Terraform, How to run the provisioner on existing resources? - openstack

Question

My question is similar to this git hub post:
https://github.com/hashicorp/terraform/issues/745
It is also related to another stack exchange post of mine:
Terraform stalls while trying to get IP addresses of multiple instances?
I am trying to bootstrap several servers and there are several commands I need to run on my instances that require the IP addresses of all the other instances. However I cannot access the variables that hold the IP addresses of my newly created instances until they are created. So when I try to run a provisioner "remote-exec" block like this:
provisioner "remote-exec" {
inline = [
"sudo apt-get update",
"sudo apt-get install -y curl",
"echo ${openstack_compute_instance_v2.consul.0.network.0.fixed_ip_v4}",
"echo ${openstack_compute_instance_v2.consul.1.network.1.fixed_ip_v4}",
"echo ${openstack_compute_instance_v2.consul.2.network.2.fixed_ip_v4}"
]
}
Nothing happens because all the instances are waiting for all the other instances to finish being created and so nothing is created in the first place. So I need a way for my resources to be created and then run my provisioner "remote-exec" block commands after they are created and terraform can access the IP addresses of all my instances.

Answer 1

The solution is to create a resource "null_resource" "nameYouWant" { } and then run your commands inside that. They will run after the initial resources are created:
resource "aws_instance" "consul" {
count = 3
ami = "ami-ce5a9fa3"
instance_type = "t2.micro"
key_name = "ansible_aws"
tags {
Name = "consul"
}
}
resource "null_resource" "configure-consul-ips" {
count = 3
connection {
user = "ubuntu"
private_key="${file("/home/ubuntu/.ssh/id_rsa")}"
agent = true
timeout = "3m"
}
provisioner "remote-exec" {
inline = [
"sudo apt-get update",
"sudo apt-get install -y curl",
"sudo echo '${join("\n", aws_instance.consul.*.private_ip)}' > /home/ubuntu/test.txt"
]
}
}
Also see the answer here:
Terraform stalls while trying to get IP addresses of multiple instances?
Thank you so much #ydaetskcor for the answer

Answer 2

In addition to #alex-cohen answer, another tip from https://github.com/hashicorp/terraform/issues/8266#issuecomment-454377049.
If you want to initiate a call to local-exec, regardless of a resource creation, use triggers:
resource "null_resource" "deployment" {
provisioner "local-exec" {
command = "echo ${PATH} > output.log"
}
triggers = {
always_run = timestamp()
}
}