Feature Flagの設計と運用：本番環境での安全なリリース管理を実現する実装パターン

import os

def is_feature_enabled(feature_name: str) -> bool:
    """環境変数でFeature Flagを制御"""
    env_key = f"FEATURE_{feature_name.upper()}_ENABLED"
    return os.getenv(env_key, "false").lower() == "true"

# 使用例
if is_feature_enabled("new_checkout"):
    return new_checkout_flow(user)
else:
    return legacy_checkout_flow(user)

# config/feature_flags.yaml
features:
  new_checkout:
    enabled: true
    rollout_percentage: 50
  dark_mode:
    enabled: false
    allowed_users:
      - "beta_tester_1"
      - "beta_tester_2"

import yaml
import random

class FeatureFlagManager:
    def __init__(self, config_path: str):
        with open(config_path) as f:
            self.config = yaml.safe_load(f)

    def is_enabled(self, feature_name: str, user_id: str = None) -> bool:
        feature = self.config.get("features", {}).get(feature_name, {})

        if not feature.get("enabled", False):
            return False

        # 特定ユーザーのみ許可
        allowed_users = feature.get("allowed_users", [])
        if allowed_users and user_id in allowed_users:
            return True

        # ロールアウト率による制御
        rollout = feature.get("rollout_percentage", 100)
        return random.randint(1, 100) <= rollout

import hashlib

class GradualRollout:
    def __init__(self, feature_name: str, percentage: int):
        self.feature_name = feature_name
        self.percentage = percentage

    def is_enabled_for_user(self, user_id: str) -> bool:
        """ユーザーIDのハッシュ値で一貫した判定を行う"""
        hash_input = f"{self.feature_name}:{user_id}"
        hash_value = int(hashlib.md5(hash_input.encode()).hexdigest(), 16)
        bucket = hash_value % 100
        return bucket < self.percentage

# 使用例：10%のユーザーに新機能を公開
rollout = GradualRollout("new_dashboard", percentage=10)

# 同じユーザーには常に同じ結果が返る
print(rollout.is_enabled_for_user("user_123"))  # True or False（一貫）

from datetime import datetime, timedelta

class CanaryRelease:
    def __init__(self, feature_name: str, stages: list):
        """
        stages: [
            {"percentage": 1, "duration_hours": 2},
            {"percentage": 10, "duration_hours": 4},
            {"percentage": 50, "duration_hours": 24},
            {"percentage": 100, "duration_hours": None}
        ]
        """
        self.feature_name = feature_name
        self.stages = stages
        self.start_time = datetime.now()

    def get_current_percentage(self) -> int:
        elapsed = datetime.now() - self.start_time
        cumulative_hours = 0

        for stage in self.stages:
            if stage["duration_hours"] is None:
                return stage["percentage"]
            cumulative_hours += stage["duration_hours"]
            if elapsed < timedelta(hours=cumulative_hours):
                return stage["percentage"]

        return self.stages[-1]["percentage"]