Placement Groups and Their Use

Welcome to this lesson on EC2 placement groups, a feature that appears frequently on AWS exams and is crucial for deploying groups of EC2 instances with specific performance or redundancy requirements. Placement groups let you control how instances are distributed across the AWS infrastructure to either maximize performance or enhance fault tolerance.

Imagine deploying a fleet of EC2 instances with one of the following scenarios:

All instances in the same availability zone for ultra-fast communication.
Instances spread across different availability zones for high redundancy.
A combination where clusters of systems are distributed over multiple availability zones (for example, replicating a database cluster across three availability zones in Virginia).

Placement groups provide a managed approach to deploying similar-function EC2 instances, optimizing your infrastructure for high-demand workloads or resiliency by controlling the physical placement on Amazon hardware.

Cluster Placement Group

A cluster placement group is optimized for low latency and high throughput workloads. It packs instances as closely as possible—typically within a single availability zone and even on the same physical server—to maximize network performance for high-performance computing, big data analytics, and applications requiring rapid inter-instance data exchanges.

The image describes the "Cluster Placement Group" type of EC2 instance placement, highlighting its benefits such as low latency, high throughput, and suitability for HPC, Big Data, and analytics workloads.

Using a cluster placement group helps leverage a high-speed network backbone, which is ideal for:

High-performance computing
Big data analytics
Machine learning applications

The image illustrates a "Cluster Placement Group" with benefits like low-latency network performance and high network throughput, featuring a diagram of interconnected nodes in the same rack.

The image outlines use cases for a Cluster Placement Group, including high-performance computing, big data analytics, and machine learning with GPU/FPGA.

Note

Keep in mind the following limitations when using a cluster placement group:

A limited number of instances per group.
Restricted to a single availability zone.
Network throughput is constrained by the slowest instance type.
Enhanced networking can help overcome some performance limits.
It is recommended to use uniform instance types along with the necessary capacity reservations.

The image lists limitations related to supported instances, single availability zones, network throughput, and enhanced networking, with a gradient blue background.

External traffic from a single machine is generally limited to around 5 Gbps, though using Direct Connect can boost this up to 100 Gbps. Note that cluster placement groups do not support mixed instance types.

The image is a comparison chart showing the pros and cons of a Cluster Placement Group, highlighting advantages like low latency and improved network performance, and limitations such as a single availability zone and capacity constraints.

Partition Placement Group

A partition placement group isolates instances by assigning them to distinct logical partitions, ensuring that instances in different partitions do not share the same underlying hardware. This approach isolates hardware failures, as each partition resides on its own set of racks with separate networking and power sources. It is an excellent choice for large-scale workloads such as distributed databases or high-availability applications.

The image describes the "Partition Placement Group" type of EC2 instance placements, highlighting features like instances spread across logical partitions, no shared hardware between partitions, and suitability for distributed or Hadoop-based workloads.

A partition placement group can span multiple racks within a single availability zone, offering failure isolation. For multi-AZ resilience, you can establish separate partition placement groups in each availability zone.

The image illustrates a "Partition Placement Group" in a cloud environment, showing instances distributed across three partitions within a single availability zone to isolate failures.

Key considerations for using partition placement groups:

Up to seven partitions per availability zone per region by default.
Instance limits vary depending on your account.
Dedicated instances support only two partitions.
Capacity reservations used for clusters cannot be applied to partition placement groups.

The image is a comparison chart showing the pros and cons of a Partition Placement Group. Pros include fault isolation, scalability, and improved fault tolerance, while cons include being confined to a single availability zone and added complexity.

Spread Placement Group

The spread placement group is designed for maximum isolation. Each instance is placed on distinct underlying hardware, reducing the risk that a single hardware failure will affect multiple instances. This configuration is ideal for mission-critical workloads that require high fault tolerance, such as highly available microservices or isolated virtual machines required for compliance.

The image illustrates a "Spread Placement Group" in a cloud computing context, showing instances distributed across different racks in three availability zones (us-east-1a, us-east-1b, us-east-1c) to reduce simultaneous failures.

Important details for spread placement groups:

Support up to seven instances per availability zone.
To deploy more instances, you must create multiple groups.
Dedicated instances are not supported.
Compared to cluster placement groups, the network performance may be lower due to greater separation of hardware.

The image outlines three use cases for a Spread Placement Group: minimizing simultaneous instance failure risks for critical workloads, ensuring high availability for microservices applications, and isolating virtual machines for compliance.

The image lists limitations related to AWS, including instance limits per availability zone, lack of support for dedicated instances, and specific conditions for AWS Outposts.

The image lists the pros and cons of a Spread Placement Group, highlighting high availability, fault tolerance, and multiple AZ support as advantages, and limited instances per AZ and reduced network optimization as disadvantages.

Comparison Overview

Each placement group type is tailored for specific infrastructure requirements:

Placement Group Type	Best For	Key Benefits
Cluster Placement Group	Low latency, high throughput workloads	Enhanced network performance, ideal for HPC and big data scenarios
Partition Placement Group	Fault-tolerant setups with hardware isolation	Isolation of hardware failures across partitions, suitable for distributed databases and high-availability apps
Spread Placement Group	Critical applications requiring maximum isolation	Maximum fault tolerance through isolated hardware, ideal for compliance and microservices

The image is a comparison table outlining different types of computing setups: Cluster, Partition, and Spread, along with their use cases and characteristics. It highlights aspects like low-latency workloads, fault-tolerant systems, and hardware isolation.

When deciding which placement group to use, consider:

Whether your priority is optimized network performance, enhanced fault tolerance, or strict hardware isolation.
The instance type uniformity and capacity reservations available.
Infrastructure requirements such as load, scalability, and cost efficiency.

The image outlines the benefits of choosing the right AWS Placement Group, including optimized network performance, enhanced fault tolerance, performance optimization, data distribution, and cost efficiency.

Thank you for reading this lesson. Understanding the differences between cluster, partition, and spread placement groups is essential to design a resilient, high-performance AWS infrastructure.

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