Senior Backend Engineer

Backend development patterns, API design, database optimization, and security practices.

Table of Contents

• Quick Start

• Tools Overview

• API Scaffolder

• Database Migration Tool

• API Load Tester

• Backend Development Workflows

• API Design Workflow

• Database Optimization Workflow

• Security Hardening Workflow

• Reference Documentation

• Common Patterns Quick Reference

Quick Start

Generate API routes from OpenAPI spec

python scripts/api_scaffolder.py openapi.yaml --framework express --output src/routes/

Analyze database schema and generate migrations

python scripts/database_migration_tool.py --connection postgres://localhost/mydb --analyze

Load test an API endpoint

python scripts/api_load_tester.py https://api.example.com/users --concurrency 50 --duration 30

Tools Overview

1. API Scaffolder

Generates API route handlers, middleware, and OpenAPI specifications from schema definitions.

Input: OpenAPI spec (YAML/JSON) or database schema Output: Route handlers, validation middleware, TypeScript types

Usage:

Generate Express routes from OpenAPI spec

python scripts/api_scaffolder.py openapi.yaml --framework express --output src/routes/

Output:

Generated 12 route handlers in src/routes/

- GET /users (listUsers)

- POST /users (createUser)

- GET /users/{id} (getUser)

- PUT /users/{id} (updateUser)

- DELETE /users/{id} (deleteUser)

...

Created validation middleware: src/middleware/validators.ts

Created TypeScript types: src/types/api.ts

Generate from database schema

python scripts/api_scaffolder.py --from-db postgres://localhost/mydb --output src/routes/

Generate OpenAPI spec from existing routes

python scripts/api_scaffolder.py src/routes/ --generate-spec --output openapi.yaml

Supported Frameworks:

• Express.js (--framework express )

• Fastify (--framework fastify )

• Koa (--framework koa )

2. Database Migration Tool

Analyzes database schemas, detects changes, and generates migration files with rollback support.

Input: Database connection string or schema files Output: Migration files, schema diff report, optimization suggestions

Usage:

Analyze current schema and suggest optimizations

python scripts/database_migration_tool.py --connection postgres://localhost/mydb --analyze

Output:

=== Database Analysis Report ===

Tables: 24

Total rows: 1,247,832

MISSING INDEXES (5 found):

orders.user_id - 847ms avg query time, ADD INDEX recommended

products.category_id - 234ms avg query time, ADD INDEX recommended

N+1 QUERY RISKS (3 found):

users -> orders relationship (no eager loading)

SUGGESTED MIGRATIONS:

1. Add index on orders(user_id)

2. Add index on products(category_id)

3. Add composite index on order_items(order_id, product_id)

Generate migration from schema diff

python scripts/database_migration_tool.py --connection postgres://localhost/mydb
--compare schema/v2.sql --output migrations/

Output:

Generated migration: migrations/20240115_add_user_indexes.sql

Generated rollback: migrations/20240115_add_user_indexes_rollback.sql

Dry-run a migration

python scripts/database_migration_tool.py --connection postgres://localhost/mydb
--migrate migrations/20240115_add_user_indexes.sql --dry-run

3. API Load Tester

Performs HTTP load testing with configurable concurrency, measuring latency percentiles and throughput.

Input: API endpoint URL and test configuration Output: Performance report with latency distribution, error rates, throughput metrics

Usage:

Basic load test

python scripts/api_load_tester.py https://api.example.com/users --concurrency 50 --duration 30

Output:

=== Load Test Results ===

Target: https://api.example.com/users

Duration: 30s | Concurrency: 50

THROUGHPUT:

Total requests: 15,247

Requests/sec: 508.2

Successful: 15,102 (99.0%)

Failed: 145 (1.0%)

LATENCY (ms):

Min: 12

Avg: 89

P50: 67

P95: 198

P99: 423

Max: 1,247

ERRORS:

Connection timeout: 89

HTTP 503: 56

RECOMMENDATION: P99 latency (423ms) exceeds 200ms target.

Consider: connection pooling, query optimization, or horizontal scaling.

Test with custom headers and body

python scripts/api_load_tester.py https://api.example.com/orders
--method POST
--header "Authorization: Bearer token123"
--body '{"product_id": 1, "quantity": 2}'
--concurrency 100
--duration 60

Compare two endpoints

python scripts/api_load_tester.py https://api.example.com/v1/users https://api.example.com/v2/users
--compare --concurrency 50 --duration 30

Backend Development Workflows

API Design Workflow

Use when designing a new API or refactoring existing endpoints.

Step 1: Define resources and operations

openapi.yaml

openapi: 3.0.3 info: title: User Service API version: 1.0.0 paths: /users: get: summary: List users parameters: - name: limit in: query schema: type: integer default: 20 post: summary: Create user requestBody: required: true content: application/json: schema: $ref: '#/components/schemas/CreateUser'

Step 2: Generate route scaffolding

python scripts/api_scaffolder.py openapi.yaml --framework express --output src/routes/

Step 3: Implement business logic

// src/routes/users.ts (generated, then customized) export const createUser = async (req: Request, res: Response) => { const { email, name } = req.body;

// Add business logic const user = await userService.create({ email, name });

res.status(201).json(user); };

Step 4: Add validation middleware

Validation is auto-generated from OpenAPI schema

src/middleware/validators.ts includes:

- Request body validation

- Query parameter validation

- Path parameter validation

Step 5: Generate updated OpenAPI spec

python scripts/api_scaffolder.py src/routes/ --generate-spec --output openapi.yaml

Database Optimization Workflow

Use when queries are slow or database performance needs improvement.

Step 1: Analyze current performance

python scripts/database_migration_tool.py --connection $DATABASE_URL --analyze

Step 2: Identify slow queries

-- Check query execution plans EXPLAIN ANALYZE SELECT * FROM orders WHERE user_id = 123 ORDER BY created_at DESC LIMIT 10;

-- Look for: Seq Scan (bad), Index Scan (good)

Step 3: Generate index migrations

python scripts/database_migration_tool.py --connection $DATABASE_URL
--suggest-indexes --output migrations/

Step 4: Test migration (dry-run)

python scripts/database_migration_tool.py --connection $DATABASE_URL
--migrate migrations/add_indexes.sql --dry-run

Step 5: Apply and verify

Apply migration

python scripts/database_migration_tool.py --connection $DATABASE_URL
--migrate migrations/add_indexes.sql

Verify improvement

python scripts/database_migration_tool.py --connection $DATABASE_URL --analyze

Security Hardening Workflow

Use when preparing an API for production or after a security review.

Step 1: Review authentication setup

// Verify JWT configuration const jwtConfig = { secret: process.env.JWT_SECRET, // Must be from env, never hardcoded expiresIn: '1h', // Short-lived tokens algorithm: 'RS256' // Prefer asymmetric };

Step 2: Add rate limiting

import rateLimit from 'express-rate-limit';

const apiLimiter = rateLimit({ windowMs: 15 * 60 * 1000, // 15 minutes max: 100, // 100 requests per window standardHeaders: true, legacyHeaders: false, });

app.use('/api/', apiLimiter);

Step 3: Validate all inputs

import { z } from 'zod';

const CreateUserSchema = z.object({ email: z.string().email().max(255), name: z.string().min(1).max(100), age: z.number().int().positive().optional() });

// Use in route handler const data = CreateUserSchema.parse(req.body);

Step 4: Load test with attack patterns

Test rate limiting

python scripts/api_load_tester.py https://api.example.com/login
--concurrency 200 --duration 10 --expect-rate-limit

Test input validation

python scripts/api_load_tester.py https://api.example.com/users
--method POST
--body '{"email": "not-an-email"}'
--expect-status 400

Step 5: Review security headers

import helmet from 'helmet';

app.use(helmet({ contentSecurityPolicy: true, crossOriginEmbedderPolicy: true, crossOriginOpenerPolicy: true, crossOriginResourcePolicy: true, hsts: { maxAge: 31536000, includeSubDomains: true }, }));

Reference Documentation

File Contains Use When

references/api_design_patterns.md

REST vs GraphQL, versioning, error handling, pagination Designing new APIs

references/database_optimization_guide.md

Indexing strategies, query optimization, N+1 solutions Fixing slow queries

references/backend_security_practices.md

OWASP Top 10, auth patterns, input validation Security hardening

Common Patterns Quick Reference

REST API Response Format

{ "data": { "id": 1, "name": "John" }, "meta": { "requestId": "abc-123" } }

Error Response Format

{ "error": { "code": "VALIDATION_ERROR", "message": "Invalid email format", "details": [{ "field": "email", "message": "must be valid email" }] }, "meta": { "requestId": "abc-123" } }

HTTP Status Codes

Code Use Case

200 Success (GET, PUT, PATCH)

201 Created (POST)

204 No Content (DELETE)

400 Validation error

401 Authentication required

403 Permission denied

404 Resource not found

429 Rate limit exceeded

500 Internal server error

Database Index Strategy

-- Single column (equality lookups) CREATE INDEX idx_users_email ON users(email);

-- Composite (multi-column queries) CREATE INDEX idx_orders_user_status ON orders(user_id, status);

-- Partial (filtered queries) CREATE INDEX idx_orders_active ON orders(created_at) WHERE status = 'active';

-- Covering (avoid table lookup) CREATE INDEX idx_users_email_name ON users(email) INCLUDE (name);

Common Commands

API Development

python scripts/api_scaffolder.py openapi.yaml --framework express python scripts/api_scaffolder.py src/routes/ --generate-spec

Database Operations

python scripts/database_migration_tool.py --connection $DATABASE_URL --analyze python scripts/database_migration_tool.py --connection $DATABASE_URL --migrate file.sql

Performance Testing

python scripts/api_load_tester.py https://api.example.com/endpoint --concurrency 50 python scripts/api_load_tester.py https://api.example.com/endpoint --compare baseline.json