Assign a spare Elastic IP by tag to a new EKS node

eks_eip_userdata.sh

instance_id=$(curl -s http://169.254.169.254/latest/meta-data/instance-id) 

# Find any unassociated Elastic IPs for this EKS cluster, and associate 1 to this node
allocate_eip () {
  allocation_ids_string=$(aws ec2 describe-addresses --filters Name=tag:cluster,Values=${cluster} --query "Addresses[?NetworkInterfaceId == null ].AllocationId" --output text)
  allocation_ids=($allocation_ids_string)

  # Check if there is at least 1 Elastic IP free
  if [ ${#allocation_ids[@]} -eq 0 ]; then
    return 1
  else
    allocation_id=${allocation_ids[0]}
    echo "Try to associate $allocation_id"
    aws ec2 associate-address --instance-id $instance_id --allocation-id $allocation_id --allow-reassociation}
  fi
}

echo "Checking for free Elastic IPs"
end=$((SECONDS+300))
while [ $SECONDS -lt $end ]; do
    if allocate_eip; then
        echo "Associated Elastic IP $allocation_id"
        exit 0
    else
        echo "Could not associate Elastic IP, waiting 15 seconds..."
        sleep 15
    fi
done

echo "Waited 5 minutes to associate Elastic IP, giving up"
exit 1