Terraform Variables

In Coder, Terraform templates offer extensive flexibility through template-wide variables. These variables, managed by template authors, facilitate the construction of customizable templates. Unlike parameters, which are primarily for workspace customization, template variables remain under the control of the template author, ensuring workspace users cannot modify them.

Given that variables are a fundamental concept in Terraform, Coder endeavors to fully support them. Native support includes string, number, and bool formats. However, other types such as list(string) or map(any) will default to being treated as strings.

Default value

Upon adding a template variable, it's mandatory to provide a value during the first push. At this stage, the template administrator faces two choices:

1. No default property: opt not to define a default property. Instead, utilize the --var name=value command-line argument during the push to supply the variable's value.
2. Define default property: set a default property for the template variable. If the administrator doesn't input a value via CLI, Coder automatically uses this default during the push.

After the initial push, variables are stored in the database table, associated with the specific template version. They can be conveniently managed via Template Settings without requiring an extra push.

Resolved values vs. default values

It's crucial to note that Coder templates operate based on resolved values during a push, rather than default values. This ensures that default values do not inadvertently override the configured variable settings during the push process.

This approach caters to users who prefer to avoid accidental overrides of their variable settings with default values during pushes, thereby enhancing control and predictability.

If you encounter a situation where you need to override template settings for variables, you can employ a straightforward solution:

1. Create a terraform.tfvars file in the template directory:

   coder_image = newimage:tag

2. Push the new template revision using Coder CLI:

   coder templates push my-template -y # no need to use --var

This file serves as a mechanism to override the template settings for variables. It can be stored in the repository for easy access and reference. Coder CLI automatically detects it and loads variable values.

Input options

When working with Terraform configurations in Coder, you have several options for providing values to variables using the Coder CLI:

1. Manual input in CLI: You can manually input values for Terraform variables directly in the CLI during the deployment process.
2. Web UI: You can set or edit variable values under Variables in the template's settings.
3. Command-line argument: Utilize the --var name=value command-line argument to specify variable values inline as key-value pairs.
4. Variables file selection: Alternatively, you can use a variables file selected via the --variables-file values.yml command-line argument. This approach is particularly useful when dealing with multiple variables or to avoid manual input of numerous values. Variables files can be versioned for better traceability and management, and it enhances reproducibility.

Here's an example of a YAML-formatted variables file, values.yml:

In this sample file:

• region, bucket_name, zone_types, and cpu are Terraform variable names.
• Corresponding values are provided for each variable.
• The zone_types variable demonstrates how to provide a JSON-formatted string as a value in YAML.

Terraform .tfvars files

In Terraform, .tfvars files provide a convenient means to define variable values for a project in a reusable manner. These files, ending with either .tfvars or .tfvars.json, streamline the process of setting numerous variables.

By utilizing .tfvars files, you can efficiently manage and organize variable values for your Terraform projects. This approach offers several advantages:

• Clarity and consistency: Centralize variable definitions in dedicated files, enhancing clarity, instead of input values on template push.
• Ease of maintenance: Modify variable values in a single location under version control, simplifying maintenance and updates.

Coder automatically loads variable definition files following a specific order, providing flexibility and control over variable configuration. The loading sequence is as follows:

1. terraform.tfvars: This file contains variable values and is loaded first.
2. terraform.tfvars.json: If present, this JSON-formatted file is loaded after terraform.tfvars.
3. \*.auto.tfvars: Files matching this pattern are loaded next, ordered alphabetically.
4. \*.auto.tfvars.json: JSON-formatted files matching this pattern are loaded last.