🔹 1. Cluster Placement Group
Goal: Achieve low-latency, high-throughput communication between instances.
✅ Use this when:
- You need fast communication between instances.
-
Your application is performance-sensitive and needs tightly-coupled computing, such as:
- High Performance Computing (HPC)
- Machine Learning Training
- Financial trading systems
- Video rendering
- Scientific simulations
🧠 How it works:
- All instances are placed very close together in the same Availability Zone (AZ) — same rack or neighboring racks.
- This gives high bandwidth and low network latency.
⚠️ Limitation:
- If there is a hardware failure or AZ issue, many instances may be affected — higher risk of correlated failure.
🔹 2. Partition Placement Group
Goal: Reduce risk of failure by isolating groups of instances on different hardware.
✅ Use this when:
- You're running large, distributed systems that replicate data across nodes.
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Examples include:
- Big Data tools: Hadoop, Spark
- Databases like Cassandra
- Streaming platforms like Kafka
🧠 How it works:
- Instances are split into logical partitions.
- Each partition is physically isolated — different racks, power sources, and network paths.
- No two partitions share the same hardware.
🔄 Benefits:
- If one partition fails, others remain unaffected.
- Allows for data replication and fault tolerance.
🔹 3. Spread Placement Group
Goal: Maximize high availability by putting each instance on completely separate hardware.
✅ Use this when:
- You have a small number of critical instances and want to minimize risk of simultaneous failure.
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Ideal for:
- Web servers
- Load balancers
- Domain controllers
- Application layer with few but crucial VMs
🧠 How it works:
- AWS ensures each instance is on different hardware, possibly across different racks or even AZs.
- Maximum of 7 instances per AZ in a Spread group.
🛡️ Strongest failure isolation.
🔍 Quick Decision Guide
| Scenario | Use this placement strategy |
|---|---|
| Fast communication between nodes | Cluster |
| Distributed app with fault tolerance needs | Partition |
| Few critical instances that must not fail together | Spread |
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