Sometimes you want control over the EC2 Instance placement strategy That strategy can be defined using placement groups
When you create a placement group, you specify one of the following strategies for the group:
- Cluster — clusters instances into a low-latency group in a single Availability Zone
- Spread — spreads instances across underlying hardware (max 7 instances per group per AZ) – critical applications
- Partition — spreads instances across many different partitions (which rely on different sets of racks) within an AZ. Scales to 100s of EC2 instances per group (Hadoop, Cassandra, Kafka)