amazon ec2 - How to iterate over all aws_instances in terraform? -

i'm relatively new terraform , i'm trying iterate on aws_instances apply null_resource. can use multiple splats access instances, regardless of names?

the ec2 instances broken down 3 types:

aws_instance.web.* (3 instances) aws_instance.app.* (3 instances) aws_instance.db.*  (2 instances) 

here's attempt apply null_resource 8 aws_instances:

resource "null_resource" "install_security_package" {    #count = "${length(aws_instance)}" #terraform error: resource count can't reference variable: aws_instance   #count = "${length(aws_instance.*)}" #terraform error: resource variables must 3 parts: type.name.attr   count = "${length(aws_instance.*.*)}" #terraform error: unknown resource 'aws_instance.*'    connection {     type        = "ssh"     host        = "${element(aws_instance.*.private_ip, count.index)}"     user        = "${lookup(var.user, var.platform)}"     private_key = "${file("${var.private_key_path}")}"     timeout     = "2m"   }    provisioner "remote-exec" {     inline = [       "sudo rpm -uvh http://www.example.com/security/repo/security_baseline.rpm",     ]   } } 

it not possible match resources of given type. "splat" syntax, you've seen, allows selecting of instances created particular resource block.

the closest can terraform today concatenate different resources:

concat(aws_instance.web.*.private_ip, aws_instance.app.*.private_ip, aws_instance.db.*.private_ip) 

in current version of terraform of answer necessary use of workarounds shared in github issue #4084 in order avoid duplicating complex expression in multiple places. forthcoming feature called local values make simpler in near future, allowing list given name re-used in multiple places:

# won't work until terraform pr#15449 merged , released locals {   aws_instance_addrs = "${concat(aws_instance.web.*.private_ip, aws_instance.app.*.private_ip, aws_instance.db.*.private_ip)}" }  resource "null_resource" "install_security_package" {    count = "${length(local.aws_instance_addrs)}"    connection {     type        = "ssh"     host        = "${local.aws_instance_addrs[count.index]}"     user        = "${lookup(var.user, var.platform)}"     private_key = "${file("${var.private_key_path}")}"     timeout     = "2m"   }    provisioner "remote-exec" {     inline = [       "sudo rpm -uvh http://www.example.com/security/repo/security_baseline.rpm",     ]   } }