Real MongoDB sandbox
Every scenario runs an actual MongoDB instance in a container — not a multiple-choice quiz or a video.
Labs · MongoDB
Practice real MongoDB scenarios before they happen
Practice the MongoDB failures that hit in production — collection scans, aggregation blowups, election storms, oplog lag and sharding hot spots — against a real MongoDB sandbox.
Run rillence mongodb · real MongoDB in Docker · deterministic scoring.
What it is
A flight simulator for MongoDB operations
Boot a real MongoDB in a container, inject a realistic failure, and investigate with mongosh or your own tooling. Deterministic scoring, zero production risk.
Real scenarios
Collection scans, aggregation blowups, election storms, oplog lag and sharding hot spots — injected into a live instance.
AI hints + deterministic scoring
Get progressive hints while you investigate, a scorecard for your fix and a postmortem explaining the root cause.
Built for individuals and teams
Practice alone, onboard new engineers, or run repeatable internal MongoDB team drills.
Scenarios
MongoDB scenarios, grouped into tracks
The MongoDB failure modes engineers actually meet in production — from explain() to replica sets and sharding.
Query Performance & Indexes
CoreMissing compound indexes, wrong field order, uncovered sorts, regex scans and multikey surprises.
Aggregation Pipeline Performance
Core$lookup explosions, $unwind blowups, $group memory pressure and unindexed $sort.
Drivers, Connections & App Integration
CoreConnection-pool exhaustion, connection leaks, retryable writes and read preferences.
Operations, Transactions & Long-Running Work
OperationsLong transactions, lock contention, slow bulk jobs and index builds under load.
Replica Sets & Elections
OperationsElection storms, stepdowns that drop writes, lagging secondaries and write-concern stalls.
Oplog, Consistency & Read/Write Concerns
OperationsOplog window loss, rollback, stale reads and mis-set read/write concerns.
Sharding, Balancer & Routing
AdvancedHot shards, jumbo chunks, balancer storms and bad shard-key routing.
Storage, WiredTiger & Disk Pressure
OperationsCache pressure, checkpoint stalls, disk-full and compaction surprises.
Backup, Restore & Disaster Recovery
OperationsBad backups, slow restores, PITR gaps and recovery drills.
Multi-Database, Tenancy, Schema & Access
AdvancedSchema drift, tenant isolation, access scoping and multi-database operations.
Compound Production Incidents
CapstoneMulti-cause GameDays mixing queries, replication and sharding under pressure.
Incident Control
CapstoneIncident-commander scenarios coordinating diagnosis and fix under pressure.
How practice works
From paged to postmortem in four steps
Launch the lab
Run rillence mongodb to open the interactive REPL.
Start a scenario
Pick a scenario from any track and boot an isolated MongoDB sandbox.
Investigate
Connect with mongosh — or any client you already use — and dig in.
Submit and score
Get deterministic Detect / Fix / Trap scoring and a postmortem.
Practice MongoDB scenarios before they become outages
One subscription covers every lab. Train your judgment in a safe sandbox, not in production.