EC2 placement groups are logical groupings of instances that influence how they are placed on underlying hardware to meet specific workload requirements. There are three types of placement groups in AWS.
**Cluster Placement Groups** place instances close together within a single Availability Zone.…EC2 placement groups are logical groupings of instances that influence how they are placed on underlying hardware to meet specific workload requirements. There are three types of placement groups in AWS.
**Cluster Placement Groups** place instances close together within a single Availability Zone. This configuration provides low-latency network performance with high throughput, making it ideal for High Performance Computing (HPC) applications, big data workloads, and applications requiring tight coupling between nodes. 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 to reduce correlated failures. Each instance is placed on a separate rack with its own network and power source. You can have a maximum of 7 running instances per Availability Zone per group. This strategy suits critical applications where individual instance isolation is essential for high availability.
**Partition Placement Groups** divide instances into logical partitions, ensuring that each partition does not share underlying hardware with other partitions. Each partition resides on separate racks. You can have up to 7 partitions per Availability Zone. This approach benefits large distributed workloads like Hadoop, Cassandra, and Kafka where you need to minimize the impact of hardware failures while maintaining large-scale deployments.
**Key Considerations for SysOps Administrators:**
- Placement groups are free to create
- Instance types should be homogeneous within cluster placement groups for optimal performance
- You cannot merge placement groups
- Instances can be moved into placement groups when stopped
- Placement group names must be unique within your AWS account
- Not all instance types support all placement group strategies
When provisioning infrastructure through automation tools like CloudFormation or AWS CLI, you can specify placement group configurations to ensure consistent deployment patterns that align with your applications performance and availability requirements.
EC2 Placement Groups - Complete Guide for AWS SysOps Administrator Associate
What are EC2 Placement Groups?
EC2 Placement Groups are logical groupings of instances within a single Availability Zone or across multiple Availability Zones that influence how instances are placed on underlying hardware. They enable you to control the EC2 instance placement strategy to meet your workload requirements.
Why are Placement Groups Important?
Placement groups are critical for: • High-performance computing (HPC) workloads requiring low latency • Big data applications needing high network throughput • Distributed databases requiring fault isolation • Mission-critical applications needing hardware-level redundancy
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 • Ideal for HPC applications, big data jobs, and applications requiring high network throughput • All instances should be launched at the same time for best results • Supports Enhanced Networking • Risk: If the rack fails, all instances fail simultaneously
2. Spread Placement Groups • Places instances on distinct underlying hardware (separate racks) • Each rack has its own network and power source • Can span multiple Availability Zones within the same Region • Limitation: Maximum of 7 running instances per Availability Zone per group • Ideal for applications with a small number of critical instances that must be kept separate • Reduces the risk of simultaneous failures
3. Partition Placement Groups • Divides instances into logical segments called partitions • Each partition is placed on separate racks (distinct hardware) • Can have up to 7 partitions per Availability Zone • Can span multiple Availability Zones in the same Region • Scales to hundreds of instances per group • Ideal for large distributed and replicated workloads like HDFS, HBase, and Cassandra • Instances can access partition information as metadata
How Placement Groups Work
Creating a Placement Group: 1. Specify a unique name for your placement group 2. Choose the placement strategy (cluster, spread, or partition) 3. For partition groups, specify the number of partitions 4. Launch instances into the placement group
Key Behaviors: • An instance can only belong to one placement group at a time • You cannot merge placement groups • You can move an existing instance into a placement group (instance must be stopped first) • Placement groups are free to create • Recommended to use the same instance type within a cluster placement group
Limitations and Constraints
• Cluster placement groups cannot span multiple Availability Zones • Spread placement groups have a limit of 7 instances per AZ • Partition placement groups have a limit of 7 partitions per AZ • Certain instance types may not be supported in placement groups • Insufficient capacity errors can occur if launching instances in an existing cluster placement group
Best Practices
• Use a single launch request to launch all required instances in a cluster placement group • Use homogeneous instance types within cluster placement groups • If capacity errors occur, stop and restart all instances in the cluster placement group • Enable Enhanced Networking for best performance in cluster placement groups
Exam Tips: Answering Questions on EC2 Placement Groups
When you see scenarios about:
• Low latency and high throughput between instances → Think Cluster Placement Group • HPC, big data analytics, or machine learning workloads → Think Cluster Placement Group • Critical instances that need hardware isolation → Think Spread Placement Group • Small number of instances needing maximum availability → Think Spread Placement Group • Large distributed databases like Cassandra or HDFS → Think Partition Placement Group • Workloads needing topology awareness → Think Partition Placement Group
Remember these key numbers: • Spread: Maximum 7 instances per AZ • Partition: Maximum 7 partitions per AZ
Common Exam Traps: • Cluster placement groups are single-AZ only • You must stop an instance before moving it to a placement group • Capacity errors in cluster groups are resolved by stopping and restarting all instances • Spread groups provide instance-level isolation while partition groups provide partition-level isolation