Agent skill

backend-patterns

Production-grade backend patterns for Node.js, Python, Go, and Java/Spring frameworks

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npx add-skill https://github.com/pluginagentmarketplace/custom-plugin-api-design/tree/main/skills/backend-patterns

SKILL.md

Backend Patterns Skill

Purpose

Implement production-ready backend services with proper patterns.

Framework Selection

Language Framework Best For
Node.js Express Simple APIs, quick prototypes
Node.js NestJS Enterprise, TypeScript
Node.js Fastify High performance
Python FastAPI Modern async, auto-docs
Python Django Full-featured, admin
Go Gin Fast, middleware
Java Spring Boot Enterprise, ecosystem

Error Handling Pattern

typescript
// Error hierarchy
class AppError extends Error {
  constructor(
    public code: string,
    message: string,
    public status: number = 500,
  ) {
    super(message);
    this.name = this.constructor.name;
  }
}

class NotFoundError extends AppError {
  constructor(resource: string, id: string) {
    super('NOT_FOUND', `${resource} ${id} not found`, 404);
  }
}

class ValidationError extends AppError {
  constructor(public errors: { field: string; message: string }[]) {
    super('VALIDATION_ERROR', 'Validation failed', 400);
  }
}

// Global handler
app.use((err, req, res, next) => {
  if (err instanceof AppError) {
    return res.status(err.status).json({
      type: `https://api.example.com/errors/${err.code.toLowerCase()}`,
      title: err.message,
      status: err.status,
    });
  }
  logger.error(err);
  res.status(500).json({ title: 'Internal error', status: 500 });
});

Middleware Pattern

typescript
// Request ID middleware
const requestId = (req, res, next) => {
  req.id = req.headers['x-request-id'] || crypto.randomUUID();
  res.setHeader('X-Request-ID', req.id);
  next();
};

// Logging middleware
const requestLogger = (req, res, next) => {
  const start = Date.now();
  res.on('finish', () => {
    logger.info({
      method: req.method,
      path: req.path,
      status: res.statusCode,
      duration: Date.now() - start,
      requestId: req.id,
    });
  });
  next();
};

// Error boundary
const asyncHandler = (fn) => (req, res, next) => {
  Promise.resolve(fn(req, res, next)).catch(next);
};

Validation Pattern

typescript
import { z } from 'zod';

const CreateUserSchema = z.object({
  email: z.string().email(),
  name: z.string().min(1).max(100),
  password: z.string().min(12),
});

function validate(schema) {
  return (req, res, next) => {
    const result = schema.safeParse(req.body);
    if (!result.success) {
      throw new ValidationError(
        result.error.issues.map(i => ({
          field: i.path.join('.'),
          message: i.message,
        }))
      );
    }
    req.body = result.data;
    next();
  };
}

app.post('/users', validate(CreateUserSchema), createUser);

Graceful Shutdown

typescript
const server = app.listen(3000);

async function shutdown() {
  console.log('Shutting down...');

  // Stop accepting new connections
  server.close();

  // Close database connections
  await db.destroy();

  // Close Redis
  await redis.quit();

  process.exit(0);
}

process.on('SIGTERM', shutdown);
process.on('SIGINT', shutdown);

Unit Test Template

typescript
describe('Backend Pattern: Error Handling', () => {
  it('should return proper error response', async () => {
    const res = await request(app)
      .get('/users/invalid-id')
      .expect(404);

    expect(res.body).toMatchObject({
      type: expect.stringContaining('not-found'),
      status: 404,
    });
  });
});

Troubleshooting

Issue Cause Solution
Memory leak Event listeners Remove on cleanup
Connection timeout Pool exhausted Increase pool size
Unhandled rejection Missing catch Add async handler

Quality Checklist

  • Error handling standardized
  • Request logging enabled
  • Input validation implemented
  • Graceful shutdown configured
  • Health check endpoint

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