SD-3N · Three Nines · 99.9%
Runbookly Certified System Design Engineer
Proves you can keep systems running at the Three Nines level of the System design lab: you solved the level in the simulator, then built and repaired real systems in a timed practical exam, without being able to test them.
- Practice
- 3 tasks · 70 %
- Theory
- 20 questions · 30 %
- Duration
- 2 h + 2 pauses of 10 min
- To pass
- 70 % overall, 60 % in practice
- Results
- 24 hours later
- Valid
- 24 months
The exam: practice first, then theory
70 %
Practice in the simulator
3 tasks in the lab you trained in: systems to build from a brief, or to repair. Some come from the level's exercises with other data, most were written for the exam only and are never published.
During the exam you cannot run the simulation: you build or repair, then submit. After the exam our servers replay each system through its day of traffic and failures, and grade it against its objectives.
30 %
Theory
Questions on production situations and on the concepts of the level, drawn for you among the level's exercises and the certification's own bank.
You pass with 70 % overall and at least 60 % in practice: a certified engineer must make systems hold, not only know the answers.
What to master
Every concept below can be asked, and every exercise of the level becomes a scenario of the exam.
- Quorums
- CAP theorem
- PACELC
- Tunable consistency
- Eventual consistency
- Sharding
- Partitioning strategies
- Consistent hashing
- Hot keys and hot partitions
- Write-ahead log
- Circuit breaker
- Cascading failures
- Timeouts
- Retries, backoff and jitter
- Graceful degradation
- Rate limiting
- Defense in depth
- Load shedding
- Consumer groups
- Event streaming
- Ordering guarantees
- Backpressure
- Caching
- Key-value stores
- Leader election
- Write concern and acknowledgement
- Replication
- Cache stampede
- Thundering herd
- Read replicas
- Capacity planning
- DDoS protection
- Anycast
- Cold starts
- Tail latency
- Little's law
- Serverless
- Cloud cost optimisation