Data and consistency
Start here for database indexes, transactions, locking, sharding, and eventual consistency.
Knowledge map
See how backend ideas connect.
Explore by domain and module when you need context, then enter a guided path when you are ready to study in sequence.
01
6 modules
System Design
Design reliable backend systems through data, traffic, async work, and failure trade-offs.
Database performance and operations
Diagnose query explosions, tune connection pools, plan migrations, and keep database-backed APIs stable.
Reliability and resilience
Learn how production systems handle dependency failures, retries, duplicate work, and overload.
Async processing
Understand queues, background jobs, webhooks, and the operational details behind async workflows.
Traffic and API architecture
Study how requests reach backend services and how public API contracts stay stable over time.
Additional guided lessons
Complete the course with focused guides that extend the core sequence.
02
6 modules
Java Collections
Choose Java collections by access pattern, correctness constraints, and performance behavior.
Map fundamentals
Start with HashMap behavior, TreeMap ordering, legacy Hashtable differences, load factor tuning, and concurrent map choices.
Equality and hashing
Understand equals, hashCode, key mutability, collision handling, and why hash-based collections behave the way they do.
Set choices
Compare hash-based uniqueness with sorted set behavior, range navigation, comparator rules, and membership checks.
List choices
Compare ArrayList and LinkedList through access patterns, insertion cost, memory overhead, and backend usage.
Queues and priority
Choose between FIFO queues, double-ended queues, heap-backed priority queues, and algorithmic top-K patterns.
Complexity and performance
Use Big-O as a practical language for collection choices, hot paths, memory overhead, and code reviews.
03
6 modules
API Design
Build clear API contracts that remain predictable through errors, retries, and change.
API style and contracts
Choose API style, review REST contracts, document schemas, evolve versions, and understand where an API gateway and browser preflight behavior fit.
Responses and errors
Design status codes, stable error shapes, request IDs, and client-friendly failure behavior.
Authentication and access
Protect APIs with authentication choices, cookies vs tokens, API keys, OAuth scopes, service credentials, gateways, and clear auth failures.
Reliability and retries
Make API retries safer with idempotency, abuse prevention, rate limits, backoff, and predictable response contracts.
Data and integrations
Handle paginated data, pagination metadata, webhook delivery, JSON contracts, schemas, and payload inspection.
Implementation and delivery
Connect API design decisions to a concrete Spring Boot controller implementation.
04
4 modules
Authentication
Understand identity, tokens, sessions, OAuth, and browser security boundaries.
Authentication architecture
Compare identity, credentials, permissions, sessions, JWTs, OAuth, OpenID Connect, and login tradeoffs.
- Password Hashing Explained for Backend Developers
- MFA Explained for Web Apps
- Authorization vs Authentication
- JWT vs Session Authentication: Practical Backend Tradeoffs
- Cookie vs Token Authentication
- OAuth 2.0 vs OpenID Connect
- OAuth 2.0 Explained for Backend Developers
- OAuth Scopes Explained
- OAuth Client Credentials Flow Explained
- Service Accounts Explained
Token lifecycle and claims
Understand access tokens, refresh tokens, API keys, JWT claims, expiration, rotation, and local inspection.
Browser security risks
Connect CORS, cookies, bearer tokens, CSRF, XSS, storage choices, session fixation, and safe browser authentication design.
Protected API behavior
Design permission checks, least privilege, authentication failures, gateway checks, OAuth resource servers, API keys, and clear API responses.
05
5 modules
Backend Security
Protect APIs, credentials, sessions, integrations, and operational trust boundaries.
Identity and access control
Separate identity, permissions, login state, delegated authorization, and protected resource checks.
- Password Hashing Explained for Backend Developers
- MFA Explained for Web Apps
- Authorization vs Authentication
- RBAC vs ABAC: Access Control Models Explained
- JWT vs Session Authentication: Practical Backend Tradeoffs
- OAuth 2.0 vs OpenID Connect
- OAuth 2.0 Explained for Backend Developers
- OAuth Scopes Explained
- OAuth Client Credentials Flow Explained
- Service Accounts Explained
- API Key vs OAuth Token: Practical Backend Differences
Token and session safety
Understand token claims, expiration, refresh behavior, local inspection, timestamps, and revocation tradeoffs.
Browser and cross-origin risks
Connect origins, credentials, cookie behavior, cookie hardening, preflight requests, CSRF, XSS, URL encoding, and browser-backed API calls.
Operational security
Use security event logs, audit logs, secret handling, service accounts, least privilege, and safe evidence trails to operate production systems.
Secure API behavior
Design gateway checks, rate limits, 401 and 403 responses, safe error messages, and useful debugging signals.
06
5 modules
Algorithms
Build practical complexity judgment for search, arrays, heaps, and backend code reviews.
Complexity fundamentals
Learn the growth curves behind common algorithms and use Big-O as a practical code review language.
Array and subarray patterns
Study sliding windows, two pointers, and prefix sums for common array, string, and range-query problems.
Search and sorted data
Understand binary search, sorted input requirements, logarithmic growth, and lookup tradeoffs.
Heaps and top K
Use heap-backed priority queues when ranking, scheduling, or keeping only the best K items.
Java collection choices
Connect algorithm complexity to everyday backend collection choices, maps, lists, queues, and sets.