Terraform

# register key
curl -fsSL https://apt.releases.hashicorp.com/gpg | sudo apt-key add -
# add repo
sudo apt-add-repository "deb [arch=$(dpkg --print-architecture)] https://apt.releases.hashicorp.com $(lsb_release -cs) main"
# install with apt
sudo apt install terraform

# create a security group named secgroup_1
resource "openstack_networking_secgroup_v2" "secgroup_1" {
  # you can access the variables using var.<variable-name>
  name        = var.http_sec_group
  description = "My neutron security group"
}

# create a security group rules
resource "openstack_networking_secgroup_rule_v2" "secgroup_rule_1" {
  direction         = "ingress"
  ethertype         = "IPv4"
  protocol          = "tcp"
  port_range_min    = 80
  port_range_max    = 80
  remote_ip_prefix  = "0.0.0.0/0"
  # you can access the output attribute of other resources using ${<provider>.<name>.<attribute>}
  security_group_id = "${openstack_networking_secgroup_v2.secgroup_1.id}"
}

#creating instances
resource "openstack_compute_instance_v2" "Instance" {
  # the count will create a number of duplicates equal to the number
  count = var.instance_num
  name = format("%s-%02d", var.instance_name, count.index+1)
  image_id = var.image_id
  flavor_id = var.flavor_id
  key_pair = var.key_pair_name
  security_groups = var.security_groups
  network {
    name = var.network_name
  }
}

resource "openstack_blockstorage_volume_v2" "Volume" {
  count = var.instance_num
  name        = format("%s-%02d", var.volume_name, count.index+1)
  size        = var.volume_size
}

resource "openstack_compute_volume_attach_v2" "attachments" {
  count       = var.instance_num
  # if there are multiples of same resources the detail are stored in an array 
  instance_id = "${openstack_compute_instance_v2.Instance[count.index].id}"
  volume_id   = "${openstack_blockstorage_volume_v2.Volume[count.index].id}"
}

# this will create a output which you can use
output "instance_ips" {
    value = {
        for instance in openstack_compute_instance_v2.Instance:
         instance.name => instance.access_ip_v4
    }
}

# create a SSH key-pair using other method first since terraform is not secure 
variable "key_pair_name" {
    description = "key pair name"
    default = "tutorial"
}

variable "http_sec_group" {
    description = "custom security group name"
    default = "HTTP-ingress"
}

variable "network_name" {
    description = "The network to be used."
    default  = "Internal"
}

variable "instance_name" {
    description = "The Instance Name to be used."
    default  = "tutorial-machine"
}

variable "image_id" {
    #find with: openstack image list
     description = "The image ID to be used."
    default  = "622cb70d-c88c-4dc4-99e6-df8b8f9965d7"
}

variable "flavor_id" {
    #find with: openstack flavor list
    description = "The flavor id to be used."
    default  = "026ace2c-5247-4bdc-8929-81d129cc69bf"
}

# have to put http sec group here as well
variable "security_groups" {
    description = "List of security group"
    type = list
    default = ["default", "HTTP-ingress"]
}

variable "instance_num" {
    description = "The keypair public key."
    default = 1
}

variable "volume_name" {
    description = "name of volume"
    default = "tutorial_volume"
}

variable "volume_size" {
    description = "size of volume"
    default = 3
}

$ terraform plan -var "instance_num=2"

# Terraform will compare the configuration witht the desired state and produce a action plan

$ terraform apply -var "instance_num=2"

##################################################
Same as above Skipped
###################################################
Apply complete! Resources: 8 added, 0 changed, 0 destroyed.

Outputs:

instance_ips = {
  "tutorial-machine-01" = "172.16.100.135"
  "tutorial-machine-02" = "172.16.101.124"
}