Placement groups for your Amazon EC2 instances - Amazon Elastic Compute Cloud

Placement groups for your Amazon EC2 instances

To meet the needs of your workload, you can launch a group of interdependent EC2 instances into a placement group to influence their placement.

Depending on the type of workload, you can create a placement group using one of the following placement strategies:

  • Cluster – Packs instances close together inside an Availability Zone. This strategy enables workloads to achieve the low-latency network performance necessary for tightly-coupled node-to-node communication that is typical of high-performance computing (HPC) applications.

  • Partition – Spreads your instances across logical partitions such that groups of instances in one partition do not share the underlying hardware with groups of instances in different partitions. This strategy is typically used by large distributed and replicated workloads, such as Hadoop, Cassandra, and Kafka.

  • Spread – Strictly places a small group of instances across distinct underlying hardware to reduce correlated failures.

Placement groups are optional. If you don't launch your instances into a placement group, EC2 tries to place the instances in such a way that all of your instances are spread out across the underlying hardware to minimize correlated failures.

Pricing

There is no charge for creating a placement group.

Rules and limitations

Before you use placement groups, be aware of the following rules:

  • An instance can be placed in one placement group at a time; you can't place an instance in multiple placement groups.

  • You can't merge placement groups.

  • On-Demand Capacity Reservations and zonal Reserved Instances allow you to reserve capacity for EC2 instances in Availability Zones. When you launch an instance, if the instance attributes match those specified by an On-Demand Capacity Reservation or a zonal Reserved Instance, then the reserved capacity is automatically used by the instance. This is also true if you launch the instance into a placement group.

  • You can't launch Dedicated Hosts in placement groups.

  • You can't launch a Spot Instance that is configured to stop or hibernate on interruption in a placement group.

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