A team wants guaranteed On-Demand capacity for an m5.large in a specific Availability Zone for an upcoming three-day event, starting immediately, with no long-term commitment, and they also want those instances to run inside a placement group. Which combination is valid?
- An On-Demand Capacity Reservation combined with a Spread placement group
- An On-Demand Capacity Reservation for immediate use combined with a Cluster placement group
- A one-year Standard Reserved Instance combined with a Dedicated Host
- An On-Demand Capacity Reservation combined with a Partition placement group
Why B? And why not the others?
Correct answer: B. An On-Demand Capacity Reservation for immediate use combined with a Cluster placement group
On-Demand Capacity Reservations created for immediate use carry no term commitment at all — they can be created, modified, or canceled at any time — which matches a short, three-day, no-commitment requirement, and Capacity Reservations are explicitly supported alongside Cluster placement groups, letting instances that need guaranteed capacity also gain a Cluster placement group's low-latency, high-throughput packing. Spread and Partition placement groups, however, are not supported with Capacity Reservations at all, so pairing a Capacity Reservation with either one is not a configuration AWS allows, ruling out those combinations regardless of how appealing the isolation or distribution properties might otherwise be. A one-year Standard Reserved Instance fails on two counts here: it locks in a full one-year term that doesn't fit a three-day event, and separately, Capacity Reservations, not Reserved Instances, are the construct that can't be combined with Dedicated Hosts — Dedicated Hosts have their own distinct host-allocation mechanism that doesn't combine with either reservation type in this way.
Source: AWS EC2 documentation: EC2 Capacity Reservations — placement group and Dedicated Host limitations