[1] main.tf

1. What is a Resource?

• Resources are code blocks that define infrastructure components.
• A resource is declared using the resource keyword, followed by the resource type and a custom resource name.

2. Resource Type and Name

• The resource type depends on the provider (e.g., Google Cloud) defined in your configuration.
• Example:

  resource "google_storage_bucket" "example-bucket" {
    name     = "example-bucket"
    location = "US"
  }

• Resource type (e.g., google_storage_bucket) identifies the cloud resource being provisioned.
• The resource name (e.g., example-bucket) is a custom identifier that distinguishes different resources of the same type within your configuration.
• Terraform uses the resource type and resource name together to uniquely identify each infrastructure component.

3. Resource Arguments

• Within the {} brackets, you define the arguments required for the resource configuration.
• Required arguments vary depending on the resource type:
  • For google_storage_bucket, you need to specify the name and location to create the resource.
  • For google_compute_instance, you must provide name, machine_type, and network_interface.

4. Optional Arguments

• Some arguments, like zone and tags, are optional when defining certain resource types (e.g., google_compute_instance).

5. Organizing Resource Blocks

• If your configurations become lengthy, you can split them into separate files. For example, use different files for instances, storage buckets, and datasets to keep the code organized.

[2] providers.tf

Configuring Providers in Terraform

1. Provider Local Name

• The provider's local name (e.g., google) is used to specify which cloud provider to configure.
• To ensure the correct configuration, the provider must be included in the required_providers block.

2. Provider-Specific Arguments

• Arguments like project and region are specific to the Google provider.

3. Default Provider Configuration

• If a provider block is not included, Terraform assumes a default empty configuration.

4. Provider Versioning

• You can assign a version to each provider.
• Although the version argument is optional, it's recommended to avoid downloading breaking changes with new versions.
• The version argument constrains the provider to a specific version or a range of versions.
• If no version is specified, Terraform will download the most recent provider during initialization.

[3] variables.tf

1. What Are Variables?

• Variables are used to parameterize your configuration, making it flexible and reusable.
• Input variables act as parameters that allow easy customization and sharing without modifying the source code.

2. Setting Variable Values

• Once defined, variable values can be set in various ways at runtime:
  • Environment variables
  • CLI options
  • Key-value files (e.g., .tvars extension)
• This enables you to define resource attributes centrally or at runtime.

3. Parameterizing Attributes

• You can separate attributes from deployment plans for better organization.
• Example: In main.tf, a Cloud Storage bucket is declared, and the location attribute is parameterized.
• The location value is declared as a variable in the variables.tf file, allowing you to define it dynamically during runtime.

[4] output.tf

1. What Are Output Values?

• The outputs.tf file is used to hold output values from your resources.
• Resource instances managed by Terraform export attributes, which can be used elsewhere in the configuration.

2. Purpose of Output Values

• Output values allow you to expose and access important resource attributes.
• Some attributes, like a resource's self-link or a bucket URL, are computed upon creation and may be required for tasks like accessing the resource or uploading objects.

3. Defining Output Values

• The label after the output keyword is the name, which must be a valid identifier.
• In the root module, the output name is displayed to the user.
• In a child module, the output name can be used to access the value.

4. Value Expression

• The value argument takes an expression that returns the result to the user.

[5] terraform.tfstate

• Terraform saves the state of managed resources in a state file.
• By default, the state file is stored locally, but it can also be stored remotely, which is preferred in team environments .
• The state file is automatically created and updated by Terraform, so do not modify it manually.

[6] modules

• A module is a set of Terraform configuration files in a single directory.
• Even a simple configuration with one or more .tf files in a directory is considered a module.
• Modules are the primary method for code reuse in Terraform.
• They can be reused by specifying the source from which the module's code can be retrieved.
• Sources can be either local or remote.

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Reference: https://youtu.be/nnxC2RYhcCI