Outcome
By the end of this lesson, you will be able to explain why idle and stopped resources still cost money, and list what keeps billing after a machine is switched off.
| Prerequisites | L1 |
| Time | 8 minutes |
1. Concept
Here is the single most useful fact about cloud cost: for rented machines and disks, the provider charges for what you have reserved, not for what you used. Serverless functions and request meters are different: they charge per use.
A rented machine is set aside for you. Nobody else can use it while you hold it. So the provider charges for every hour you hold it, whether it is working flat out or doing nothing at all. A machine that is idle (switched on, but doing little or no useful work) costs exactly the same as a busy one.
Think of a hotel room. You pay for every night you book it, whether you sleep there or not. The hotel cannot rent it to someone else while it is yours.
Stopping a machine: what stops and what does not
Most providers let you stop a virtual machine (switch it off without deleting it) and start it again later. When you do:
- The compute charge stops. You no longer pay the hourly price for the machine itself.
- The disk keeps billing. The disk attached to the machine still holds your data, so you still pay for it per GB-month.
- Some extras keep billing. A fixed public internet address reserved for the machine, for example, is usually still charged.
One provider detail is worth knowing. On Azure, shutting a machine down from inside its own operating system leaves it in a “Stopped” state where the compute charge continues. You have to choose Stop in the Azure portal, which “deallocates” it (hands the hardware back), for the compute charge to stop.
Deleting: when the meter really stops
The meter only stops completely when the resource is deleted. Even then, look for what it leaves behind:
- Snapshots. A snapshot is a saved copy of a disk at one moment, kept in case you need to restore it. Snapshots are billed per GB-month and are not always deleted with the machine.
- Unattached disks. On some setups, deleting a machine does not delete its disks. They sit there, attached to nothing, still billing.
- Reserved addresses, load balancers and gateways. Network pieces created for the machine can outlive it.
Resources that keep billing after the thing they served is gone are often called orphaned resources.
Why this happens so often
Nobody gets an alert when something is idle. Nothing breaks. The bill simply arrives a little higher each month. Test machines left on over the weekend, a disk kept “just in case”, a copy of a system from a project that ended: each one is small, and together they add up.
2. Worked example
A developer creates a test machine on Monday, finishes with it on Wednesday and forgets about it. Illustrative prices:
| What | Unit price | Amount | Monthly cost |
|---|---|---|---|
| Machine, left running all month | $0.20 per hour | 730 hours | $146 |
| Its 200 GB disk | $0.08 per GB-month | 200 GB | $16 |
| Total if left running | $162 |
Three options:
| Action | What still bills | Monthly cost |
|---|---|---|
| Leave it running | Machine and disk | $162 |
| Stop it | Disk only | $16 |
| Delete machine and disk | Nothing | $0 |
Stopping saves most of the money, but not all of it. If the disk is not needed, deleting is the only way to reach zero. If the developer had also taken a 200 GB snapshot at an illustrative $0.05 per GB-month, that would add $10 a month until someone deleted it too.
3. Hands-on (5 min: no account needed)
1. Open the AWS EBS pricing page: aws.amazon.com/ebs/pricing2. Find the price per GB-month for a general purpose SSD volume (gp3) in any region.3. Find the price per GB-month for EBS snapshots in the same region.4. Work out what a forgotten 500 GB disk costs per month, and per year.5. Do the same for a forgotten 500 GB snapshot.Those are costs that keep running after a machine is stopped, or after it is deleted, until someone notices them.
4. Knowledge check
Q1
A machine is switched on all month but does almost no work. How is it charged?
A. At a reduced idle rate
B. Only for the minutes it was busy
C. At the full hourly price for every hour it was on
D. Not at all, because the provider can see it was idle
Show answer
Correct: C. You are charged for holding the machine, not for how hard it works. There is no idle discount.
Q2
You stop a virtual machine but do not delete it. What usually keeps costing money?
A. Nothing; stopping ends every charge
B. Its disk, and any fixed public address kept for it
C. The full hourly price of the machine
D. Only the operating system licence, at a reduced rate
Show answer
Correct: B. Stopping ends the compute charge, but the disk still holds your data and keeps billing per GB-month, and a reserved public address usually keeps billing too. On Azure, remember to stop (deallocate) from the portal, or the compute charge continues.
Q3
What is an orphaned resource?
A. A resource that bills on after the thing it served is gone
B. A resource that belongs to a team with no manager
C. A machine that has been running for more than a year
D. A resource bought with a long-term discount
Show answer
Correct: A. Unattached disks, old snapshots and leftover network pieces are typical orphans. They keep billing quietly because nothing alerts on them.
5. Apply
When someone says “we turned it off”, ask two follow-up questions. Was it stopped or deleted? And what did it leave behind: disks, snapshots, addresses? The answer to those two questions is the difference between saving most of the cost and saving all of it.
Related lessons
- L1, Per hour, per GB, per request: the units of price
- L3, Moving data: in is usually free, out is not (next)
- I.4 L4: Why sprawl happens