title: Terraform - list of string required (cidr_blocks in AWS)
body: <p>In Terraform I'm having problems imputing a list that will be stored in a variable. </p>
  
  <p>While executing <code>terraform plan</code>, I get asked for a cidr_blocks (which should be a list of strings).</p>
  
  <p>I tried to type several "forms" that might represent a list of strings but always get an error.
  Examples:</p>
  
  <p>1st attempt:</p>
  
  <pre><code>$terraform plan
  ...
  var.monitoring_access_ips_mysystem
    Enter a value: "10.180.1.0/24", "10.180.2.0/25", "10.180.3.0/23"
  </code></pre>
  
  <p>2nd attempt:</p>
  
  <pre><code>var.monitoring_access_ips_mysystem
    Enter a value: ["10.180.1.0/24", "10.180.2.0/25", "10.180.3.0/23"]
  </code></pre>
  
  <p>3rd attempt:</p>
  
  <pre><code>var.monitoring_access_ips_mysystem
    Enter a value: '["10.180.1.0/24", "10.180.2.0/25", "10.180.3.0/23"]'
  </code></pre>
  
  <p>4th attempt:</p>
  
  <pre><code>var.monitoring_access_ips_mysystem
    Enter a value: "["10.180.1.0/24", "10.180.2.0/25", "10.180.3.0/23"]"
  </code></pre>
  
  <p>5th attempt:</p>
  
  <pre><code>var.monitoring_access_ips_mysystem
    Enter a value: "10.180.1.0/24"
  </code></pre>
  
  <p>For any attempt, the error is always the same:</p>
  
  <pre><code>Error: Incorrect attribute value type
  
    on ecs/security_group.tf line 10, in resource "aws_security_group" "ecs-cluster-sg":
    10:     cidr_blocks = var.monitoring_access_ips_mysystem
  
  Inappropriate value for attribute "cidr_blocks": list of string required.
  </code></pre>
  
  <p>And the <code>ecs/security_group.tf</code> file looks like this
  <strong>ecs/security_group.tf:</strong></p>
  
  <pre><code>resource "aws_security_group" "ecs-cluster-sg" {
    name   = "${var.app_name}-cluster-sg"
    vpc_id = var.vpc_id
  
    ingress {
      description = "Ingress from monitoring VPC on custom port"
      from_port   = 80
      to_port     = 80
      protocol    = "tcp"
      cidr_blocks = var.monitoring_access_ips_mysystem
    }
    ...
  </code></pre>
  
  <p>What valid format can I type/pass the IPs so that it is accepted as a 'list of strings'?</p>