AWS Placement Groups  - EC2 Service

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Pintu Patra
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Placement Groups in AWS allow you to control how instances are placed on the underlying physical hardware to optimize performance, availability, and fault tolerance. There are three main types of placement groups:

1. Cluster Placement Group

  • Purpose: Places instances close together within a single Availability Zone (AZ) for low-latency, high-bandwidth networking.

  • Use Case: High-performance computing (HPC), large databases, and applications requiring low-latency communication.

  • Key Points:

    • High Performance: Best for workloads needing high throughput and low latency.

    • Risk: If the AZ fails, all instances in the group are affected.

    • Instance Compatibility: Not all instance types (e.g., t2, t3) are supported.

    • Limitations: Only works in a single AZ.

2. Spread Placement Group

  • Purpose: Distributes instances across multiple physical servers to reduce the risk of correlated failures.

  • Use Case: Applications requiring high availability and fault tolerance but not necessarily low-latency communication between instances.

  • Key Points:

    • Fault Tolerance: Spread across multiple physical hardware, reducing the impact of failures.

    • Instance Limit: Maximum of 7 instances per AZ.

    • Best For: Stateless applications, web servers, distributed systems.

3. Partition Placement Group

  • Purpose: Instances are grouped into logical partitions, with each partition placed on separate hardware to reduce failure risks.

  • Use Case: Large distributed applications like Hadoop, Cassandra, or large-scale databases.

  • Key Points:

    • Fault Isolation: Protects against failures by isolating instances into separate partitions.

    • Scalability: Supports thousands of instances across multiple partitions.

    • Best For: Big data systems, distributed databases.

General Key Points

  • Availability Zones: Cluster groups work within a single AZ, while Spread and Partition groups can span multiple AZs.

  • Instance Types: Ensure compatibility of the instance type with the desired placement group type.

  • Limitations: Placement groups have restrictions on the number of instances and types of workloads.

Best Practices

  • Cluster: Use for low-latency, high-throughput workloads like HPC.

  • Spread: Use for applications needing high availability and fault tolerance, with instances spread across physical hardware.

  • Partition: Best for large-scale distributed systems like big data and databases, where fault isolation is key.

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