Variables

We can start to use variables to make our configuration more dynamic.

File cloudcasts.tf:

 1variable infra_env {
 2    type = string
 3    description = "infrastructure environment"
 4}
 5 
 6variable default_region {
 7    type = string
 8    description = "the region this infrastructure is in"
 9    default = "us-east-2"
10}
11 
12variable instance_size {
13    type = string
14    description = "ec2 web server size"
15    default = "t3.small"
16}

Two of these variables have a default value, and we can let Terraform use the defaults. The third infra_env needs defining.

We can pass it in via cli:

1terraform plan -var 'infra_env=staging'

We can create a *.tfvars file:

1# file variables.tfvars
2infra_env="staging"

Then we can run terraform plan -var-file variables.tfvars.

We can create a file ending in *.auto.tfvars, it will be pulled in automatically:

1# file variables.auto.tfvars
2infra_env="staging"

Then we don't need any extra flags when running terraform commands, such as terraform plan!

Updating Resources

And of course, we should use those variables in our defined resources:

 1  
 2 # File cloudcasts.tf
 3  
 4 resource "aws_instance" "cloudcasts_web" {
 5   ami           = data.aws_ami.app.id
 6-  instance_type = "t3.small" 
 7+  instance_type = var.instance_size 
 8  
 9   root_block_device {
10     volume_size = 8 # GB
11     volume_type = "gp3"
12   }
13  
14   tags = {
15-    Name        = "cloudcasts-staging-web" 
16+    Name        = "cloudcasts-${var.infra_env}-web" 
17     Project     = "cloudcasts.io"
18-    Environment = "staging" 
19+    Environment = var.infra_env 
20     ManagedBy   = "terraform"
21   }
22 }
23  
24 resource "aws_eip" "cloudcasts_addr" {
25   vpc      = true
26  
27   tags = {
28-    Name        = "cloudcasts-staging-web-address" 
29+    Name        = "cloudcasts-${var.infra_env}-web-address" 
30     Project     = "cloudcasts.io"
31-    Environment = "staging" 
32+    Environment = var.infra_env 
33     ManagedBy   = "terraform"
34   }
35 }
36  
37 resource "aws_eip_association" "eip_assoc" {
38   instance_id   = aws_instance.cloudcasts_web.id
39   allocation_id = aws_eip.cloudcasts_addr.id
40 }

Run it:

1terraform plan -var-file variables.tfvars
2terraform apply -var-file variables.tfvars