AWS Placement Group Strategy For Instances | Overview & Hands-On.

 

An overview & Hands-On for AWS Placement Group Strategy For Instances. 

Focus:

• Tailored for Devops, DevSecops & Cloud Engineers.

Breakdown:

• Intro,
• Cluster Placement Group,
• Partition Placement Group,
• Spread Placement Group,
• The concept: an AWS Placement Group,
• How to Create a Placement Group,
• How to Create a Placement Group: Using AWS Console,
• Benefits or aws placement groups & their risks,

• Use cases,

• Projects: Hands-On, 
• Recommendations.

Intro:

• AWS offers three placement group strategies—Cluster, Partition, and Spread.
• Each Strategy is suitable for different types of applications and fault tolerance requirements. 
• The choice of strategy affects how instances are physically distributed across underlying hardware within a data center or Availability Zone (AZ).
• Sometimes twtech wants control over its EC2 Instance  with placement strategy.
• That strategy is defined using the placement groups.
• When twtech creates a placement group, twtech may specify one of the following strategies for the group:

Cluster Placement Group

Strategy: 

• Packs instances close together on the same physical hardware in a single Availability Zone to achieve high network throughput and low latency.
• twtech instances have a low-latency group (Cluster) within a single Availability Zone.

Best For:

•  Applications that require high-performance computing (HPC), big data processing, or situations where inter-instance communication speed is critical.

Considerations:

•  All instances share the same racks, increasing the risk of a single hardware failure impacting all instances in the group.

Partition Placement Group

Strategy:

•  Spreads instances across different racks and partitions within an Availability Zone. 
• Each partition has its own power source and network, providing isolation from failures in other partitions. 
• AWS ensures no two partitions share the same underlying hardware.
• twtech instances are provision on different partitions (which rely on different sets of Racks) within an AZ.  
• twtech can scales up to 100s of its EC2 instances per group.

Best For:

•  Large distributed and replicated workloads like Hadoop, Cassandra, or Kafka. 
• It is ideal for systems that need both availability and scalability, allowing up to seven partitions per group in a single AZ.

Considerations:

•  Offers a balance of isolation and co-location, providing better fault tolerance than a Cluster group without the strict limitations of a Spread group. 

Spread Placement Group

Strategy:

•  Strictly places each instance on distinct, separate physical hardware to minimize correlated failures.
• twtech instances are  spread (Scattered) across underlying hardware (max 7 instances per group per AZ)

Best For: 

• Small groups of critical instances that need maximum fault tolerance, such as essential database servers, master nodes, or stateful applications.

Considerations:

•  Offers the highest level of isolation. It is limited to a maximum of seven running instances per group within a single Availability Zone.

For detailed documentation, refer to the AWS Placement Groups Guide

The concept: an AWS Placement Group

A Placement Group in AWS controls how EC2 instances are placed on underlying hardware for performance or availability goals. There are three types:

1. Cluster Placement Group:
• Packs instances close together in a single AZ.
• Best for high-performance workloads that need low latency and high network throughput (like HPC, big data).
2. Spread Placement Group:
• Spreads instances across different hardware racks.
• Best for high availability — if hardware fails, only one instance is affected.
3. Partition Placement Group:
• Divides instances into partitions, and each partition is isolated from the others (separate racks).
• Best for large, distributed systems like Hadoop, Kafka clusters.

 How to Create a Placement Group: Using AWS Console

1. Go to the EC2 Dashboard.
2. In the left menu, click Placement Groups under "Instances & Images."
3. Click Create placement group.
4. Enter:
• Name (must be unique within your account).
• Strategy (Cluster, Spread, or Partition).
• Number of partitions (only if twtech chooses Partition strategy).
5. Click Create.

Once created, when you launch an EC2 instance, twtech can select this Placement Group under Advanced settings.

 How to Create a Placement Group: Using AWS CLI

Create a twtech-Cluster placement group, for example:

#   bash

aws ec2 create-placement-group --group-name twtech-cluster-group --strategy cluster

or:

aws ec2 create-placement-group \

    --group-name twtech-cluster-group \

    --strategy cluster

Or a Spread placement group:

#  bash 

aws ec2 create-placement-group --group-name twtech-spread-group --strategy spread

or:

aws ec2 create-placement-group \

    --group-name twtech-spread-group \

    --strategy spread

Or a Partition placement group with 5 partitions:

#  bash

aws ec2 create-placement-group  --group-name twtech-partition-group \ 
--strategy partition --partition-count 5 

or:

aws ec2 create-placement-group \

    --group-name twtech-partition-group \

    --strategy partition \

    --partition-count 5 

Benefits or aws placement groups and their risks

Benefits of AWS Placement Groups

1. Improved Network Performance (Cluster)

• Super low latency and high throughput because instances are physically close.
• Ideal for applications like HPC (High Performance Computing), distributed databases, or big data analytics.

2. Higher Availability (Spread & Partition)

• Spread and Partition groups isolate instances across racks and hardware.
• If one server fails, the others continue running, improving fault tolerance.

3. Control Over Infrastructure Layout

• twtech gets more control over instance placement — which can help with compliance, performance tuning, and architecture decisions.

4. Scalability for Big Systems (Partition)

• Partition groups allow twtech to scale large distributed systems across multiple hardware partitions with minimal impact if a partition fails.

5. Optimized Resource Utilization

• Placement groups help maximize networking resources and optimize hardware usage, especially for tightly-coupled applications.

 Risks or Limitations of AWS Placement Groups

1. Instance Type Restrictions (Cluster)

• All instances must be in the same AZ and often the same instance type or family to achieve optimal performance.

2. Launch Failures

• In Cluster groups, if AWS doesn't have enough capacity in the AZ at that time, instance launches can fail.
• twtech might need to retry or use Capacity Reservations.

3. No Cross-AZ Placement

• Placement groups are AZ-scoped — twtech can't spread them across multiple AZs automatically. 
• Spread across AZs would be a manual architecture decision.

4. Harder Scaling in Cluster Groups

• Adding instances later can be tricky if there’s no more room in the physical hardware group (twtech might have to relaunch the group).

5. Cost Implications

• Placement groups themselves don't cost extra, but the instance types twtech typically use inside (like C5n, P4d, HPC instances) are premium-priced.

6. Design Complexity

• Managing Partition groups (like keeping track of partitions and mapping partitions to instance groups) adds complexity to system design.

7, Restricts number of instances per group/AZ:

·   NB:

•      twtech is permitted by AWS to have max 7 instances per group per AZ
•  twtech Tip to use cases:
• Use Cluster for high-speed communication (e.g., ML training, HPC).
• Use Spread for maximum fault tolerance (e.g., critical small apps).
• Use Partition for big distributed systems (e.g., HDFS, Cassandra, Kafka).

Project-1 : Hands-On.

Placement Groups:  Cluster

• How twtech uses AWS CLI to create a Cluster Placement Group,
• Make sure the terminal has aws CLI installed and configure.

#  bash

aws ec2 create-placement-group --group-name twtech-cluster-group --strategy cluster

• when twtech is subsequently  launching instances it reference that placement group already created: twtech-cluster-group

# bash

aws ec2 run-instances --image-id ami-12345678 --count 3 --instance-type c5n.18xlarge --placement GroupName=twtech-cluster-group

 Pros: 

• Great network (10 Gbps bandwidth between instances with Enhanced Networking enabled - recommended)

Cons: 

• However, If the AZ fails, all instances fails at the same time.

Use case:

•  Big Data job that needs to complete fast
• Application that needs extremely low latency and high network throughput.

Project-2: Hands-On.

Placement Groups:  Spread

• How twtech uses AWS CLI to create a Spread Placement Group,
• Make sure the terminal has aws CLI installed and configure.

#  bash

aws ec2 create-placement-group --group-name twtech-spread-group --strategy spread

when twtech is subsequently  launching instances it reference that placement group already created: twtech-spred-group

#  bash

aws ec2 run-instances --image-id ami-12345678 --count 3 --instance-type t3.medium --placement GroupName=twtech-spread-group

Summary table:

Strategy	Focus	Good for
Cluster	Performance & Low Latency	HPC, big data, ML
Spread	Fault Tolerance	Critical apps needing maximum uptime

 Pros:

•  They can be provisioned across Availability Zones (AZ)
•  This spread of instances across AZ , reduced the risk to simultaneous failure.
•  EC2 Instances are spread across  different physical hardware.

 Cons:

•  Limited to 7 instances per AZ per placement group

Use case:

•  Application that needs to maximize high availability
•  Critical Applications where each instance must be isolated from failure from each other.

Project-3: Hands-On.

Placements Groups:  Partition

• How twtech uses AWS CLI to create a Partition Placement Group,
• Make sure the terminal has aws CLI installed and configure.

#  bash 

aws ec2 create-placement-group --group-name twtech-partition-group --strategy partition --partition-count 3

• Here, twtech is asking AWS to make 3 partitions.
• when twtech is subsequently  launching instances it reference that placement group already created: twtech-partition-group

#  bash

aws ec2 run-instances --image-id ami-12345678 --count 6 --instance-type m5.large --placement GroupName=twtech-partition-group

NB:

• AWS automatically places instances into partitions, or you can manually specify.
• Up to 7 partitions per AZ
•  Provisioned across multiple AZs in the same region
•  An AZ can host up to 100 EC2 instances
•  The instances in a partition do not share racks with the instances in the other partitions
• A partition failure can affect many EC2 but won’t affect other partitions
•  EC2 instances get access to the partition information as metadata

Use cases: 

• special for : HDFS, HBase, Cassandra, Kafka

twtech-Summary Table - All Three Types stategies:

Strategy	Focus	Use Case
Cluster	Low Latency, High Throughput	HPC, ML training, Big Data
Spread	Max Fault Tolerance	Critical small apps (<=7 instances)
Partition	Isolate failure domains	Large distributed systems

twtech Recommendations:

• Kafka brokers: m5.xlarge, m5.2xlarge, i3.xlarge
• HBase Masters/RegionServers: r5.xlarge, r5.2xlarge
• Cassandra nodes: r6i.xlarge, r6g.xlarge
• HDFS datanodes: i3.xlarge, i3en.xlarge (if twtech needs super storage throughput)

Important:

• When twtech uses a placement group (cluster strategy), AWS tries to put all the instances close together on the network.
• So choosing fast network-enabled instances is critical (at least 10 Gbps networking).

Project: Hands-On:

• How twtech creates  Placement  Group strategies for its instances using the console.

Step-1:

• Go to aws ec2 services console , and navigate to Placement Groups (under Network & Security)

Step-2:

• Click on Create placement group

• Assign a name for the placement group: twtech-placement-group
• Select a strategy for the placement group: Cluster.
• Instances are very close to each other, with maximum stability and communication.
• Name: twtech-placement-group-cluster
• Strategy: Cluster

• Create Placement group

Step-3:

• twtech follows the same approach to create a placement group with Spread strategy.
• This strategy allows instances to be distributed as much as possible.
• Name: twtech-placement-group-spread
• Strategy:  Spread
• Allow the spread level to default: Rack (No restrictions)

Next,

• twtech creates a placement group with:  Partition Strategy

• Name: twtech-placement-group-partition
• Strategy:  Partition
• Choose number of partitions between:  1-7
• twtech partitions choice for this project:  5 

Step-4:

• twtech launches instances and reference the already create strategy that fits the need.
• Launch instance

• Select key.pair or create one ( if instance would subsequently need ssh login)

• Select the security group: Allowing only the need port to internet access

Step-5:

• Go to Advanced details and navigate down to, Placement group:
• Select the placement group of that fits the context from the  strategies initially created.

• Launch instance:

Step-6:

• How twtech Troubleshoots wrong choice of instance.
•  check the list of supported instances below.

NB:

twtech analysis of the error: explained

• "Cluster placement groups are not supported by the 't2.medium' instance type".
• This means twtech tried launching a t2.medium instance inside a placement group with strategy = cluster.
•  However t2.medium does not support cluster placement groups.
•   "cluster"  placement group need instances for need low-latency networking.

twtech Solutions:

• Option 1: Use an instance type that support cluster placement groups — like c5, m5, r5, c6g, etc. (Basically, newer, compute-optimized or network-optimized families.)
• Option 2: Remove (change) or try another placement group that support t2.medium from the instance launch configuration (if twtech must use t2.medium).

Step-7:

• twtech Edits instance configurations: 
• From:  t2.medium (which was not supported)

To : c5.large (that supports the placement group and most importancely, fit the purpose)

 Step-8:

• twtech try launching the instance again after editing configuration.
• successfully, twtech has launched instances to a specified aws placemen-group ( existing or created)

twtech-insights

•   Supported families of instances for placement groups: C, M, R, P, G, H, I, Inf, D, F, etc.
•  Unsupported families of instances for placement groups: T (like t2.medium, t3.micro, etc.) because they're burstable (with high CPU utilization/spikes),  and not high-performance.