In today’s digital landscape, building secure, scalable, and high-performance backend systems is crucial. Whether you're working with .NET Core, Node.js, or deploying APIs in the cloud, a solid foundation in REST API design, encryption, and DevOps practices is essential.
This article covers essential interview-level knowledge and practical implementation techniques for backend developers working across .NET, Node.js, cryptography, cloud security, and API design. It concludes with hands-on tasks to evaluate readiness in real-world scenarios.
.NET (C#) Development Essentials
- .NET Core vs. .NET Framework
- .NET Core: Cross-platform, open-source, ideal for microservices and modern applications.
- .NET Framework: Windows-only, better suited for legacy enterprise apps.
- Dependency Injection in .NET Core: Leverage IServiceCollection in Startup.cs using methods like AddSingleton, AddScoped, and AddTransient.
- Building REST APIs with ASP.NET Core
- Use controllers, define [HttpGet], [HttpPost] routes.
- Return ActionResult<T> and inject dependencies via constructor injection.
- Async/Await for Scalability
- Enables non-blocking I/O operations.
- Crucial for handling concurrent requests with fewer threads.
- Exception Handling in Web APIs: Use try/catch blocks, custom middleware, and return meaningful HTTP status codes.
- Securing API Endpoints: Implement JWT or OAuth2, enable HTTPS, validate input, and use [Authorize].
- HttpClient Usage: Prefer IHttpClientFactory to prevent socket exhaustion and centralize configuration.
Node.js Development Essentials
- Asynchronous Operations & Event Loop: Single-threaded event loop with async callbacks handles concurrency efficiently.
- Streams: Handle data in chunks for memory efficiency. Useful in file processing and large payload APIs.
- Securing Express.js APIs: Use helmet, JWT, input sanitization, HTTPS, and validation.
- Environment Variables & Secrets: Use .env and dotenv. In production, integrate secret managers like AWS Secrets Manager.
- Middleware in Express.js: Use app.use() to inject logging and authentication logic.
Cryptography & Secure Data Handling
- Symmetric vs. Asymmetric Encryption
- Symmetric: Same key for encryption/decryption.
- Asymmetric: Public/private key pair (e.g., RSA).
- RSA & ECC
- RSA: Widely used for secure communication.
- ECC: Smaller keys, faster, same security level as RSA.
- SHA-256 Hashing: Used for password hashing and data integrity checks.
- Digital Signatures: Sign with private key, verify with public. Ensures authenticity and integrity.
- Certificate Storage: Use secure storage (Azure Key Vault, AWS Secrets Manager). Avoid hard-coding.
- Key Rotation: Maintain backward compatibility temporarily. Monitor, then remove old keys.
- Preventing MITM Attacks: Use HTTPS, enforce HSTS, and validate certificates.
Secure Token Handling & Certificate Management
- JWT Structure & Verification
- Consists of: Header, Payload, and Signature.
- Verify using public key or shared secret.
- OAuth 2.0 vs OpenID Connect
- OAuth: Authorization protocol.
- OpenID Connect: Extends OAuth to include authentication.
- Token Issuance in Distributed Systems: Use a trusted token authority. Sign tokens securely and manage expiration.
- Certificate Signing & Trust Chain: CA-signed certificates are trusted by clients. Self-signed certificates are not.
- Managing Private Keys in Cloud: Store in secure services and use managed identities.
Cloud & DevOps Best Practices
- Secrets & Certificate Management
- Use Azure Key Vault or AWS Secrets Manager.
- Avoid storing secrets in source control.
- CI/CD Deployments: Automate builds/tests using GitHub Actions, Azure DevOps, or AWS CodePipeline.
- CI/CD Security: Scan code, restrict access, use signed build artifacts.
- Monitoring & Logging: Use Azure Monitor, AWS CloudWatch, ELK, or Datadog.
REST API Design & Security
- REST Principles: Statelessness, resource-based URIs, and correct HTTP verbs.
- Security Best Practices: Enforce HTTPS, validate inputs, use tokens, and avoid sensitive data in URLs.
- API Versioning: Common practice: /api/v1/resource or use custom headers.
- HTTP Status Codes: 401 Unauthorized, 404 Not Found, 400 Bad Request, 204 No Content.
- Rate Limiting & Abuse Prevention: Use middleware or external tools like NGINX or Redis for token buckets.
System Design Scenarios
- Secure Digital Pass System: Issue JWTs with expiration. Maintain a revocation list or blacklist.
- Certificate Generation Microservice: Stateless service, secure key handling, async job queue, audit logs.
- Secure Mobile/Web Backend Architecture: Use REST APIs + HTTPS + token auth. Separate identity and data APIs.
Bonus: Hands-On Tasks
.NET API with JWT Auth
services.AddAuthentication(JwtBearerDefaults.AuthenticationScheme)
.AddJwtBearer(options => { /* token validation config */ });
Node.js RSA Encryption
const { generateKeyPairSync, publicEncrypt, privateDecrypt } = require('crypto');
const { publicKey, privateKey } = generateKeyPairSync('rsa', { modulusLength: 2048 });
const encrypted = publicEncrypt(publicKey, Buffer.from("secret"));
const decrypted = privateDecrypt(privateKey, encrypted);
.PFX in Azure Key Vault
- Upload via Azure Portal or CLI.
- Access with Azure.Security.KeyVault.Certificates.
CI/CD with GitHub Actions
jobs:
build:
runs-on: ubuntu-latest
steps:
- uses: actions/checkout@v2
- name: Setup .NET
uses: actions/setup-dotnet@v3
with:
dotnet-version: '7.0.x'
- run: dotnet build
- run: dotnet test
Conclusion
This article is a compact yet powerful reference for backend engineers preparing for interviews or looking to enhance their expertise in secure backend development. From foundational principles to real-world scenarios, it bridges theory and practice in modern backend engineering.
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