{"id":2037,"date":"2024-05-31T08:12:00","date_gmt":"2024-05-31T06:12:00","guid":{"rendered":"https:\/\/robermb.com\/blog\/?p=2037"},"modified":"2024-06-01T18:26:10","modified_gmt":"2024-06-01T16:26:10","slug":"terraform-variable-definition-precedence","status":"publish","type":"post","link":"https:\/\/robermb.com\/blog\/geeks\/terraform-variable-definition-precedence\/","title":{"rendered":"Terraform Variable Definition Precedence"},"content":{"rendered":"\n

In Terraform, the order of precedence for variable assignment determines which value is used when multiple sources are available. Here’s the order of precedence from lowest to highest:<\/p>\n\n\n\n

1. Default Values in Variable Definitions<\/strong> (default<\/code>):
If no other value is provided, the default value defined in the variable block is used.<\/p>\n\n\n\n

variable \"region\" {\n  type        = string\n  description = \"The region where resources will be deployed\"\n  default     = \"us-west-1\"\n}<\/code><\/pre>\n\n\n\n
2. Environment Variables<\/strong> (TF_VAR_<\/code>):
Environment variables that follow the format TF_VAR_name<\/code>. For example, for the variable region<\/code>, you can set it in your execution environment as TF_VAR_region<\/code>.<\/p>\n\n\n\n
export TF_VAR_region=\"us-east-1\"<\/code><\/pre>\n\n\n\n
3. terraform.tfvars<\/code> or *.auto.tfvars<\/code> Files<\/strong>:
Terraform automatically looks for files named terraform.tfvars<\/code> or files with the .auto.tfvars<\/code> extension in the current directory and applies the values defined in them.<\/p>\n\n\n\n
# terraform.tfvars\nregion = \"us-east-1\"<\/code><\/pre>\n\n\n\n
4. Specific Variable Files<\/strong>:
You can specify a custom variable file using the -var-file<\/code> flag on the command line.<\/p>\n\n\n\n
terraform apply -var-file=\"custom.tfvars\"<\/code><\/pre>\n\n\n\n
5. Command-Line Flags<\/strong> (-var<\/code>):
You can pass values directly on the command line using the -var<\/code> flag. This method has the highest precedence and will override any other defined values.<\/p>\n\n\n\n
terraform apply -var=\"region=us-east-2\"<\/code><\/pre>\n\n\n\n
Practical Example<\/h2>\n\n\n\n
Suppose you have a Terraform configuration with a variable named region<\/code> defined as follows:<\/p>\n\n\n\n
# variables.tf\nvariable \"region\" {\n  type        = string\n  description = \"The region where resources will be deployed\"\n  default     = \"us-west-1\"\n}<\/code><\/pre>\n\n\n\n
And you have the following files and configurations:<\/p>\n\n\n\n
1. terraform.tfvars<\/code> File<\/strong>:<\/p>\n\n\n\n
region = \"us-east-1\"<\/code><\/pre>\n\n\n\n
2. Custom Variable File custom.tfvars<\/code><\/strong>:<\/p>\n\n\n\n
region = \"us-west-2\"<\/code><\/pre>\n\n\n\n
3. Environment Variable<\/strong>:<\/p>\n\n\n\n
export TF_VAR_region=\"eu-central-1\"<\/code><\/pre>\n\n\n\n
4. Command-Line Flag<\/strong>:<\/p>\n\n\n\n
terraform apply -var=\"region=us-east-2\"<\/code><\/pre>\n\n\n\n
Precedence Order in Action<\/h2>\n\n\n\n
1. If you run terraform apply<\/strong><\/code> without any other options:
The value from the terraform.tfvars<\/code> file (us-east-1<\/strong><\/code>) will be used.<\/p>\n\n\n\n
2. If you run terraform apply -var-file=\"custom.tfvars\"<\/strong><\/code>:
The value from the custom.tfvars<\/code> file (us-west-2<\/strong><\/code>) will be used.<\/p>\n\n\n\n
3. If you have the environment<\/strong> variable<\/strong> TF_VAR_region<\/strong><\/code> set:
The value from the environment variable (eu-central-1<\/strong><\/code>) will be used.<\/p>\n\n\n\n
4. If you use the command-line flag -var<\/code><\/strong>:
The value passed on the command line (us-east-2<\/strong><\/code>) will be used, overriding any other value.<\/p>\n\n\n\n
Summary<\/h2>\n\n\n\n
The order of precedence for variable assignment in Terraform is crucial to understanding which value will be used when multiple sources are available. 

The precedence<\/strong> order<\/strong> from<\/strong> lowest<\/strong> to highest<\/strong> is:<\/p>\n\n\n\n
    \n
  1. Default values in variable definitions.<\/li>\n\n\n\n
  2. Environment variables (TF_VAR_<\/code>).<\/li>\n\n\n\n
  3. terraform.tfvars<\/code> or *.auto.tfvars<\/code> files.<\/li>\n\n\n\n
  4. Specific variable files (-var-file<\/code>).<\/li>\n\n\n\n
  5. Command-line flags (-var<\/code>).<\/li>\n<\/ol>\n\n\n\n
    This order allows you to control and override variable values flexibly according to your needs.<\/p>\n","protected":false},"excerpt":{"rendered":"
    In Terraform, the order of precedence for variable assignment determines which value is used when multiple sources are available. Here’s … More Terraform Variable Definition Precedence<\/span> →<\/span><\/a><\/p>\n","protected":false},"author":1,"featured_media":2031,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[103,2],"tags":[112,126,131],"_links":{"self":[{"href":"https:\/\/robermb.com\/blog\/wp-json\/wp\/v2\/posts\/2037"}],"collection":[{"href":"https:\/\/robermb.com\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/robermb.com\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/robermb.com\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/robermb.com\/blog\/wp-json\/wp\/v2\/comments?post=2037"}],"version-history":[{"count":2,"href":"https:\/\/robermb.com\/blog\/wp-json\/wp\/v2\/posts\/2037\/revisions"}],"predecessor-version":[{"id":2039,"href":"https:\/\/robermb.com\/blog\/wp-json\/wp\/v2\/posts\/2037\/revisions\/2039"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/robermb.com\/blog\/wp-json\/wp\/v2\/media\/2031"}],"wp:attachment":[{"href":"https:\/\/robermb.com\/blog\/wp-json\/wp\/v2\/media?parent=2037"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/robermb.com\/blog\/wp-json\/wp\/v2\/categories?post=2037"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/robermb.com\/blog\/wp-json\/wp\/v2\/tags?post=2037"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}