parametrized terraform template - templates

Question

I have a terraform project to create a 99 virtual machines in Openstack i can not use cloud-init and i must modify the hostname of every machine
hostname.tplt :
sudo sed -i -e "s/debian[7-9]/${host_name}/g" /etc/hostname
sudo invoke-rc.d hostname.sh start
sudo sed -i -e "s/127\.0\.1\.1.*/127.0.1.1\t${host_name}.${domain_name} ${host_name}/g" /etc/hosts
sudo apt-get update && sudo apt-get -y install dbus && sudo hostnamectl set-hostname ${host_name}
part of main.tf :
data "template_file" "hostname_servers" {
template = "${file("templates/hostname.tplt")}"
vars {
host_name = "${format("%s-proxy-%02d", var.prefix_name, count.index+1)}"
domain_name = "${var.domain_name}"
}
}
Ressource
resource "openstack_compute_instance_v2" "proxy-instance" {
count = "${var.count_proxy}"
name = "${format("%s-proxy-%02d", var.prefix_name, count.index+1)}"
image_name = "${var.image}"
flavor_name = "${var.flavor_proxy}"
network {
name = "${format("%s-%s", var.prefix_name, var.network_name)}"
}
connection {
user = "${var.user}"
}
provisioner "remote-exec" {
inline = [
"${data.template_file.hostname_servers.rendered}"
]
}
}
the use case :
when i start a terraform plan it works for the proxy-instance resource but i need to do that for the 99 machines,
i don't like to duplicate the templates data 99 times,
and i don't know how to parammetrize the template to be able to apply for all the machines
any idea ?

Answer 1

If you set count to the same value on multiple resources then you can use count.index to create correspondences between the instances of one block and the instances of another, like this:
data "template_file" "hostname_servers" {
count = "${var.count_proxy}"
template = "${file("templates/hostname.tplt")}"
vars {
host_name = "${format("%s-proxy-%02d", var.prefix_name, count.index+1)}"
domain_name = "${var.domain_name}"
}
}
resource "openstack_compute_instance_v2" "proxy-instance" {
count = "${var.count_proxy}"
name = "${format("%s-proxy-%02d", var.prefix_name, count.index+1)}"
image_name = "${var.image}"
flavor_name = "${var.flavor_proxy}"
network {
name = "${format("%s-%s", var.prefix_name, var.network_name)}"
}
connection {
user = "${var.user}"
}
provisioner "remote-exec" {
inline = [
# use count.index to match the template instance corresponding
# to this compute instance instance.
"${data.template_file.hostname_servers.*.rendered[count.index]}"
]
}
}