An architect must run 5 critical instances of a distributed application in a single Availability Zone. Each instance must run on genuinely distinct underlying hardware, so that a single hardware failure cannot affect more than one instance. Which EC2 placement group strategy fits this requirement?
- Spread placement group
- Cluster placement group
- Partition placement group
- No placement group, relying on AWS's default instance placement
Correct answer: A. Spread placement group
A Spread placement group strictly places each instance on distinct underlying hardware, each with its own separate power source and network path, and it supports up to 7 running instances per group per Availability Zone, which is exactly the level of per-instance hardware isolation this scenario needs for a small number of critical instances. A Cluster placement group instead packs instances close together within a single Availability Zone to minimise network latency and maximise throughput, which increases rather than decreases the chance that a single hardware or rack failure affects multiple instances. A Partition placement group divides instances into a smaller number of partitions, where each partition can contain many instances, and is designed for large distributed systems such as Hadoop, Cassandra, or Kafka that can tolerate losing an entire partition, not for guaranteeing per-instance isolation among only 5 critical instances. Relying on AWS's default placement gives no guarantee about hardware separation at all, leaving the outcome entirely up to AWS's internal placement decisions.
Source: AWS EC2 documentation: Placement groups — spread placement groups