Placement Groups

Create and manage spread and cluster placement groups to control how Spinifex places EC2 instances across physical hosts for fault isolation or low latency.

ec2placementspreadcluster

Overview Prerequisites Troubleshooting

Overview

Placement groups control how Spinifex distributes instances across physical hosts. Two strategies are supported:

Spread — One instance per physical host, maximising fault isolation
Cluster — All instances on the same host, minimising latency

The partition strategy is not supported.

Supported operations:

create-placement-group — Create a new group
describe-placement-groups — Query groups with optional filters
delete-placement-group — Remove an empty group

Prerequisites

A running Spinifex cluster (see Setting Up Your Cluster)
AWS CLI configured with the spinifex profile:

bash

export AWS_PROFILE=spinifex

Create

bash

aws ec2 create-placement-group \
  --group-name my-spread-group \
  --strategy spread

bash

aws ec2 create-placement-group \
  --group-name my-cluster-group \
  --strategy cluster

Launch Into a Placement Group

bash

aws ec2 run-instances \
  --image-id $SPINIFEX_AMI \
  --instance-type t3.small \
  --key-name spinifex-key \
  --placement GroupName=my-spread-group \
  --count 3

Describe

bash

aws ec2 describe-placement-groups
aws ec2 describe-placement-groups --group-names my-spread-group
aws ec2 describe-placement-groups --group-ids pg-abc123
aws ec2 describe-placement-groups \
  --filters Name=strategy,Values=spread

Delete

The group must have no running instances before it can be deleted:

bash

aws ec2 terminate-instances --instance-ids $INSTANCE_ID
aws ec2 delete-placement-group --group-name my-spread-group

Troubleshooting

InsufficientInstanceCapacity Error

Not enough distinct physical hosts for a spread launch. Reduce --count or terminate existing instances to free host slots:

bash

spx admin nodes list

Cannot Delete Placement Group

The group still has running instances. Terminate them first:

bash

aws ec2 describe-instances \
  --filters Name=placement-group-name,Values=my-spread-group
aws ec2 terminate-instances --instance-ids $INSTANCE_ID