marco@galago:~/Projects/benchmarking⟫ juju deploy cassandra --constraints="arch=amd64 cpu-cores=2 mem=4096 cpu-power=40" -n 3                                                                                                                                                     
Added charm "cs:trusty/cassandra-3" to the environment.
marco@galago:~/Projects/benchmarking⟫ juju status --format=yaml cassandra                                                                                                                                                                                                         
environment: aws-west-2
machines:
  "28":
    agent-state-info: 'cannot run instances: The specified instance type can only
      be used in a VPC. A subnet ID or network interface ID is required to carry out
      the request. (VPCResourceNotSpecified)'
    instance-id: pending
    series: trusty
  "29":
    agent-state-info: 'cannot run instances: The specified instance type can only
      be used in a VPC. A subnet ID or network interface ID is required to carry out
      the request. (VPCResourceNotSpecified)'
    instance-id: pending
    series: trusty
  "30":
    agent-state-info: 'cannot run instances: The specified instance type can only
      be used in a VPC. A subnet ID or network interface ID is required to carry out
      the request. (VPCResourceNotSpecified)'
    instance-id: pending
    series: trusty