HTTP Status Defender
Choose precise HTTP responses for realistic API outcomes.
Open practicePractice lab
Turn backend concepts into decisions.
Short, focused scenarios help you apply course ideas. Games open on Backend Study Lab · Games and keep separate local progress.
API Route Builder
Build clear resource routes and choose safe methods.
Open practiceAuth Token Inspector
Inspect authentication boundaries, token decisions, and OpenAPI security schemes.
Open practiceCORS Preflight Pilot
Reason through exact origins, preflights, credentials, and response headers.
Open practiceWebhook Signature Forensics
Validate signed requests, timestamps, replay protection, and trust boundaries.
Open practiceSQL Index Quest
Match query shapes to useful index strategies.
Open practiceTransaction Isolation Arena
Protect correctness across isolation anomalies and concurrent database work.
Open practiceSchema Migration Runbook
Sequence safe schema changes and rollback decisions.
Open practiceCache Eviction Lab
Choose application-cache eviction policies under changing workloads.
Open practiceRate Limit Architect
Select limits that protect systems without surprising clients.
Open practiceLoad Balancer Challenge
Route traffic while preserving availability and affinity.
Open practiceMessage Queue Simulator
Control worker capacity, retries, ordering, and poison-message handling.
Open practiceIdempotency Key Clinic
Prevent duplicate API effects across retries and failures.
Open practiceObservability Incident Triage
Use signals and context to isolate production incidents.
Open practiceCircuit Breaker Clinic
Tune resilience behavior around failing dependencies.
Open practiceOutbox Relay Recovery
Recover atomic publication intent through relay crashes and duplicate sends.
Open practiceDelivery Guarantee Timeline
Trace acknowledgments, crashes, retries, and real processing guarantees.
Open practiceIdempotent Consumer Lab
Build duplicate-safe consumers with database invariants.
Open practiceDLQ Recovery Console
Classify, quarantine, remediate, approve, and replay failed messages.
Open practiceSaga Compensation Orchestrator
Coordinate durable state, compensations, timeouts, and manual recovery.
Open practicePartition Tradeoff Commander
Choose explicit consistency and availability behavior during partitions.
Open practiceReplica Consistency Router
Route reads around lag, freshness contracts, failover, and workload isolation.
Open practiceRecovery Objective Drill
Translate RPO and RTO into tested backup and restore controls.
Open practiceDeadlock Detective
Read waits-for cycles and choose safe prevention and retry actions.
Open practiceHTTP Cache Policy Lab
Design explicit public, private, validated, and variant response policies.
Open practiceETag & CDN Revalidation Lab
Operate validators, 304 responses, CDN invalidation, and bounded staleness.
Open practiceOAuth Code Flow Debugger
Repair state, PKCE, redirect, exchange, and session boundaries.
Open practicePassword Reset Defense Lab
Secure recovery against enumeration, token theft, replay, and stale sessions.
Open practicePattern Signal Arena
Recognize monotonic-stack, interval, heap, and membership signals.
Open practiceGraph Traversal Navigator
Choose BFS or DFS and handle cycles and disconnected components.
Open practiceBloom Filter Tuner
Tune capacity, hash count, false positives, and deletion behavior.
Open practiceQuery Plan Investigator
Read query-plan evidence before changing indexes, SQL, or capacity.
Open practiceIndex & Storage Strategy Lab
Choose index and storage boundaries for predicates, churn, and retention.
Open practiceSlow Query & Change War Room
Triage query regressions, blocking chains, and zero-downtime changes.
Open practiceTelemetry Pipeline Builder
Build bounded logging, trace-context, sampling, and export pipelines.
Open practiceSLO Incident Commander
Direct incidents with service objectives, burn rates, and recovery evidence.
Open practiceDeadline & Isolation Simulator
Propagate deadlines and isolate resources before dependency failure spreads.
Open practiceOverload Control Room
Control queues, concurrency, probes, and priority-aware load shedding.
Open practiceSpring Request Boundary Lab
Design validation, controller, service, and stable error boundaries.
Open practiceSpring Data Boundary Clinic
Place transactions, JPA fetch plans, rollback, and configuration checks.
Open practiceSpring Production Readiness Drill
Sequence security, health, integration testing, and incident recovery.
Open practiceEvent Contract Evolution Lab
Evolve event envelopes and schemas without breaking producer or consumer meaning.
Open practiceKafka Partition & Ordering Control Room
Control keys, rebalances, ordering gaps, and hot-partition recovery.
Open practiceEvent Recovery Incident Drill
Recover publication, backlog, and business state across event-driven incidents.
Open practiceJava Memory & Synchronization Lab
Protect visibility, compound invariants, atomics, and lock ordering.
Open practiceExecutor & Cancellation Control Room
Bound task admission, compose failures, and propagate cancellation.
Open practiceVirtual Thread Incident Drill
Operate virtual threads, structured tasks, scoped context, and pinning evidence.
Open practiceContainer Artifact Trust Chain
Build, attest, and promote one minimal immutable container artifact.
Open practiceKubernetes Workload Boundary Lab
Connect workload controllers, identity, probes, and graceful termination.
Open practiceKubernetes Capacity & Rollout Commander
Preserve serving capacity through scheduling, autoscaling, and rollouts.
Open practiceKubernetes Incident Recovery Drill
Recover workload failures from controller, runtime, and business evidence.
Open practiceDatabase Engine & Capacity Lab
Connect durability, MVCC, plan evidence, and connection budgets.
Open practiceDatabase Failover & Contention War Room
Recover pool, lock, replication, and failover incidents safely.
Open practiceTelemetry Contract & Instrumentation Lab
Build trustworthy telemetry ownership, cardinality, propagation, and compatibility boundaries.
Open practiceSRE Alert & Incident Command Drill
Route actionable alerts, assign incident roles, and verify durable recovery.
Open practiceJVM Runtime Evidence Triage
Correlate CPU, thread dumps, safepoints, JFR, dependencies, and container evidence.
Open practiceJVM Heap & Native Memory Forensics
Separate retained heap, allocation churn, native memory, RSS, and container pressure.
Open practiceJVM GC Collector Control Room
Diagnose G1 and ZGC with unified evidence and reversible experiments.
Open practiceJVM Warmup & Capacity Lab
Measure JIT, code cache, warmup, AOT, and capacity with explicit rollback.
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