Why Cloud Bills Surprise People: The Usual Suspects

People budget for the servers they launch on purpose. Those are rarely the reason a bill is larger than expected. The surprises come from a short and fairly predictable list.

Stopped instances still cost money

Stopping a virtual machine usually stops the compute charge and nothing else. The disk attached to it continues to exist and continues to bill. A fleet of stopped machines kept just in case is a standing monthly charge.

Detached volumes and old snapshots

Delete a machine and its volume may survive, depending on how it was created. Detached volumes are attached to nothing, used by nobody and billed in full.

Snapshots behave similarly and multiply quietly, particularly where an automated policy creates one nightly and nothing ever removes them.

Reserved addresses that are not attached

Several providers charge for a reserved public address while it is not in use, precisely to discourage hoarding. Each is a small amount, and each runs indefinitely.

Data leaving the network

Inbound data is usually free. Outbound data to the internet is usually the most expensive transfer direction, and traffic between regions is billed too. A service that serves large files, or a backup job copying to another region nightly, can exceed the cost of the machine doing the work.

This is covered in more detail in bandwidth, egress and the cost of moving data.

Resources in regions nobody checks

Someone tested something in a distant region once. The console defaults to your usual region, so nothing appears wrong. The bill counts everything.

This is why a region sweep is part of any account audit.

Managed services with per-request pricing

Anything billed per request or per operation scales with traffic in a way that fixed-size machines do not. A retry loop or a misconfigured health check can multiply request counts without any visible change in application behaviour.

Credit running out

The most common surprise of all is not a new charge but the end of an offset. Nothing changed except that the promotional balance stopped absorbing it. See planning for credit expiry.

The habit that prevents most of this

Read the itemised bill once a month, sorted by cost, and ask what the top five lines are for. It takes five minutes and catches nearly everything on this list before it compounds.