MushyBook
All challenges

Right-size the runaway fleet

intermediate

Scenario & brief

A product API peaks at 8,000 requests/sec in the evening and must answer in under 120 ms at p99 with 99.95% availability and critical durability. The previous team left you:

  • 8× m5.4xlarge on-demand in a single AZ (fixed, all day)
  • no CloudFront in front, so every static asset hits the fleet
  • no cache, so the database eats the full read load
  • a single RDS instance — no Multi-AZ, no backups

The bill is ~$4,900/mo and it still misses the latency, availability, and durability targets.

Your goal: meet every SLA and bring the bill under $1,500/mo. Three stars if you get within ~10% of the leanest viable design.

8,000 rps peakp99 ≤ 120ms99.95% availdurability: criticalbudget $1,500/mo

CloudFront

Networking

System health

Erupting · SLA breach

24

/ 100

Score

SLA not met yet

Monthly cost

$4,876

Budget $1,500/mo · $3,376 over

Metrics

Capacity43
Availability30
Durability25
Cost efficiency0

Requirements

  • Peak capacity — 52000 rps compute · 3400 rps db (need ≥ 8000 rps)
  • p99 latency — ~134 ms (need ≤ 120 ms)
  • Availability — 99.00% (need ≥ 99.95%)
  • Durability — at risk (need redundancy + backups)
  • Budget — $4876/mo (need ≤ $1500/mo)

Advisor

  • The database is saturated at peak — add a cache to shed read load, or scale it up.
  • Compute runs in a single AZ — spread across ≥2 AZs (with ≥2 instances) to meet the availability target.
  • The database has no Multi-AZ standby or replica — a failure risks data loss. Enable Multi-AZ and backups.

Discussion

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For learning purposes only. Costs and capacities are illustrative, not live AWS prices. Not affiliated with or endorsed by Amazon Web Services.