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EC2 Placement Groups: Fine-Tuning Your Cloud Infrastructure for Specific Workload Needs

Hello, Dev Community!

Amazon EC2
Amazon Web Services' Elastic Compute Cloud (EC2) is one of the most popular offerings in the AWS ecosystem. As an Infrastructure as a Service (IaaS) platform, EC2 provides users with the ability to:

  • rent virtual machines (EC2)

  • store data on virtual drives(EBS)

  • distribute loads across machines(ELB)

  • scale services using auto-scaling groups.(ASG)

Sometimes you want to exert more control over the EC2 instance placement strategy within the AWS infrastructure.
We don't get direct interaction with the hardware of AWS, but we let AWS know how we would like our EC2 instance to be placed compared to one another.
That strategy can be defined using placement groups.

Placement groups allow you to define a strategy for how EC2 instances should be arranged within the AWS infrastructure.When you create a placement group, you specify one of the following 3 strategies for the group:

  • Cluster

  • Spread

  • Partition

Cluster Placement Group

Cluster
Pack instances close together inside an Availability Zone. This strategy enables workloads to achieve the low-latency network performance necessary for tightly coupled node-to-node communication that is typical of high-performance computing (HPC) applications.
Pros: Great network (10 Gbps bandwidth between instances with
Enhanced Networking enabled - recommended)
Cons: If the AZ fails, all instances fails at the same time
• Use case:

  1. Big Data job that needs to be completed fast

  2. Applications that need extremely low latency and high network throughput

Spread Placement Group

Spread
Strictly places a small group of instances across distinct underlying hardware to reduce correlated failures

Pros:

  1. Can span across Availability Zones (AZ)

  2. Reduced risk is simultaneous failure

  3. EC2 Instances are on different physical hardware

Cons:
Limited to 7 instances per AZ per placement group

• Use case:

  1. Application that needs to maximize high availability

  2. Critical Applications where each instance must be isolated
    from failure from each other

Partition Placement Group

Partition
Spreads your instances across logical partitions such that groups of instances in one partition do not share the underlying hardware with groups of instances in different partitions.

• You can have up to 7 partitions per AZ
• Can span across multiple AZs in the same region
• Up to 100s of EC2 instances
• The instances in a partition do not share racks with the instances
in the other partitions
• A partition failure can affect many EC2 but won’t affect other
partitions
• EC2 instances get access to the partition information as metadata
• Use cases: Big data applications which are partition aware such as
HDFS, HBase, Cassandra, Kafka

These strategies enable you to tailor the placement of your instances to meet specific performance, availability, and fault tolerance requirements.

To wrap up,

  • Placement groups are optional. If you don't specify a placement group, EC2 will attempt to place instances in a way that minimises correlated failures across underlying hardware.

  • There's no charge for creating a placement group itself.

  • Each instance can only be placed in one placement group at a time.

  • You can't merge placement groups once they're created.

  • You can't launch Dedicated Hosts in placement groups.

  • You can't launch a Spot Instance that is configured to stop or hibernate on interruption in a placement group.

By understanding and utilising EC2 placement groups effectively, you can optimise your cloud infrastructure to better suit your specific workload needs, whether you're dealing with high-performance computing, distributed applications, or mission-critical systems requiring enhanced fault tolerance.

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