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How do Target groups and Placement Groups work together, or influence each other?

Is it possible to have an overlap between these two types of groupings?

For example if I have an ELB pointing to a Target Group in Av

Ntobeko Mkhize
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I don't think these concepts are related and they do not influence each other.

A target group is a group of instances that your ALB will distribute requests across.

A placement group is a group of instances that are colocated on physical hardware based on a specific configuration (they could be configured to be very close to improve latency or configured to be spread over hardware to reduce correlated errors).

A target group can consistent of instances that are part of zero, one or many placement groups.

JD D
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  • Just some additional note: Placement Groups are related to placement of Autoscaled Instances. Target Groups contain Load Balancer targets. – hargut Jun 20 '19 at 08:30
  • Thanks for the responses. So in a case where an instance is part of a placement group, and that instance also falls part of a target group. If the placement group were to be be stopped would that cause the target group to spin-up new instances? – Ntobeko Mkhize Jun 21 '19 at 08:43
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Placement Groups and Target Groups are different concepts.

Placement Groups are used when you want your application which is running on multiple instances inside a Placement Group to deliver high performance. This high performance is achieved by leveraging the placement of these instances, depending on the type of Placement Group ( Spread - if you want the instances to spread across an hardware, Partition - Spread across logical partitions, Cluster - packs instances inside AZ ) the instances will be placed. You would need this when you realize there is a lot of network latency (subsequent performance degradation) due to interdependence and in order to minimize this you would want to place the instances close to each other and use Placement Group.

Target Group on the other hand is used by an Application Load Balancer - When you create each listener rule while configuring Application Load Balancer, you specify a target group and conditions. When a rule condition is met, traffic is forwarded to the corresponding target group.

Inside each Target Group is a set of targets which are registered whose health are being monitored by the load balancer constantly.You can either specify Instance ID, IP Addresses or Lambda functions as these targets.

Nishant Sondhi
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  • Adding on to the fact that if an instance is a part of both target group and placement group, if you want to delete the Placement Group - you must first have to terminate all the instances in the Placement Group which will terminate our instance which is also the part of Target Group. – Nishant Sondhi Jun 24 '19 at 20:11