Backend Development Best Practices: DRY, SOLID, High Availability, and Design Patterns

The author, a senior backend engineer at Tencent Cloud, shares practical guidelines for writing clean, maintainable code and building reliable backend systems.

1. Code Design Principles

DRY (Don’t Repeat Yourself) – avoid duplicated logic, semantics, or execution. Consolidate repeated code into reusable functions or classes.

class Calculator:
    def add(self, a, b):
        return a + b
    def subtract(self, a, b):
        return a - b
    def multiply(self, a, b):
        return a * b
    def divide(self, a, b):
        if b == 0:
            # ...throw DivideByZeroException...
            pass
        return a / b

class AdvancedCalculator(Calculator):
    def power(self, a, b):
        result = 1
        for _ in range(b):
            result *= a
        return result
    def square_root(self, a):
        if a < 0:
            # ...throw InvalidInputException...
            pass
        return math.sqrt(a)

Functional duplication (e.g., two functions that compute a square in different ways) should be abstracted into a single utility.

def square1(x):
    return x ** 2

def square2(x):
    return pow(x, 2)

def square(x):
    return x ** 2

2. SOLID Principles

Single Responsibility Principle (SRP) – a class should have only one reason to change. Separate responsibilities into distinct classes or modules.

Open‑Closed Principle (OCP) – software entities should be open for extension but closed for modification. Use abstract base classes or interfaces to add new behavior without altering existing code.

Liskov Substitution Principle (LSP) – subclasses must be substitutable for their base classes without breaking correctness.

class Shape:
    def area(self):
        pass

class Rectangle(Shape):
    def __init__(self, width, height):
        self.width = width
        self.height = height
    def area(self):
        return self.width * self.height

class Circle(Shape):
    def __init__(self, radius):
        self.radius = radius
    def area(self):
        return math.pi * self.radius ** 2

Interface Segregation Principle (ISP) – clients should not be forced to depend on interfaces they do not use. Split large interfaces into smaller, role‑specific ones.

Dependency Inversion Principle (DIP) – high‑level modules should depend on abstractions, not concrete implementations. Define abstract interfaces and let low‑level modules implement them.

3. Design Patterns

The article lists common patterns (creational, structural, behavioral) such as Singleton, Factory Method, Abstract Factory, Builder, Prototype, Adapter, Bridge, Composite, Decorator, Facade, Flyweight, Proxy, Chain of Responsibility, Command, Interpreter, Iterator, Mediator, Memento, Observer, State, Strategy, Template Method, Visitor.

4. High‑Availability Design

Key aspects include load balancing, clustering, distributed architecture, multi‑region deployment, comprehensive logging and monitoring (service‑level and business‑level), and disaster‑recovery planning. Reducing single points of failure and ensuring system stability are emphasized.

5. Automation and Efficiency

Automate repetitive workflows, use templates and standardized processes, and adopt project‑management tools to eliminate manual, error‑prone steps.

6. Value‑Driven Development

Focus on delivering user and business value. Question whether a task is truly important before investing effort.

7. Communication & Collaboration

Effective communication with product managers, teammates, and customers is essential for understanding requirements, coordinating work, and resolving issues.

8. Reliability & Responsibility

Maintain system reliability through thorough testing, clear ownership, and prompt feedback. Treat every task with a sense of responsibility.

9. Career Development

Encourage continuous learning, horizontal skill expansion, and soft‑skill improvement (communication, teamwork, leadership). Emphasize that developers should be lifelong learners to stay competitive.