Cloud cost
Savings plan
A commitment to a dollar-per-hour spend level. It applies automatically across compute, whatever the instance family.
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Definition
A reserved instance locks in an instance shape. A savings plan locks in a spend rate. Say you commit to $10 an hour of compute for one or three years. The discount then applies to whatever instance types and sizes you run, up to that amount. The discount is usually a little smaller than for an equal reserved instance.
Savings plans suit teams whose instance mix changes over time. Reserved instances suit a stable, predictable footprint.
Where it shows up
A savings plan appears on the bill as its own Savings Plans charge type. AWS applies it to whatever instance family and size ran that hour, up to the committed spend rate. Usage above the commitment falls back to the on-demand rate on the same line.
What makes it expensive
A plan can stop matching a shrinking footprint. You then pay for a commitment that real usage no longer covers. The utilization report shows the gap between what you committed and what the plan covered. Read it as often as you read reserved instance coverage. The two failures look very different.
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- Reserved instance (RI)
- On-demand vs. spot instances
- Data egress
- Amortized, blended, and unblended cost
- Billed vs. effective vs. list vs. contracted cost
- Rightsizing
- Idle and orphaned resources
- Storage class
- Lifecycle policy
- Incremental snapshot
- Allocatable capacity
- Requests vs. limits
- Cluster idle
- Workload idle
- Bin packing
- Cost allocation tags
- Tag coverage
- Unallocated spend
- Showback vs. chargeback
- Unit economics
- RI/SP coverage and utilization
- Observability tax
- Metric cardinality
- High-water-mark billing
- Log ingest vs. index
- Snowflake credit
- Auto-suspend / resume minimum
- BigQuery slot
- Bytes scanned & partition pruning
- Time Travel & Fail-safe
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