EC2 Purchase Options
Every EC2 instance runs under one of a handful of purchase options. They trade three things against each other: price, commitment, and whether capacity is guaranteed. Getting them mixed up is expensive in one direction and risky in the other — most notably, a discount is not the same as a capacity guarantee.
On-Demand
Section titled “On-Demand”- Billed per second (60-second minimum for Linux) with no commitment
- The most flexible and the most expensive per hour
- Right for short-lived, spiky or genuinely unpredictable work, and for the first weeks of anything new while you learn its shape
Reserved Instances
Section titled “Reserved Instances”A one- or three-year commitment to a particular instance configuration, in exchange for a discount of up to around 72% against On-Demand. Payment can be all upfront (largest discount), partial upfront, or no upfront.
Scope matters, and it is the thing people get wrong. A Reserved Instance is either regional or zonal:
| Regional RI | Zonal RI | |
|---|---|---|
| Reserves capacity | No | Yes, in the specified Availability Zone |
| Availability Zone flexibility | Discount applies in any AZ in the Region | None — the specified AZ only |
| Instance size flexibility | Discount applies across sizes in the family (Linux/Unix, default tenancy) | None — the exact size only |
| Queue a future purchase | Yes | No |
The scope does not change the price. If you need a capacity guarantee for a launch-critical workload, a regional RI does not give you one — use a zonal RI or an On-Demand Capacity Reservation.
Standard RIs cannot be changed after purchase. Convertible RIs can be exchanged for a different instance family, operating system, tenancy or payment option, at a smaller discount.
Savings Plans
Section titled “Savings Plans”A commitment to a level of hourly spend rather than to a specific instance, for one or three years.
- Compute Savings Plans apply automatically across EC2, Fargate and Lambda, across instance families, sizes, operating systems, tenancies and Regions.
- EC2 Instance Savings Plans commit to a family in a Region, for a larger discount and less flexibility.
For most estates a Compute Savings Plan is the better instrument than Reserved Instances: it covers container and serverless spend as well as EC2, and it survives a change of instance family. Like a regional RI, it reserves no capacity — it is purely a billing discount.
Spot Instances
Section titled “Spot Instances”Spare EC2 capacity at a discount of up to about 90%. AWS can reclaim the instance at any time with a two-minute interruption notice. There is no bidding: you request capacity, optionally set a maximum price, and pay the current Spot price, which moves gradually with supply and demand.
Spot suits work that is stateless, checkpointed, or easy to restart: CI runners, batch and rendering, data processing, and stateless web tiers behind a load balancer alongside On-Demand capacity. Diversify across several instance types and Availability Zones and use the price-capacity-optimized allocation strategy, which favours pools that are both cheap and deep. See Spot Instances, EC2 Fleet and Auto Scaling groups.
Dedicated Instances and Dedicated Hosts
Section titled “Dedicated Instances and Dedicated Hosts”- Dedicated Instances run on hardware not shared with other AWS accounts.
- Dedicated Hosts give you a whole physical server, with visibility of its sockets and cores.
Dedicated Hosts are the more expensive of the two and exist mainly for licensing: per-socket, per-core or per-VM software licences that must be tied to identifiable hardware, and bring-your-own-licence arrangements. Both can be combined with Reserved Instances or Savings Plans.
On-Demand Capacity Reservations
Section titled “On-Demand Capacity Reservations”Reserve capacity of a specific instance type in a specific Availability Zone, for as long as you want, and cancel when you are done.
- Pays On-Demand rates for the reserved capacity whether or not you use it
- No discount on its own, but it can be combined with a Savings Plan or a regional RI so you get both the guarantee and the discount
- The right tool for a launch, a failover region, a disaster-recovery drill, or any moment when “no capacity available” is not an acceptable answer
Choosing
Section titled “Choosing”| Situation | Option |
|---|---|
| New or unpredictable workload | On-Demand |
| Steady baseline across a mixed estate | Compute Savings Plan |
| Steady baseline pinned to one family and Region | EC2 Instance Savings Plan or Reserved Instances |
| Interruptible, restartable, or horizontally scaled work | Spot |
| Capacity must be there at a known moment | On-Demand Capacity Reservation, or a zonal RI |
| Licensing tied to physical hardware | Dedicated Hosts |
Most production estates end up with a mixture: a Savings Plan covering the baseline, On-Demand absorbing the daily peak, and Spot doing the interruptible work.