AWS Placement Group Strategy for Instances: Cluster, Spread, Partition.

 

Concepts & Projects.

The Placement Groups

• Sometimes twtech wants control over its EC2 Instance  with placement strategy.

• That strategy can be defined using placement groups.

• When twtech creates a placement group, twtech may specify one of the following strategies for the group:

• Cluster strategy: twtech-placement-group-clusters instances have a low-latency group in a single Availability Zone.

• Spread strategy: twtech-placement-group-spreads instances are  spread across underlying hardware (max 7 instances per group per AZ)

• Partition strategy: twtech-placement-group-partition 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.

AWS Placement Groups and how twtech creates them.

let's break this down simply:

What is 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.

Using AWS CLI:

Create a 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 3 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 (you 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:

·        max 7 instances per group per AZ

 twtech Tip:

• 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).

Placement Groups: Cluster

Placement Groups:  Cluster strategy

A Placement Group is a way to control how Amazon EC2 instances are placed on the underlying hardware to meet specific needs like high availability, low network latency, or high throughput.

There are three types of placement strategies:

1. Cluster
2. Spread
3. Partition

Cluster Placement Group specifically means:

• Instances are physically close together on the same rack or very nearby racks in a single Availability Zone.
• Very low network latency and high network throughput between instances.
• Ideal for workloads that need high-performance computing (HPC) or big data jobs where speed of communication between servers is critical.

Key points about Cluster:

• All instances must be launched in the same AZ (Availability Zone).
• Best for applications that benefit from very fast communication — like distributed databases, ML training, or HPC applications.
• There’s a higher risk: if the rack fails, all instances could fail at once (because they’re so close together).

Example AWS CLI to create a Cluster Placement Group:

#  bash

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

Then, when launching instances, you reference that placement 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: 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.

Placement Groups:  Spread

Placement Groups:  Spread strategy

A Spread Placement Group means:

• Instances are placed on different racks, with separate power, networking, and hardware.
• Each instance is isolated from the others to reduce the risk of simultaneous failure.
• Best for high availability and resilience — if one rack has an issue, only one instance is affected.

Key points about Spread:

• Great for critical applications where you can’t afford multiple instance failures at the same time.
• You can have up to 7 running instances per Availability Zone in a single spread group.
• It's more about reliability than about fast network speed.
• Works across multiple AZs if you want, but typically it's per AZ.

Example AWS CLI to create a Spread Placement Group:

#  bash

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

When launching instances into it:

#  bash

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

Summary - Quick View:

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.

Placements Groups:  Partition

Now about Placement Groups — Partition strategy:

A Partition Placement Group is designed for large distributed applications like Hadoop, Kafka, or Cassandra, where you need many instances but still want to reduce correlated failures.

How it works:

• Instances are divided into partitions.
• Each partition is isolated from the others — different racks, different hardware, etc.
• Within a partition, instances may share racks.
• If one partition fails (e.g., power or network issue), only that partition’s instances are impacted, not the whole group.

Key points about Partition:

• Best for large, scalable, distributed workloads.
• You control how many partitions you want (AWS lets you pick the number when you create it).
• Supports hundreds of instances (way bigger than Spread groups).
• Each partition can span different hardware — to limit failure domains.

Example AWS CLI to create a Partition Placement Group:

#  bash 

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

(Here, you’re asking AWS to make 3 partitions.)

When launching instances:

#  bash

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

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 Concrete 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 you need super storage throughput)

Important:
When you use 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:

How twtech creates  Placement  Group strategies for its instances

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

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

Also follow 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)

Then, create 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 

Go to Advanced details and navigate down to, Placement group name:

Select the placement group of choice from exiting strategies already created or create one.

Launch instance:

Troubleshooting wrong choice of instance: check the list of supported instances below.

The error

"Cluster placement groups are not supported by the 't2.medium' instance type"
means twtech tried launching a t2.medium EC2 instance inside a placement group with strategy = cluster, but t2.medium does not support placement groups (especially "cluster" ones that need low-latency networking).

Solutions:

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

Edit instance configurations: 

From:  t2.medium 

To : c5.large

 successfully, twtech has launched instances to a specified aws placemen-group ( existing or created)

twtech-insights

      *   Supported families: C, M, R, P, G, H, I, Inf, D, F, etc.

      *  Unsupported families: T (like t2.medium, t3.micro, etc.) because they're burstable,  and not high-performance