Cloud cost
On-demand vs. spot instances
On-demand pricing charges the full published rate with no commitment; spot pricing sells unused capacity at a steep discount but can be reclaimed with little notice.
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Definition
On-demand is the default, most-expensive-per-hour way to pay for compute: no commitment, no discount, billed only for what you use. Spot capacity is the provider's unused inventory, sold at a discount that can reach 70–90% off on-demand. The tradeoff is that the provider can reclaim a spot instance with as little as a couple minutes' warning when it needs the capacity back.
Spot fits stateless, interruption-tolerant workloads (batch jobs, CI runners, fault-tolerant worker fleets) extremely well and is a poor fit for anything that can't gracefully checkpoint or restart.
Where it shows up
On the bill, on-demand and spot usage of the same instance type appear as separate line items at their own published rates. In the console, a spot request carries its own status field, and AWS sends an interruption notice a short time before it reclaims that capacity.
What makes it expensive
Can this workload survive losing its instance mid-run? Answer that before moving anything stateful onto spot capacity, because an interruption there is routine rather than rare. A fleet that starts absorbing more interruptions has not become less suited to spot. It was never suited, and the discount was covering the cost of every restart.
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- Savings plan (SP)
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- 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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