terraform/website/source/docs/configuration/override.html.md

layout	page_title	sidebar_current	description
docs	Overrides	docs-config-override	Terraform loads all configuration files within a directory and appends them together. Terraform also has a concept of overrides, a way to create files that are loaded last and merged into your configuration, rather than appended.

Overrides

Terraform loads all configuration files within a directory and appends them together. Terraform also has a concept of overrides, a way to create files that are loaded last and merged into your configuration, rather than appended.

Overrides have a few use cases:

• Machines (tools) can create overrides to modify Terraform behavior without having to edit the Terraform configuration tailored to human readability.

• Temporary modifications can be made to Terraform configurations without having to modify the configuration itself.

Overrides names must be override or end in _override, excluding the extension. Examples of valid override files are override.tf, override.tf.json, temp_override.tf.

Override files are loaded last in alphabetical order.

Override files can be in Terraform syntax or JSON, just like non-override Terraform configurations.

Example

If you have a Terraform configuration example.tf with the contents:

resource "aws_instance" "web" {
    ami = "ami-408c7f28"
}

And you created a file override.tf with the contents:

resource "aws_instance" "web" {
    ami = "foo"
}

Then the AMI for the one resource will be replaced with "foo". Note that the override syntax can be Terraform syntax or JSON. You can mix and match syntaxes without issue.