legacy

遗留系统现代化

安全地升级并改造遗留系统。

适用场景

• 框架迁移
• 语言版本升级
• 单体应用拆分
• 技术债务削减
• 依赖更新

迁移策略

绞杀者无花果模式

┌─────────────────────────────────────┐
│           Load Balancer             │
└──────────────┬──────────────────────┘
               │
       ┌───────┴───────┐
       │               │
┌──────▼──────┐ ┌──────▼──────┐
│   Legacy    │ │    New      │
│   System    │ │   Service   │
└─────────────┘ └─────────────┘

1. Route new features to new service
2. Gradually migrate existing features
3. Eventually retire legacy system

通过抽象进行分支

# 1. Create abstraction layer
class PaymentProcessor(ABC):
    @abstractmethod
    def process(self, amount: float) -> bool:
        pass

# 2. Wrap legacy implementation
class LegacyPaymentProcessor(PaymentProcessor):
    def __init__(self, legacy_system):
        self.legacy = legacy_system

    def process(self, amount: float) -> bool:
        return self.legacy.old_process_method(amount)

# 3. Create new implementation
class ModernPaymentProcessor(PaymentProcessor):
    def process(self, amount: float) -> bool:
        # New implementation
        pass

# 4. Use feature flag to switch
processor = (ModernPaymentProcessor() if feature_flag("new_payment")
             else LegacyPaymentProcessor(legacy))

迁移检查清单

开始之前

• 记录当前行为
• 为现有功能添加测试
• 设置监控和告警
• 制定回滚计划
• 与利益相关者沟通

迁移期间

• 进行增量更改
• 每次更改后都进行测试
• 监控错误率
• 保持遗留系统并行运行
• 记录破坏性更改

迁移之后

• 移除功能标志
• 清理遗留代码
• 更新文档
• 归档旧代码库
• 总结经验教训

常见迁移

从 jQuery 迁移到 React

// Phase 1: Embed React in jQuery app
const root = document.getElementById("new-component");
ReactDOM.render(<NewComponent />, root);

// Phase 2: Shared state
window.appState = { user: null };
// Both jQuery and React read from appState

// Phase 3: Gradual replacement
// Replace one component at a time

从 Python 2 迁移到 3

# Use __future__ imports for compatibility
from __future__ import print_function, division, absolute_import

# Use six for cross-version compatibility
import six
if six.PY2:
    text_type = unicode
else:
    text_type = str

# Run 2to3 tool
# python -m lib2to3 --write --nobackups src/

兼容层

# Adapter for API changes
class CompatibilityAdapter:
    def __init__(self, new_service):
        self.new = new_service

    # Old API signature
    def get_user(self, user_id):
        # Translate to new API
        return self.new.fetch_user(id=user_id)

    # Deprecation warning
    def old_method(self):
        warnings.warn(
            "old_method is deprecated, use new_method instead",
            DeprecationWarning
        )
        return self.new.new_method()

示例

输入：“从 Express 迁移到 Fastify” **操作：**创建适配器层，逐步迁移路由，并在每个步骤进行测试

输入：“减少此模块中的技术债务” **操作：**先添加测试，再逐步重构，同时保持兼容性