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Original

English
🇨🇳

Translation

Chinese

Legacy Modernization

遗留系统现代化

Safely upgrade and modernize legacy systems.
安全地升级和现代化遗留系统。

When to Use

适用场景

  • Framework migrations
  • Language version upgrades
  • Monolith decomposition
  • Technical debt reduction
  • Dependency updates
  • 框架迁移
  • 语言版本升级
  • 单体应用拆分
  • 技术债务削减
  • 依赖项更新

Migration Strategies

迁移策略

Strangler Fig Pattern

绞杀者模式

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

1. Route new features to new service
2. Gradually migrate existing features
3. Eventually retire legacy system
┌─────────────────────────────────────┐
│           Load Balancer             │
└──────────────┬──────────────────────┘
               │
       ┌───────┴───────┐
       │               │
┌──────▼──────┐ ┌──────▼──────┐
│   Legacy    │ │    New      │
│   System    │ │   Service   │
└─────────────┘ └─────────────┘

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

Branch by Abstraction

抽象分支模式

python
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python
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1. Create abstraction layer

1. Create abstraction layer

class PaymentProcessor(ABC): @abstractmethod def process(self, amount: float) -> bool: pass
class PaymentProcessor(ABC): @abstractmethod def process(self, amount: float) -> bool: pass

2. Wrap legacy implementation

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)
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

3. Create new implementation

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

4. Use feature flag to switch

4. Use feature flag to switch

processor = (ModernPaymentProcessor() if feature_flag("new_payment") else LegacyPaymentProcessor(legacy))
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processor = (ModernPaymentProcessor() if feature_flag("new_payment") else LegacyPaymentProcessor(legacy))
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Migration Checklist

迁移检查清单

Before Starting

开始前

  • Document current behavior
  • Add tests for existing functionality
  • Set up monitoring and alerts
  • Create rollback plan
  • Communicate with stakeholders
  • 记录当前系统行为
  • 为现有功能添加测试
  • 配置监控与告警
  • 制定回滚计划
  • 与相关人员沟通

During Migration

迁移中

  • Make incremental changes
  • Test after each change
  • Monitor error rates
  • Keep legacy running in parallel
  • Document breaking changes
  • 进行增量式修改
  • 每次修改后执行测试
  • 监控错误率
  • 保持遗留系统并行运行
  • 记录破坏性变更

After Migration

迁移后

  • Remove feature flags
  • Clean up legacy code
  • Update documentation
  • Archive old codebase
  • Post-mortem lessons learned
  • 移除功能开关
  • 清理遗留代码
  • 更新文档
  • 归档旧代码库
  • 总结迁移经验教训

Common Migrations

常见迁移场景

jQuery to React

从jQuery迁移到React

javascript
// 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
javascript
// 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

Python 2 to 3

从Python 2迁移到Python 3

python
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python
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Use future imports for compatibility

Use future imports for compatibility

from future import print_function, division, absolute_import
from future import print_function, division, absolute_import

Use six for cross-version compatibility

Use six for cross-version compatibility

import six if six.PY2: text_type = unicode else: text_type = str
import six if six.PY2: text_type = unicode else: text_type = str

Run 2to3 tool

Run 2to3 tool

python -m lib2to3 --write --nobackups src/

python -m lib2to3 --write --nobackups src/

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Compatibility Layers

兼容层

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python
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Adapter for API changes

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()
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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()
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Examples

示例

Input: "Migrate from Express to Fastify" Action: Create adapter layer, migrate routes incrementally, test each step
Input: "Reduce technical debt in this module" Action: Add tests first, refactor incrementally, maintain compatibility
输入： "从Express迁移到Fastify" 操作： 创建适配层，逐步迁移路由，每一步都进行测试
输入： "削减该模块的技术债务" 操作： 先添加测试，逐步重构，保持兼容性