.policy.max_attempts + 1):
try:
# Execute function
if asyncio.iscoroutinefunction(func):
result = await func(*args, **kwargs)
else:
result = func(*args, **kwargs)
# Success - return result
if attempt > 1:
logger.info(
"retry_succeeded",
attempt=attempt,
function=func.__name__
)
return result
except Exception as e:
last_exception = e
# Check if should retry
if not self.should_retry(e, attempt):
if self.policy.on_failure:
await self._call_callback(
self.policy.on_failure,
e,
attempt
)
raise
# Calculate delay
delay = self.calculate_delay(attempt)
logger.warning(
"operation_failed_retrying",
attempt=attempt,
max_attempts=self.policy.max_attempts,
delay=delay,
error=str(e),
function=func.__name__
)
# Call retry callback if provided
if self.policy.on_retry:
await self._call_callback(
self.policy.on_retry,
e,
attempt,
delay
)
# Wait before retry
await asyncio.sleep(delay)
# All retries exhausted
if self.policy.on_failure:
await self._call_callback(
self.policy.on_failure,
last_exception,
self.policy.max_attempts
)
raise last_exception
async def _call_callback(
self,
callback: Callable,
exception: Exception,
attempt: int,
delay: Optional[float] = None
):
"""Call callback function safely."""
try:
if asyncio.iscoroutinefunction(callback):
await callback(exception, attempt, delay)
else:
callback(exception, attempt, delay)
except Exception as e:
logger.error(
"retry_callback_failed",
callback=callback.__name__,
error=str(e)
)
class CircuitBreaker:
"""
Circuit breaker pattern for preventing cascading failures.
States:
- CLOSED: Normal operation
- OPEN: Failing, reject all requests
- HALF_OPEN: Testing if service recovered
"""
class State(str, Enum):
CLOSED = "closed"
OPEN = "open"
HALF_OPEN = "half_open"
def __init__(
self,
failure_threshold: int = 5,
recovery_timeout: float = 60.0,
expected_exception: Optional[type] = None
):
"""
Initialize circuit breaker.
Args:
failure_threshold: Number of failures before opening
recovery_timeout: Seconds before attempting recovery
expected_exception: Exception type that triggers the breaker
"""
self.failure_threshold = failure_threshold
self.recovery_timeout = recovery_timeout
self.expected_exception = expected_exception
self.state = self.State.CLOSED
self.failure_count = 0
self.last_failure_time: Optional[datetime] = None
self.success_count = 0
def call(self, func: Callable, *args, **kwargs) -> Any:
"""
Call function through circuit breaker.
Args:
func: Function to call
*args: Function arguments
**kwargs: Function keyword arguments
Returns:
Function result
Raises:
Exception: If circuit is open or function fails
"""
if self.state == self.State.OPEN:
if self._should_attempt_reset():
self.state = self.State.HALF_OPEN
logger.info("circuit_breaker_half_open")
else:
raise Exception("Circuit breaker is OPEN")
try:
result = func(*args, **kwargs)
self._on_success()
return result
except Exception as e:
self._on_failure(e)
raise
async def call_async(
self,
func: Callable,
*args,
**kwargs
) -> Any:
"""Async version of call."""
if self.state == self.State.OPEN:
if self._should_attempt_reset():
self.state = self.State.HALF_OPEN
logger.info("circuit_breaker_half_open")
else:
raise Exception("Circuit breaker is OPEN")
try:
result = await func(*args, **kwargs)
self._on_success()
return result
except Exception as e:
self._on_failure(e)
raise
def _should_attempt_reset(self) -> bool:
"""Check if should attempt to reset circuit."""
return (
self.last_failure_time and
datetime.now() - self.last_failure_time > timedelta(seconds=self.recovery_timeout)
)
def _on_success(self):
"""Handle successful call."""
self.failure_count = 0
if self.state == self.State.HALF_OPEN:
self.success_count += 1
if self.success_count >= 3: # Require 3 successes
self.state = self.State.CLOSED
self.success_count = 0
logger.info("circuit_breaker_closed")
def _on_failure(self, exception: Exception):
"""Handle failed call."""
# Check if exception should trigger breaker
if self.expected_exception and not isinstance(exception, self.expected_exception):
return
self.failure_count += 1
self.last_failure_time = datetime.now()
if self.state == self.State.HALF_OPEN:
self.state = self.State.OPEN
logger.warning("circuit_breaker_opened_from_half_open")
elif self.failure_count >= self.failure_threshold:
self.state = self.State.OPEN
logger.warning(
"circuit_breaker_opened",
failures=self.failure_count,
threshold=self.failure_threshold
)
# Default retry policies
DEFAULT_RETRY_POLICY = RetryPolicy(
strategy=RetryStrategy.EXPONENTIAL_BACKOFF,
max_attempts=3,
initial_delay=1.0,
max_delay=60.0,
multiplier=2.0,
jitter=True
)
AGGRESSIVE_RETRY_POLICY = RetryPolicy(
strategy=RetryStrategy.EXPONENTIAL_BACKOFF,
max_attempts=5,
initial_delay=0.5,
max_delay=120.0,
multiplier=1.5,
jitter=True
)
GENTLE_RETRY_POLICY = RetryPolicy(
strategy=RetryStrategy.LINEAR_BACKOFF,
max_attempts=2,
initial_delay=5.0,
max_delay=30.0,
jitter=False
) |