Cloud cost
Reserved instance
A commitment to one instance type in one region or zone, priced below on-demand.
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Definition
A reserved instance is the older and more rigid kind of committed use discount. You commit to one instance family and size. In return, you pay a lower hourly rate, or a fully upfront rate, for the term. The fixed shape earns a deeper discount than a savings plan. It does not flex when your instance mix changes.
Revisit your reservations when the architecture changes. A reservation for an instance type you left stops paying for itself. It becomes a stranded commitment.
Where it shows up
A reserved instance appears on the bill as its own charge line. The line ties to one instance family, one size, and one region or Availability Zone. AWS Cost Explorer's RI reports break it out from on-demand usage of the same instance type. They show the discounted rate next to the remaining term.
What makes it expensive
A reservation often outlives the design that justified it. Move off that instance family and the reservation keeps billing at the committed rate while it covers nothing. Utilization on that one reservation falls. The account total barely moves, so nothing draws attention to it. Review reservations one at a time, not as a total.
Related
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- RI/SP coverage and utilization
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- High-water-mark billing
- Log ingest vs. index
- Snowflake credit
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- BigQuery slot
- Bytes scanned & partition pruning
- Time Travel & Fail-safe
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