EC2 placement groups are logical groupings of instances that influence how AWS places them on underlying hardware, enabling you to optimize for specific workload requirements. There are three types of placement groups available in AWS.
**Cluster Placement Groups** position instances close together…EC2 placement groups are logical groupings of instances that influence how AWS places them on underlying hardware, enabling you to optimize for specific workload requirements. There are three types of placement groups available in AWS.
**Cluster Placement Groups** position instances close together within a single Availability Zone. This configuration delivers low-latency, high-throughput network performance between instances, making it ideal for tightly-coupled HPC applications, big data workloads, and applications requiring high network throughput. Instances benefit from enhanced networking capabilities and can achieve up to 10 Gbps bandwidth between instances.
**Spread Placement Groups** distribute instances across distinct underlying hardware, reducing the risk of simultaneous failures. Each instance runs on separate racks with independent network and power sources. You can have a maximum of seven running instances per Availability Zone per group. This strategy suits applications where instance isolation is critical, such as databases or applications requiring high availability.
**Partition Placement Groups** divide instances into logical partitions, where each partition resides on separate racks. Unlike spread groups, partitions can contain multiple instances. You can create up to seven partitions per Availability Zone. This approach works well for large distributed workloads like Hadoop, Cassandra, and Kafka, where you need to contain failure impact while maintaining scalability.
**Key Considerations for Solutions Architects:**
- Placement groups are free to use
- Instances should be launched simultaneously for optimal placement in cluster groups
- Homogeneous instance types are recommended within cluster placement groups
- Existing instances can be moved into placement groups when stopped
- Placement groups cannot span multiple regions
- Cluster placement groups cannot span multiple Availability Zones
When designing for continuous improvement, evaluate your applications network and availability requirements to select the appropriate placement strategy, balancing performance optimization against fault tolerance needs.
EC2 Placement Groups: Complete Guide for AWS Solutions Architect Professional
Why EC2 Placement Groups Are Important
EC2 Placement Groups are critical for optimizing workload performance, availability, and cost efficiency in AWS. Understanding placement groups is essential for the AWS Solutions Architect Professional exam because they directly impact how you design solutions for high-performance computing, distributed systems, and fault-tolerant architectures.
What Are EC2 Placement Groups?
Placement groups are logical groupings of EC2 instances that influence how instances are placed on underlying hardware. AWS offers three types of placement groups:
1. Cluster Placement Groups - Packs instances close together inside a single Availability Zone - Provides low-latency, high-throughput network performance - Best for HPC applications, big data jobs, and applications requiring high network throughput - All instances should be launched simultaneously for best results - Recommended to use enhanced networking and same instance types
2. Spread Placement Groups - Places instances on distinct underlying hardware - Reduces correlated failures by spreading instances across racks - Limited to 7 running instances per Availability Zone per group - Can span multiple Availability Zones within the same region - Ideal for critical applications requiring maximum availability
3. Partition Placement Groups - Spreads instances across logical partitions - Each partition has its own set of racks with independent network and power - Supports up to 7 partitions per Availability Zone - Can have hundreds of instances per partition - Best for large distributed workloads like HDFS, HBase, and Cassandra
How Placement Groups Work
When you create a placement group, you specify the strategy (cluster, spread, or partition). AWS then uses this strategy to determine instance placement:
- Cluster: AWS places all instances on high-bisection bandwidth hardware within the same rack or nearby racks - Spread: AWS ensures each instance runs on distinct hardware, with each rack having its own network and power source - Partition: AWS divides the group into partitions and ensures instances in different partitions do not share underlying hardware
Key Characteristics and Limitations
- Placement group names must be unique within your AWS account for a region - You cannot merge placement groups - An instance can only belong to one placement group at a time - Existing instances can be moved into a placement group only when stopped - Cluster placement groups cannot span Availability Zones - Spread and partition placement groups can span multiple Availability Zones - Dedicated instances can be launched into placement groups but may have limitations
Exam Tips: Answering Questions on EC2 Placement Groups
Scenario Recognition: - Low latency, high throughput requirements = Cluster Placement Group - Critical instances that must be isolated from failures = Spread Placement Group - Large-scale distributed databases or big data workloads = Partition Placement Group
Common Exam Traps: - Remember the 7-instance limit per AZ for Spread placement groups - Cluster placement groups are single-AZ only - Insufficient capacity errors occur when launching instances incrementally in cluster groups
Best Practice Indicators: - Questions mentioning HPC, MPI, or tightly-coupled workloads point to Cluster - Questions about rack-level isolation or critical application redundancy point to Spread - Questions about Hadoop, Kafka, or Cassandra typically point to Partition
Key Decision Points: - If the question emphasizes network performance over availability = Cluster - If the question emphasizes failure isolation for individual instances = Spread - If the question emphasizes failure isolation for groups of instances = Partition
Remember: The exam often presents scenarios where you must balance performance requirements against availability needs. Always identify whether the priority is speed, fault tolerance, or large-scale distributed processing before selecting your answer.