AWS Network & Security { Part - III }

AWS Network & Security { Part - III }


7 min read

What is a Placement Group in AWS EC2?

  • Definition : A placement group is a logical grouping of instances within a single Availability Zone. It is used to control the placement of instances to meet specific needs.

  • Purpose : Designed to provide low-latency network performance necessary for tightly-coupled node-to-node communication typical of high-performance computing (HPC) applications.

Key Features of Placement Groups

  • High Network Throughput : Enhanced network performance with low latency.

  • Single Availability Zone : Instances are placed within the same AZ to minimize network latency.

  • Types :

    • Cluster Placement Group : Groups instances into a low-latency network for high-performance applications.

    • Partition Placement Group : Spreads instances across logical partitions to reduce the impact of hardware failures.

    • Spread Placement Group : Distributes instances across distinct underlying hardware to reduce correlated failure risks.

How Placement Groups Work

Cluster Placement Group

  • Network Proximity : Instances are placed in close network proximity within a single AZ to ensure low-latency and high-throughput communication.

  • Enhanced Networking : Supports enhanced networking, providing higher packet per second (PPS) performance, lower network jitter, and lower latencies.

  • Optimized for HPC : Ideal for applications requiring high inter-node communications, such as parallel computations and tightly coupled computing tasks.

Partition Placement Group

  • Logical Partitions : Divides instances into partitions, each having its own set of hardware, minimizing the risk of correlated hardware failures.

  • Fault Isolation : Ensures that if one partition fails, instances in other partitions remain unaffected, providing a robust fault-tolerant environment.

  • Large Scale Deployment : Suitable for large distributed and replicated workloads, such as HDFS, HBase, and Cassandra, where data and compute resources need to be partitioned and distributed across multiple nodes.

Spread Placement Group

  • Hardware Redundancy : Distributes instances across distinct hardware racks within an AZ to minimize simultaneous hardware failures.

  • High Availability : Ensures that each instance runs on separate underlying hardware, providing high availability and minimizing the risk of correlated failure.

  • Critical Workloads : Suitable for small-scale critical applications that require individual instances to be isolated from failures of other instances, such as microservices and other small-scale fault-sensitive applications.

Creating a Placement Group

  1. Open the Amazon EC2 console.

  2. Navigate to "Placement Groups" in the left-hand menu.

  3. Provide a name and select the placement strategy (Cluster, Spread, Partition).

  4. Click "Create group".

Attaching a Placement Group to an Instance

  1. Attaching During Instance Launch

    1. Navigate to EC2 Dashboard :

      • Open the Amazon EC2 console.

      • Click on "Launch Instance".

    2. Instance Details :

      • On the "Choose an Amazon Machine Image (AMI)" page, select your desired AMI.

      • On the "Choose an Instance Type" page, select your instance type.

      • Click "Next: Configure Instance Details".

    3. Advance Details :

      • In the "Advance Details" page, locate the "Placement group" section.

      • Click on the "Add to placement group" dropdown.

      • Select the placement group you want to attach the instance to, or create a new placement group by clicking "Create new placement group" and entering the required details.

      • As shown in above snip, We just created this Cluster Group placement group.

      • Complete the remaining instance configuration steps and launch the instance.

  2. Attaching an Existing Instance to a Placement Group

    1. Stop the Instance :

      • Navigate to the "Instances" section in the EC2 console.

      • Select the instance you want to add to the placement group.

      • Click "Instance State" and select "Stop".

    2. Modify the Instance Placement :

      • With the instance still selected, click on "Actions", then "Instance Settings", and choose "Modify instance Placement".

      • In the "Modify instance Placement" dialog box, select the placement group from the dropdown menu.

      • Click "Save" and then start the instance.

Best Practices for Placement Groups

  • Cluster Placement Group :

    • Use Identical Instance Types : To achieve the best network performance, use instances of the same type and size.

    • Homogeneous Environment : Ensure the same AMI, instance type, and network configurations to avoid compatibility issues.

    • Capacity Reservations : Consider reserving capacity in advance, especially for large clusters, to ensure the availability of the required resources.

  • Partition Placement Group :

    • Optimize for Data Replication : Use for applications like HDFS and HBase that can benefit from distributed data across partitions.

    • Balance Partitions : Distribute workloads evenly across partitions to maximize fault tolerance and performance.

    • Monitor Health : Regularly monitor the health of each partition to proactively address issues before they impact the entire group.

  • Spread Placement Group :

    • Critical Small-Scale Deployments : Use for critical small-scale applications that cannot afford simultaneous failures.

    • Instance Distribution : Ensure instances are spread across multiple hardware racks to avoid correlated failures.

    • Resource Planning : Plan for capacity in advance, as spread placement groups have strict limits on the number of instances.

  • General Best Practices :

    • Early Planning : Plan placement group strategy early in the design phase of your application to align with performance and availability requirements.

    • Performance Testing : Conduct performance tests to validate that the chosen placement group strategy meets your application needs.

    • Automated Scaling : Use AWS Auto Scaling with placement groups to maintain optimal performance and availability as demand changes.

    • Regular Monitoring : Utilize AWS CloudWatch and other monitoring tools to keep track of the performance and health of instances within placement groups.

    • Compliance with Limits : Be aware of and comply with AWS service limits related to placement groups, such as the maximum number of instances per group.

    • Redundancy and Backup : Ensure that you have redundancy and backup plans in place, particularly since placement groups are limited to a single AZ.

Use Cases

  • High-Performance Computing (HPC) : Applications requiring high throughput and low latency, such as scientific simulations, financial modeling, and machine learning.

    • Example : Molecular dynamics simulations that need rapid communication between nodes.
  • Big Data : Workloads that need fault tolerance and data distribution, such as Hadoop clusters.

    • Example : Data analytics platforms processing large datasets across multiple nodes.
  • Distributed Databases : Databases that benefit from reduced failure domains and high availability, like Cassandra and MongoDB.

    • Example : A distributed database setup for an e-commerce platform ensuring data redundancy and high availability.
  • Web Applications : Large-scale applications requiring high availability and redundancy.

    • Example : A social media platform needing low-latency data access and high fault tolerance.
  • Financial Services : Applications needing fast transaction processing and real-time analytics.

    • Example : Real-time fraud detection systems that require low-latency data processing.
  • Content Delivery Networks (CDN) : Ensuring high availability and low latency for content distribution.

    • Example : Video streaming services requiring fast, reliable access to large media files.

Pros and Cons


  • Improved Network Performance : Placement groups, especially cluster placement groups, offer low latency and high throughput, which is ideal for HPC and other performance-intensive applications.

  • Fault Isolation : Partition and spread placement groups provide fault isolation, reducing the risk of simultaneous failures impacting all your instances.

  • Scalability : Placement groups allow for scaling your applications efficiently within the designed framework.

  • Flexibility : Different types of placement groups offer flexibility for various use cases, from low-latency clustering to fault-tolerant spreading.


  • Single Availability Zone : All placement group types operate within a single AZ, which can be a limitation for disaster recovery strategies.

  • Instance Type Limitations : Certain instance types and sizes might not be supported or available in placement groups.

  • Capacity Constraints : Depending on the type and size of the placement group, you might face capacity constraints which can delay instance launches.

  • Complexity in Management : Managing placement groups effectively requires understanding their limitations and best practices, which can add complexity.


  • Strategic Resource Allocation : Placement groups in AWS EC2 allow for strategic allocation of resources to meet specific performance and availability needs.

  • Versatility : With options for clustering, partitioning, and spreading instances, they cater to various use cases from high-performance computing to highly available web services.

  • Implementation Ease : Creating and managing placement groups is straightforward through the AWS Management Console, CLI, or SDKs, making them accessible for diverse application requirements.

  • Balanced Approach : While placement groups offer significant advantages in network performance and fault tolerance, they also come with limitations and potential complexities that need careful consideration during implementation.


Did you find this article valuable?

Support Chandra Prakash Reddy by becoming a sponsor. Any amount is appreciated!