Lesson 6 of 6
Lesson 6 — Cost, Scaling Strategy and Green Cloud
FinOps for teenagers: why an idle test environment can cost more than a games console every month.
Learn it
Cloud bills grow from things you forgot to turn off, and from moving data out of the provider (egress).
Auto-scaling saves money only if it also scales down.
Data centres use a lot of electricity and water — where and when you run code affects its carbon footprint.
Key terms
- Egress
- Data leaving the cloud provider's network — usually billed per GB.
- Spot instance
- Deeply discounted spare capacity that can be reclaimed at short notice.
- Right-sizing
- Matching instance size to measured demand instead of guesswork.
- FinOps
- Treating cloud cost as an engineering metric owned by the whole team.
- PUE
- Power Usage Effectiveness — total data-centre energy divided by IT energy.
Audit a surprise €600 bill
A student project's monthly invoice arrives and nobody knows why.
- 1Clue 1: Three GPU instances launched for one afternoon's experiment are still running — 41 days later.
- 2Clue 2: Debug logging writes 20 GB/day and retention is set to 'never delete'.
- 3Clue 3: A public dataset is re-downloaded from the bucket by an external script — that's egress, billed per GB.
- 4Fix: Terminate idle instances, set log retention to 14 days, cache the dataset behind a CDN, add a €50 budget alert.
Cost of forgetting
pythonHOURS_PER_MONTH = 730
def monthly(rate_per_hour, count=1, hours=HOURS_PER_MONTH):
return round(rate_per_hour * count * hours, 2)
print(monthly(1.20, 3)) # 3 idle GPU boxes -> 2628.00
print(monthly(0.0104, 1)) # 1 tiny always-on VM -> 7.59
print(monthly(1.20, 3, 4)) # same GPUs, shut down after 4h -> 14.40Same hardware, two orders of magnitude difference. The bill is decided by how long things stay on, not by how powerful they are.
Sandbox lab
Practise the real technique in a fully simulated environment — no live systems, no real data, nothing leaves your browser.
Cloud cost simulator
Architect the stack, then get graded on cost, performance, reliability and waste.
A mostly-static school website. Traffic is small and steady, images are read constantly, budget is tight.
Storage class
Compute
Scaling strategy
Database
Try it
Order these workloads from best-suited to worst-suited for spot instances.
- 1CI test runners
- 2Live payment checkout service
- 3Internal reporting dashboard
- 4Overnight video re-encoding batch
Challenge
Your class's cloud budget is €40/month but the current setup costs €190. Propose a cost-reduction plan that keeps the live demo site fast, and estimate the impact of each change.
Pick whichever way suits you — every mode earns the same bonus XP.
Write at least 40 more characters to submit.
Mark your own work
Guided walkthrough — 0/3 clues revealed
- Clue 1 locked — reveal it only if you get stuck.
- Clue 2 locked — reveal it only if you get stuck.
- Clue 3 locked — reveal it only if you get stuck.
Each clue costs 5 XP (never below 24 XP). You'd earn 48 XP right now.