Understanding and controlling cloud costs
Summary: the cloud bill is the first source of bad surprises for organizations that migrate. This lesson explains how the cloud is really billed, details the seven most expensive traps, presents the optimization levers ranked by yield, and introduces the FinOps approach.
1. How the cloud is billed
The transfer asymmetry is deliberate: bringing your data in is free, getting it out is billed. It is not a coincidence — it is an economic mechanism that makes leaving expensive. Since 2024, under pressure from the European data regulation, the big providers offer free outbound transfers in case of complete termination, but everyday egress remains billed.
2. The seven traps that make a bill explode
Trap 1 is by far the most expensive in reality. Industry studies regularly estimate that a very significant share of cloud spending corresponds to unused or overprovisioned resources. It is not negligence — it is the natural consequence of a system where creating is easy and free in the moment, while deleting requires knowing the resource exists.
3. The optimization levers, by yield
Start imperatively with levers 1 and 2. They require little effort, need no financial commitment, and produce visible results in a few days. Many organizations rush to reserved instances (lever 4) — thereby committing for three years to pay for overprovisioned resources.
The correct order is: clean up, then right-size, then only commit on duration.
4. Understanding reserved and spot instances
Concrete advice on interruptible instances: they are perfect for your CI/CD pipelines. A build job that gets interrupted can simply be relaunched, and you pay 70 to 90% less. It is one of the most profitable and least risky optimizations there is.
5. The total cost of ownership calculation
Comparing a cloud bill to a server's price is a frequent methodological error.
The systematic bias to know: the cloud bill is a visible line in a budget, while the costs of an owned server are scattered between investment, real estate, energy, licences and salaries. This creates an illusion that the cloud costs more — while a complete cost is compared to a partial cost.
In the opposite direction, for honesty: for a perfectly stable load over five years, even counting everything, owned hardware can really cost two to three times less. Both statements are true depending on the load profile.
6. The FinOps approach
The most important FinOps principle: the person able to say "this database can go from 16 to 4 processors" is the engineer who created it, not the management controller. Finance's role is to make the cost visible to the team that generates it. It is this visibility that produces the optimization, not top-down directives.
7. The practices to put in place from day one
Practice 1 is absolutely non-negotiable. A configuration mistake — a loop creating resources, an image-processing service without limits, a leaked key exploited for mining — can generate thousands of euros in one night. A budget alert is your only safety net. Five minutes of configuration.
8. The free tier — what it really allows
Recommendation for learning without risk: create an account, immediately configure a budget alert at 5 euros, and do your experiments. Also get into the habit of deleting what you create at the end of each learning session.
Remember in 30 seconds
- The cloud bills compute, storage, transfers, requests and managed services.
- Egress (outbound data) is billed, ingress is free. It is the most underestimated item.
- Trap number one: forgotten resources — test machines, orphan disks, never-purged backups.
- Correct optimization order: clean up → turn off non-production → right-size → then commit on duration.
- Turning off non-production at night and at the weekend saves about 65% on these environments.
- Interruptible (spot) instances: 60 to 90% discount, perfect for CI/CD and batch processing.
- Comparing cloud and owned server requires counting human time and unused capacity, systematically omitted.
- FinOps: it is the engineers who optimize, finance makes the cost visible.
- Configure a budget alert as soon as the account is created. Five minutes, and it avoids dramas.