# 9. Terraform Variables

### Input Variables

We can define input variables in the config file as follows

```hcl
variable "subnet_prefix" {
  description = "cidr block for the subnet"
  default = "10.0.2.0/24"
  type = string
}
```

* Accessed as `var.<name>`
* `default` value like name suggests is the default value when we don't assign any value to it
* `type = any` means any data type is accepted
  * We can also use lists type or list of objects

#### Usage

Order of precedence // lowest -> highest

1. If we dont specify any value, it will ask us for input while running `terraform apply`.
2. Second is the default value in declaration block
3. `TF_VAR_<name>` environment variable
4. Best way is to use a seperate file for variables with name `terraform.tfvars`
   * We can assign values in that file like
   * ```hcl
     subnet_prefix = "10.0.1.0/24"
     avail_zone = "eu-west-1"
     ```
   * If you want to use other file like `example.tfvars`, you have to specify it while applying config like `terraform apply -var-file example.tfvars`
5. `*.auto.tfvars` file
6. Command line arguments to enter the value of the variables like `terraform apply -var "subnet_prefix=10.0.1.0/24"` or `-var-file`

***

### Local Variables

We can define local variables in the config file as follows

```hcl
locals {
  service_name = "My Service"
  owner = "NomanAziz"
}
```

* Can be accessed as `local.<name>`
* Temporary variables within the scope of the function

***

### [Output Variables](https://notes.nomanaziz.me/devops/infrastructure-as-a-code-iac/terraform/7.-terraform-output)

***

### Types

#### Primitive Types

1. string
2. number
3. bool

#### Complex Types

1. `list(<TYPE>)`
2. `set(<TYPE>)`
3. `map(<TYPE>)`
4. `object({ <ATTR NAME> = <TYPE>, ... })`
5. `tuple([<TYPE>, ...])`

***

### Sensitive Data

#### Mark variables as sensitive

```tf
sensitive=true
```

#### Pass to terraform apply with

* `TV_VAR_variable`
* `-var` (retrieved from secret manager at runtime)

#### Can also use external secret store

* AWS Secrets manager

***


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