Placement Groups

Placement Groups

Placement Groups

Hello Everyone

Welcome to CloudAffaire and this is Debjeet

In the last blog post, we have discussed how to create an Elastic IP address and assign to an instance.

In this blog post, we are going to discuss Placement Groups.

Placement Groups

Placement group determines how an instance will be placed on the underlying hardware. Generally, when we create an instance, we can define the instance geographic location using region and availability zones. But we want to control the instance placement on hardware, we need to use the placement group.

AWS provides two placement group strategies to implement

  • Cluster: clusters instances into a low-latency group in a single Availability Zone
  • Spread: spreads instances across underlying hardware

Cluster Placement Groups

A cluster placement group is a logical grouping of instances within a single Availability Zone. Cluster placement groups are recommended for applications that benefit from low network latency, high network throughput, or both, and if the majority of the network traffic is between the instances in the group. To provide the lowest latency and the highest packet-per-second network performance for your placement group, choose an instance type that supports enhanced networking.

A placement group can span peered VPCs in the same region. All nodes within the placement group can talk to all other nodes within the placement group at the full line rate of 10 Gbps flows and 25 aggregates without any slowing due to over-subscription.

Spread Placement Groups

A spread placement group is a group of instances that are each placed on distinct underlying hardware. Spread placement groups are recommended for applications that have a small number of critical instances that should be kept separate from each other. Launching instances in a spread placement group reduce the risk of simultaneous failures that might occur when instances share the same underlying hardware.

Spread placement groups provide access to distinct hardware and are therefore suitable for mixing instance types or launching instances over time. A spread placement group can span multiple Availability Zones, and you can have a maximum of seven running instances per Availability Zone per group.

Placement Group Rules and Limitations

  • The name you specify for a placement group must be unique within your AWS account for the region.
  • You can’t merge placement groups.
  • An instance can be launched in one placement group at a time; it cannot span multiple placement groups.
  • In the case of Reserved Instances, it is not possible to explicitly reserve capacity for a placement group.
  • Instances with a tenancy of host cannot be launched in placement groups.

The following rules apply to cluster placement groups only:

  • Not all instance types supported for cluster placement groups.
  • A cluster placement group can’t span multiple Availability Zones.
  • You can launch multiple instance types into a cluster placement group. However, AWS recommends using the same instance type for all instances in a cluster placement group.

The following rules apply to spread placement groups only:

  • A spread placement group supports a maximum of seven running instances per Availability Zone.
  • Spread placement groups are not supported for Dedicated Instances or Dedicated Hosts.

Hope you have enjoyed this blog post. In the next blog, we are going to create instances using placement groups.


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