AWS EC2 Placement Groups

Placement Groups allow users to influence the placement of EC2 Instances within AWS’s Infrastructure.

Types of Placement Groups

• Cluster Placement Group

• Spread Placement Group

• Partition Placement Group

Cluster Placement Group

Is the logical grouping of instances within an Availability Zone. Cluster Group can span across peered VPCs. Cluster Groups are ideal for scenarios requiring high network throughput or low network latency.

Considerations

• Cannot span across Availability Zones

• Adding instances to existing cluster group may result in insufficient capacity error. Requires re-deployment of the cluster group with the updated number of instances.

• An instances in a cluster group can be stopped but restarting the instance depends on the availability of the hardware. Issues with capacity requires redeployment of the cluster group.

• Multiple Instance types can be launched in a cluster group but the required capacity may not be available.

Spread Placement Group

Instances are deployed on distinct hardware. Each instance has unique set of hardware, and other equipment. Suitable for critical workloads that require high availability. Reduces the risk of simultaneous failures.

Considerations

• Launch request fail if distinct hardware and equipment are not available

• Dedicated Instance types are not supported for spread placement group

Partition Placement Group

EC2 instances are grouped into partitions. An EC2 instances in a partition does not share the same rack with an EC2 instance in other partitions. A hardware failure in one of the partition does not affect the instances of other partitions. Partition placement groups are best for application requiring high availability.

Considerations

• Each Partition Group allows a maximum of seven partitions per Availability Zone.

• The number of Instance in a partition group is only limited by the limit of the AWS account

• Best Effort Even instance distribution to partitions i.e, no guarantee of even distribution of EC2 instances across partitions

• A partition placement group comprising of a Dedicated Instance type of EC2 , can only have a maximum of two partitions