Backend Concepts

Elasticsearch is a distributed search and analytics engine built on Lucene, excelling at full-text search, aggregations, and real-time indexing for logs/apps. Part of ELK stack.

An Event Bus is a pub/sub pattern for loose coupling, where producers emit events and consumers subscribe to topics for async communication. Implemented with libraries like EventEmitter or Redis Pub/Sub.

Apache Kafka is a distributed event streaming platform for high-throughput, fault-tolerant pub/sub messaging, used for data pipelines and real-time processing. It stores streams durably with partitions for scalability.

A Circuit Breaker is a design pattern that prevents cascading failures in distributed systems by detecting when a service is not responding and stopping requests to it temporarily. It "trips" the circuit to fallback mode after failures, allowing recovery time.

RabbitMQ is a message broker implementing AMQP for reliable queuing, routing, and delivery in distributed systems. Supports plugins for MQTT, STOMP.

An API Gateway acts as a single entry point for multiple backend services, handling routing, authentication, rate limiting, and other cross-cutting concerns. It simplifies microservices architecture by abstracting service discovery and load balancing.

GraphQL is a query language for APIs allowing clients to request exact data needed, reducing over/under-fetching with a schema-driven approach. It supports subscriptions for real-time updates.

A Session Manager handles user sessions server-side, storing state in memory, databases, or Redis for secure, stateful authentication across requests. It manages creation, validation, and expiration with CSRF protection.

Laravel is an elegant PHP framework for web apps, with Eloquent ORM, Blade templating, queues, and Artisan CLI for productive development. Known for expressive syntax.

NestJS is a progressive Node.js framework for building efficient, scalable server-side apps using TypeScript, inspired by Angular with modules, decorators, and DI. It supports GraphQL, WebSockets, and microservices.

Spring Boot simplifies Java app dev with auto-config, embedded servers, and starters for microservices, REST, security. Part of Spring ecosystem.

A Background Job Worker processes asynchronous tasks like email sending or data imports off the main request thread, using queues like Bull or Sidekiq for reliability. It ensures non-blocking UIs and fault-tolerant execution.

A Message Queue Module decouples producers/consumers with FIFO storage, retries, and priorities for async task distribution. Uses RabbitMQ/SQS.

A Webhook Handler Module receives and verifies incoming HTTP POSTs from services (e.g., Stripe, GitHub), with signatures, retries, and queuing for reliability. Async processing.

A Search Module implements full-text or fuzzy search using algos like BM25 or vector embeddings, with filters and facets for e-comm/sites. Integrates Elasticsearch or DB native.

Edge Middleware runs code at CDN edge before requests reach origin, for auth, rewrites, A/B, headers. Low latency, stateless.

A Vector Database stores and queries high-dimensional embeddings for similarity search, powering AI features like semantic search or recommendations. Examples: Pinecone, Weaviate, Milvus.

Hono is a lightweight, ultrafast web framework for Cloudflare Workers and other runtimes, emphasizing simplicity with middleware support and JSX rendering. It's designed for edge computing with minimal overhead.

LangChain is a framework for LLM apps, chaining prompts, agents, tools, memory for complex workflows like chatbots or RAG. JS/Python.

LlamaIndex (formerly GPT Index) is a framework for building LLM-powered apps, focusing on data ingestion, indexing, and retrieval for RAG (Retrieval-Augmented Generation). It connects LLMs to custom data sources like PDFs or databases.

A Rate Limiter Module throttles requests per IP/user to prevent abuse, DDoS, using token bucket or sliding window algos with Redis storage. Enforces API quotas.

A Logging Module captures application events, errors, and metrics in structured formats, forwarding to sinks like ELK or Splunk for analysis and alerting. It supports levels (debug, info, error) and context enrichment.

A File Upload Module handles multipart form data, validation, storage (local/S3), and resizing for secure, efficient file handling in web apps. It often uses libraries like Multer or AWS SDK.

Express.js is a minimal Node.js web framework providing routing, middleware, and HTTP utilities for building APIs and servers with unopinionated flexibility. It's the backbone for many MEAN/MERN stacks.

Django is a high-level Python web framework promoting rapid development with "batteries-included" features like ORM, admin panel, and auth. It follows MVT architecture for scalable web apps.

An API Pagination Module implements cursor/offset/page-based splitting of large result sets to improve performance and UX. Supports links in headers for navigation.

An Authentication Module handles user identity verification, typically using JWT, OAuth, or sessions, integrated into backend frameworks for secure access control. It often includes registration, login, password reset, and role-based authorization.

A Caching Module stores frequently accessed data in fast-access layers like Redis or in-memory to reduce database load and improve response times. It implements strategies like LRU, TTL, and cache-aside patterns.

Redis is an in-memory data structure store used as DB, cache, MQ with strings, hashes, lists, sets supporting pub/sub and Lua scripts. High throughput.

FastAPI is a modern Python web framework for APIs, based on Starlette and Pydantic, emphasizing speed, async support, and auto-generated docs with OpenAPI. It's ideal for data/ML-heavy backends.