Playing with Terraform graph

Let's play around with our VPC a bit to better understand how resource dependencies are handled. Instead of adding a subnet, let's destroy complete infrastructure we have so far and then plan creation from scratch:

$> terraform destroy
$> terraform plan
      # ... 
+ aws_subnet.public
    availability_zone:       "<computed>"
    cidr_block:              "10.0.1.0/24"    map_public_ip_on_launch: "false"
    vpc_id:                  "${aws_vpc.my_vpc.id}"
# ...

Terraform doesn't know the VPC ID yet, so it doesn't show it to you in the plan. Let's apply the template and observe the order of resource creation:

$> terraform apply
aws_vpc.my_vpc: Creating...
  cidr_block:                "" => "10.0.0.0/16"
  default_network_acl_id:    "" => "<computed>"
  default_security_group_id: "" => "<computed>"
  dhcp_options_id:           "" => "<computed>"
  enable_classiclink:        "" => "<computed>"
  enable_dns_hostnames...