Backend Study Lab · Games

Backend concept map

Use this map to connect games to the backend ideas they teach, then revisit weak concepts from your local review history.

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Concepts

Each concept links to games, learning objectives, common mistakes, and local review items.

All games by concept

The same 15 games are preserved; the concept map simply gives them a study structure.

Auth Intermediate

Auth Token Inspector

Inspect authentication scenarios and choose safe backend decisions for tokens, scopes, sessions, CSRF, and object-level authorization.

Time
6-9 minutes
Concept
Authentication, authorization, sessions, and token safety
  • Foundations
  • Auth
  • JWT
  • sessions
Play Auth Token Inspector
Algorithms Advanced

Bloom Filter Tuner

Tune Bloom-filter capacity, hash count, verification, saturation, and deletion behavior without introducing false negatives.

Time
8-11 minutes
Concept
Bloom filters and probabilistic membership
  • Algorithmic Reasoning
  • bloom filter
  • hashing
  • probability
Play Bloom Filter Tuner
Caching Beginner

Cache Eviction Lab

Predict cache hits and misses as requests flow through an LRU cache, then experiment with TTL behavior and stale data tradeoffs.

Time
5-8 minutes
Concept
Cache hits, misses, LRU, TTL, and stale data
  • Data & Performance
  • Algorithmic Reasoning
  • cache
  • LRU
  • TTL
Play Cache Eviction Lab
Reliability Intermediate

Circuit Breaker Clinic

Diagnose dependency failures and choose circuit breaker, timeout, fallback, retry, half-open, and bulkhead strategies that reduce blast radius.

Time
6-9 minutes
Concept
Circuit breakers, timeouts, retries, fallbacks, and dependency isolation
  • Production Reliability
  • resilience
  • circuit breaker
  • timeouts
Play Circuit Breaker Clinic
APIs Intermediate

CORS Preflight Pilot

Guide browser API requests through CORS decisions covering origins, preflight, credentials, exposed headers, and cache safety.

Time
6-9 minutes
Concept
CORS, browser security boundaries, and preflight response design
  • Foundations
  • CORS
  • HTTP
  • browser security
Play CORS Preflight Pilot
APIs Beginner

API Route Builder

Design REST-style methods and routes for product requirements such as creating users, updating email, searching products, and nested comments.

Time
6-9 minutes
Concept
REST API route design
  • Foundations
  • REST
  • API design
  • routes
Play API Route Builder
Databases Advanced

Deadlock Detective

Read waits-for cycles, choose safe victims, retry complete transactions, and prevent recurring deadlocks.

Time
7-11 minutes
Concept
Database deadlocks and lock ordering
  • Database Reliability
  • deadlocks
  • locks
  • transactions
Play Deadlock Detective
Async Reliability Advanced

DLQ Recovery Console

Classify failures, bound retries, quarantine poison messages, and replay dead-letter work with approval and idempotency.

Time
8-12 minutes
Concept
Dead-letter queue operations
  • Async Workflows
  • dlq
  • retries
  • operations
Play DLQ Recovery Console
Async Reliability Advanced

Delivery Guarantee Timeline

Trace producer, broker, consumer, acknowledgment, crash, and redelivery boundaries to name the real delivery guarantee.

Time
7-10 minutes
Concept
Message delivery semantics and acknowledgment timing
  • Async Workflows
  • delivery semantics
  • acknowledgments
  • retries
Play Delivery Guarantee Timeline
HTTP Caching Advanced

ETag & CDN Revalidation Lab

Follow validators through browser, CDN, and origin while handling 304 responses, representation variants, purge, and bounded staleness.

Time
8-12 minutes
Concept
Conditional requests and CDN cache operation
  • Data & Performance
  • etag
  • cdn
  • conditional requests
Play ETag & CDN Revalidation Lab
HTTP Caching Intermediate

HTTP Cache Policy Lab

Choose browser and shared-cache policies for public, personalized, validated, and variant API responses.

Time
7-10 minutes
Concept
HTTP cache policy and sensitive response boundaries
  • Data & Performance
  • http caching
  • cache-control
  • privacy
Play HTTP Cache Policy Lab
APIs Beginner

HTTP Status Defender

Choose the correct HTTP status code for realistic backend scenarios and learn the response semantics behind each answer.

Time
5-8 minutes
Concept
HTTP status codes and response semantics
  • Foundations
  • HTTP
  • REST
  • status codes
Play HTTP Status Defender
Reliability Intermediate

Idempotency Key Clinic

Diagnose retry scenarios and choose safe idempotency behavior for payments, emails, imports, orders, PUT updates, and scarce inventory.

Time
6-9 minutes
Concept
Idempotency, retries, duplicate prevention, and consistency
  • Production Reliability
  • Async Workflows
  • Idempotency
  • Reliability
  • Consistency
Play Idempotency Key Clinic
Async Reliability Advanced

Idempotent Consumer Lab

Build duplicate-safe consumers with scoped event identity, database constraints, and atomic business mutations.

Time
8-11 minutes
Concept
Idempotent message consumers
  • Async Workflows
  • idempotency
  • consumers
  • constraints
Play Idempotent Consumer Lab
Java Advanced

JVM Warmup & Capacity Lab

Measure JIT compilation, code cache, warmup, AOT training, and capacity with explicit guardrails and rollback.

Time
10-12 minutes
Concept
JVM Performance Diagnostics
  • JVM Performance Diagnostics
  • JVM
  • JIT
  • Warmup
Play JVM Warmup & Capacity Lab
Scaling Intermediate

Load Balancer Challenge

Route simulated traffic across backend servers using round robin, weighted round robin, least connections, and random strategies.

Time
6-10 minutes
Concept
Load balancing strategies
  • Production Reliability
  • load balancing
  • scaling
  • latency
Play Load Balancer Challenge
Queues Intermediate

Message Queue Simulator

Tune workers, retries, and dead-letter behavior while jobs move through an async queue with failures and poison messages.

Time
7-11 minutes
Concept
Async jobs, retries, visibility timeout, and dead-letter queues
  • Production Reliability
  • Async Workflows
  • queues
  • retries
  • dead-letter queue
Play Message Queue Simulator
Auth Advanced

OAuth Code Flow Debugger

Trace Authorization Code flow failures across state, PKCE, redirect URI, token exchange, and session boundaries.

Time
8-11 minutes
Concept
OAuth Authorization Code flow
  • Foundations
  • oauth
  • pkce
  • authentication
Play OAuth Code Flow Debugger
Async Reliability Advanced

Outbox Relay Recovery

Recover a transactional outbox relay across commit, publish-confirm, duplicate delivery, and poison-event failure windows.

Time
8-12 minutes
Concept
Transactional outbox and relay recovery
  • Async Workflows
  • outbox
  • transactions
  • messaging
Play Outbox Relay Recovery
Reliability Advanced

Overload Control Room

Control queue growth, adaptive concurrency, health probes, and priority-aware load shedding during overload.

Time
9-12 minutes
Concept
Backpressure and overload control
  • Production Reliability
  • Rate Limiting
  • Backpressure
  • Reliability
Play Overload Control Room
Reliability Intermediate

Observability Incident Triage

Triage production incidents by choosing useful metrics, logs, traces, queue signals, database evidence, request ids, and alerting strategies.

Time
6-9 minutes
Concept
Production observability, incident triage, metrics, logs, traces, and alerts
  • Production Reliability
  • observability
  • incidents
  • metrics
Play Observability Incident Triage
Algorithms Intermediate

Pattern Signal Arena

Recognize monotonic-stack, interval-merge, heap, and probabilistic membership signals from problem constraints.

Time
7-10 minutes
Concept
Algorithm pattern recognition
  • Algorithmic Reasoning
  • algorithms
  • heaps
  • intervals
Play Pattern Signal Arena
Databases Advanced

Query Plan Investigator

Investigate PostgreSQL query plans, cardinality gaps, scan choices, join amplification, and rollout evidence.

Time
9-12 minutes
Concept
SQL query planning and cardinality
  • Data & Performance
  • SQL Indexes
  • Performance
  • Databases
Play Query Plan Investigator
Scaling Intermediate

Rate Limit Architect

Choose rate limiting designs for realistic backend traffic patterns, from public APIs and login endpoints to queues, webhooks, and retry storms.

Time
6-9 minutes
Concept
Rate limiting, fairness, backpressure, and abuse protection
  • Data & Performance
  • Rate limiting
  • Scaling
  • 429
Play Rate Limit Architect
Databases Advanced

Replica Consistency Router

Route reads across primary and replicas while respecting lag, freshness contracts, failover, and workload isolation.

Time
8-12 minutes
Concept
Read replicas and consistency-aware routing
  • Database Reliability
  • replication
  • consistency
  • routing
Play Replica Consistency Router
Databases Intermediate

Recovery Objective Drill

Translate RPO and RTO into backup, point-in-time recovery, restore testing, and isolation decisions.

Time
7-10 minutes
Concept
Database backup and restore objectives
  • Database Reliability
  • backups
  • rpo
  • rto
Play Recovery Objective Drill
Databases Intermediate

Schema Migration Runbook

Choose safe zero-downtime database migration steps for expanding schemas, backfilling data, rolling out indexes, enforcing constraints, and recovering from failures.

Time
6-9 minutes
Concept
Zero-downtime schema migration planning and expand-contract releases
  • Data & Performance
  • Database Reliability
  • migrations
  • schema design
  • backfill
Play Schema Migration Runbook
Reliability Advanced

Slow Query & Change War Room

Triage blocking chains, slow-query regressions, expand-contract changes, and resource-safe database rollouts.

Time
10-12 minutes
Concept
Production database incident response
  • Data & Performance
  • Databases
  • Incidents
  • Schema Migrations
Play Slow Query & Change War Room
Observability Advanced

SLO Incident Commander

Direct incident response with RED, USE, service-level indicators, burn rates, and explicit recovery criteria.

Time
9-12 minutes
Concept
Service objectives and incident command
  • Production Reliability
  • Observability
  • SLO
  • Incidents
Play SLO Incident Commander
Spring Advanced

Spring Data Boundary Clinic

Place Spring transactions, JPA fetch plans, rollback rules, and validated configuration at production boundaries.

Time
9-11 minutes
Concept
Spring transaction and data boundaries
  • Spring Production
  • Transactions
  • SQL Indexes
  • Spring
Play Spring Data Boundary Clinic
Databases Intermediate

SQL Index Quest

Choose the best database index for simplified schemas and queries while learning full scans, covering indexes, sort avoidance, and composite order.

Time
7-10 minutes
Concept
Database indexing and query performance
  • Data & Performance
  • Algorithmic Reasoning
  • SQL
  • indexes
  • performance
Play SQL Index Quest
Observability Advanced

Telemetry Pipeline Builder

Build a bounded telemetry path for structured logs, trace context, sampling, batching, and safe attributes.

Time
9-11 minutes
Concept
Telemetry pipelines and context propagation
  • Production Reliability
  • Observability
  • Logs
  • Traces
Play Telemetry Pipeline Builder
Databases Advanced

Transaction Isolation Arena

Defend database invariants from concurrent requests by choosing transactions, locks, constraints, snapshot reads, and optimistic concurrency.

Time
7-10 minutes
Concept
Database transactions, isolation anomalies, locks, and invariant protection
  • Data & Performance
  • Database Reliability
  • SQL
  • transactions
  • isolation
Play Transaction Isolation Arena
APIs Intermediate

Webhook Signature Forensics

Investigate webhook requests and choose safe handling for signatures, replay windows, retries, idempotency, and durable acknowledgement.

Time
6-9 minutes
Concept
Webhook verification, replay protection, idempotency, and retry-safe processing
  • Foundations
  • webhooks
  • HMAC
  • idempotency
Play Webhook Signature Forensics