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🎯 Interview Prep

Comprehensive preparation for Senior / Staff / Principal backend engineering interviews
Also includes: Nginx internals • Compression (Gzip, Deflate, Zstd, Brotli) • Infrastructure tools

30 LLD Projects
190 DSA Questions
200+ Staff-Level Questions
8 CS Core Topics
📦 Explore Modules

🎯 Start Here: Follow This Order (Step 1 → 8)

New here? Read the Study Guide first: tracks by target role (Backend, Staff, AI/FDE, SRE) and by language background (Python, Java, Go, other).

Step 1 · FundamentalsCS CoreOS, networks, databases, distributed systems, concurrency, security. Step 2 · CodingDSA190 problems across 20 categories with thought process and complexity. Step 3 · Language depthGo · Python · JavaRuntime internals, concurrency, coding challenges, production patterns. Step 4 · Low-level designLLD30 projects in Python, Java and Go, plus the interview playbook. Step 5 · System designSystem Design45-minute framework, estimation cheat sheet, 8 end-to-end case studies. Step 6 · InfrastructureCloud & ToolsAWS, Kafka, Redis, Kubernetes, Postgres tooling, observability. Step 7 · AIAI EngineeringRAG, MCP, agents, LLM internals, production AI systems. Step 8 · LeadershipStaff CraftBehavioral stories, design docs and RFCs, reliability and incident leadership.

🧭 Skills Map

🟢 Beginner CS Fundamentals & OOD Basics
🖥️ Operating Systems Processes, memory, I/O, scheduling 📊 Data Structures Bloom filters, tries, sketches 🏗️ OOD Basics Parking Lot, Chess, Tic-Tac-Toe
🔵 Intermediate Concurrency, DB, Networks, Design Patterns
⚡ Concurrency Lock-free, memory models, RCU 🗄️ Database Systems MVCC, B-Tree vs LSM, sharding 🌐 Networks TCP, HTTP/2/3, QUIC, TLS 🛡️ API Design Rate limiter, pub-sub, caching
🟣 Advanced Distributed Systems, Architecture, Security
🌍 Distributed Systems Raft, Paxos, CRDTs, gossip 🏛️ Architecture CQRS, event sourcing, DDD 🔒 Security JWT, OAuth2, OWASP, encryption 💳 Payments & ATMs Idempotency, circuit breaker
🔴 Staff/Principal Language Internals, RAG, Production Systems
🐍 Python Internals GIL, async, metaclasses, C extensions 12 questions + concurrency 🎯 Django Deep-Dive ORM internals, DRF, Celery, CQRS, multi-tenancy 16 questions 🐹 Go Internals GMP scheduler, GC, channels, sync 12 questions + concurrency 📚 RAG & LLMs Retrieval, embeddings, fine-tuning 7 guides 🔧 Harness & Loop Eng Scaffolding, guardrails, agent loops 2 guides

This roadmap outlines the optimal order to study for Staff/Principal backend engineering interviews. Follow the phases in sequence — each builds on the previous.

Phase 1: CS Fundamentals (2-3 weeks)

# Topic Why Resources
1 Operating Systems Foundation: processes, memory, scheduling, I/O OS Questions
2 Computer Networks TCP/IP, HTTP/2/3, TLS, QUIC, load balancing Networks Questions
3 Data Structures & Algorithms Bloom filters, tries, sketches, LRU cache DSA Questions + Scale DSA
4 Database Systems MVCC, B-Tree vs LSM, indexes, sharding, replication DB Questions

Phase 2: Language Deep-Dives (2-3 weeks — pick your stack)

# Topic Why Resources
5 Python GIL, async/await, metaclasses, C extensions Python Q&A + Async
5 Golang (alternative) GMP scheduler, GC, channels, interfaces Go Q&A + Concurrency + Coding Challenges + Production
5 Java (alternative) JVM internals, GC tuning, Spring Boot Java Q&A + JVM

Phase 3: Low-Level Design (3-4 weeks)

| # | Project | Skills Built | Resources | | 6 | Parking Lot | OOD basics, SOLID, Strategy/Factory patterns | Code | | 7 | Vending Machine | State machines, finite automata | Code | | 8 | LRU Cache / Rate Limiter | Data structures, concurrency | Cache + Rate Limiter | | 9 | Pub-Sub / Movie Booking | Observer pattern, concurrency control | Pub-Sub + Booking | | 10 | Splitwise / Library Mgmt | Graph algorithms, facade pattern | Splitwise + Library | | 11 | Cab Booking / Car Rental | Geo queries, Kafka integration, availability | Cab + Car Rental | | 12 | ATM / Payment Processing | State machines, fraud detection, idempotency | ATM + Payments | | 13 | Chess Game | Complex state, enums, validation | Chess | | 14 | Notification Service | High-throughput, multi-channel, cost-effective, scheduling | HLD + Code | | 15 | Job Scheduling (Airflow-like) | Core-aware scheduling, DAG, recurring jobs, cron | Design | | 16 | Search Platform | TF-IDF, inverted index, ranking | Search | | 17 | Elevator System | State machine, dispatching, SCAN algorithm | Java Code | | 18 | Hotel Booking | Inventory, pricing, reservations | Java Code | | 19 | Meeting Scheduler | Calendar, conflict detection, rooms | Java Code | | 20 | Web Crawler | Concurrency, worker pool, rate limiting | Go Code | | 21 | KV Store | TTL, eviction policies, snapshots | Go Code | | 22 | Task Queue | Priority queue, retry, graceful shutdown | Go Code | | 23 | Circuit Breaker / Logging Framework | Resilience state machines, async bounded queues | Breaker + Logger | | 24 | Food Delivery / Order Matching Engine | Sagas, dispatch without double-assignment, single-writer sequencing | Food Delivery + Matching Engine |

Phase 4: Distributed Systems & Architecture (2-3 weeks)

# Topic Why Resources
17 Distributed Systems Raft, Paxos, CRDTs, gossip, CAP theorem DS Questions + Transactions
18 Concurrency & Parallelism Lock-free, race conditions, memory models Concurrency Q&A
19 Software Architecture CQRS, event sourcing, DDD, microservices Architecture Q&A + Patterns
20 Security JWT, OAuth2, OWASP, encryption, SSRF Security Q&A

Phase 5: AI Engineering (2-3 weeks — high growth area)

# Topic Why Resources
21 RAG Fundamentals Understand retrieval-augmented generation RAG Overview
22 RAG Implementation ChromaDB, embeddings, FastAPI RAG Code
23 MCP Protocol Model Context Protocol, server/client MCP Fundamentals + Servers
24 Agent Fundamentals ReAct, Plan-and-Execute, memory systems Agent Fundamentals
25 LangGraph Graph-based state machines for agents LangGraph Notes
26 Multi-LLM Architecture Routing, cost management, fallback across GPT/Claude/DeepSeek Multi-LLM Design
27 Agent Observability Monitoring, debugging, proactive alerts, data policies Observability
28 Redis Lease Distributed locking with Redis TTL Redis Lease
29 Search Autocorrect Misspelling handling, Levenshtein, Soundex, BK-tree Search Autocorrect
30 Elasticsearch Internals Inverted index, BM25, analysis pipeline, sharding Elasticsearch
31 Agent Deployment (ECS) Production infra, ECS, API flow, monitoring, cost Deployment Guide
32 Agent Interview Prep Staff-level agent questions and answers Agent Q&A
33 Harness Engineering Evaluation/agent harnesses, guardrails, sandboxing, verification Harness Engineering
34 Loop Engineering Agentic loops, ReAct, feedback cycles, termination logic Loop Engineering

💡 Tip: Phase 5 is dense. Focus on RAG → Agent Fundamentals → LangGraph → Multi-LLM → Harness & Loop first if time is limited. Deployment and observability can be studied after the core concepts.

Phase 6: Cloud & Tools (1-2 weeks)

# Topic Why Resources
33 AWS Compute, networking, storage, messaging, security AWS Overview
34 Kafka Event streaming, partitioning, replication, exactly-once Kafka Q&A
35 Redis Caching, distributed locks, data structures, persistence Redis Q&A
36 Elasticsearch Inverted index, BM25, analysis pipeline, sharding ES Q&A
37 Docker Container runtime, namespaces, cgroups, image layering, multi-stage builds Docker Q&A
38 Kubernetes Orchestration, scheduling, networking, RBAC, storage, production ops K8s Q&A + Pod Lifecycle + Production Control + Versioning
38 Monitoring & Infra Prometheus, Grafana, Terraform Prometheus + Terraform
39 Nginx & Compression Reverse proxy, load balancing, Gzip/Zstd/Brotli Nginx + Compression

📊 Estimated Timeline

Phase Duration Focus
Phase 1 2-3 weeks CS Fundamentals — build the base
Phase 2 2-3 weeks Language Deep-Dive — master your stack
Phase 3 3-4 weeks Low-Level Design — 30 projects
Phase 4 2-3 weeks Distributed Systems — think at scale
Phase 5 2-3 weeks AI Engineering — emerging hot topic
Phase 6 1-2 weeks Cloud & Tools — fill gaps
Total 13-20 weeks Full interview preparation

💡 Study Tips

  • Don't jump ahead — Phase 1 fundamentals are asked in EVERY interview
  • Pick ONE language for Phase 2 (the one you'll interview in)
  • Build, don't just read — run the code for every LLD project
  • Focus Phase 5 — AI agent questions are increasingly common at Staff/Principal level
  • The rubric matters — each question has an evaluation table showing what interviewers expect
  • Use search — press Ctrl+K / Cmd+K on desktop, or tap the 🔍 search icon in the header on mobile

📦 Modules Overview

🐍 Python LLD
24 projects SOLID design patterns, Python implementations, HLD architecture docs. Parking Lot → Order Matching Engine.
OOD SOLID Patterns
☕ Java LLD
3 projects Elevator System, Hotel Booking, Meeting Scheduler. OOP with Strategy, State, Observer patterns.
Java OOP Patterns
🦦 Go LLD
3 projects Web Crawler, KV Store, Task Queue. Concurrency with goroutines, channels, worker pools.
Go CSP goroutines
🧠 AI Engineering
4 modules + code RAG chatbot, MCP protocol, AI agents, Harness & Loop engineering. From fundamentals to production deployment.
RAG MCP Agents FastAPI
🐍 Python Deep-Dive
13 questions + 5 guides CPython internals: GIL, event loops, metaclasses, memory management. Includes multithreading notes with GIL workarounds, async patterns.
CPython GIL Async
🎯 Django Framework
16 questions ORM internals, DRF optimization, CQRS, multi-tenancy, Celery, caching strategies, zero-downtime migrations.
Web Staff DRF
🐹 Golang Deep-Dive
12 questions + guides Go runtime: GMP scheduler, GC, channels, interfaces, memory model. Includes concurrency notes, 7 tested coding challenges, language internals, and production HTTP/DB/profiling guides.
Runtime CSP Staff
🖥️ CS Core
8 topics OS, Networks, DB, Distributed Systems, Concurrency, DSA, Architecture, Security — 90+ questions.
Fundamentals Principal

🚀 How to Use This Site

🔍

Find Topics Fast

Press Ctrl+K / Cmd+K on desktop, or tap the 🔍 search icon in the header on mobile.

📖

Study Systematically

Follow the skills map from top to bottom. Start with CS fundamentals, then move to architecture.

💻

Run the Code

Every project has runnable Python code. Clone the repo and try each implementation.

📋

Check the Rubric

Each question has a Staff-Level Evaluation table showing what interviewers look for in answers.

🛠️ Technology Stack

🐍 Python 3.14+ All LLD implementations
🐹 Go Runtime deep-dive
🎨 MkDocs Material Documentation site
🧠 LangChain + ChromaDB RAG pipeline
⚡ FastAPI + Uvicorn RAG API server
🔤 sentence-transformers Embeddings

Built with ❤️ for backend engineers preparing for Senior/Staff/Principal-level interviews