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Placement Groups In AWS

In this article, we will discuss the placement groups in AWS.

Purpose

Placement groups are used to control the placement of EC2 instances for a region and availability zone. While creating the placement groups, you create a strategy based on which, the EC2 instances are placed.

Different Strategies Of The Placement Group

There are three strategies for the placement groups: -

Cluster → In this strategy, the EC2 instances are placed close to each other in the same availability zone
Partition → In this strategy, the EC2 instances are grouped in a segment called Partition. Each partition does not share the same underlying hardware
Spread → In this strategy, the small group of EC2 instances is placed on distinct hardware

The key difference between the Partition and Spread strategies is that there are a maximum of seven running instances per availability zone.

	Clustered	Spread	Partition
What	Instances are placed into a low-latency group within a single AZ	Instances are spread across underlying hardware	Instances are grouped into logical segments called partitions which use distinct hardware
When	Need low network latency and/or high network throughput	Reduce the risk of simultaneous instance failure if underlying hardware fails	Need control and visibility into instance placement
Pros	Get the most out of enhanced networking Instances	Can span multiple AZs	Reduces the likelihood of correlated failures for large workloads.
Cons	Finite capacity: recommend launching all you might need upfront	Maximum of 7 instances running per group, per AZ	Partition placement groups are not supported by Dedicated Hosts

How To Create The Placement Group?

To create the placement group, click on the Placement Groups menu in the EC2 dashboard.

Picture showing the Placement Groups menu in EC2 dashboard

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A screen will appear on the right-hand side. Click on the Create placement group button.

Picture showing the Create placement group button for creating the new placement group

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The Create placement group screen will appear. Enter the following information: -

Field	Value
Name	< Custom placement group name>
Placement strategy	Cluster \| Spread \| Partition
Number of partitions	< Number of partitions >
Spread level	Host (Outposts only) \| Rack (No restrictions)This field is visible only if “Spread” is selected in “Placement strategy”.

Picture showing the create placement group screen with placement strategy as cluster

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Picture showing the create placement group screen with placement strategy as spread

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Picture showing the create placement group screen with placement strategy as partition

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Click on the Create group button. The placement group is created.

Picture showing the placement group created in aws console

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How To Assign A Placement Group To An EC2 Instance?

To assign the placement group in an EC2 instance, select the Placement group name while launching the EC2 instance.

Picture showing assigning the placement group to an EC2 instance

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Posted By -	Karan Gupta

Posted On -	Friday, July 22, 2022

Updated On -	Monday, January 16, 2023

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