Note_Tech

All technological notes.

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Terraform - Language: Resource

Resources
- describes one or more infrastructure objects, such as virtual networks, compute instances, or higher-level components such as DNS records.
Resource Behavior
- explains in more detail how Terraform handles resource declarations when applying a configuration.
Meta-Arguments section
- used to document special arguments that can be used with every resource type, including depends_on, count, for_each, provider, and lifecycle.
Provisioners
- used to document configuring post-creation actions for a resource using the provisioner and connection blocks.
- Since provisioners are non-declarative and potentially unpredictable, we strongly recommend that you treat them as a last resort.

Resource Syntax
resource block
- declares a resource of a specific type with a specific local name.
- Terraform uses the name when referring to the resource in the same module, but it has no meaning outside that module’s scope.
The resource type and name must be unique within a module because they serve as an identifier for a given resource.
Resource names must
- start with a letter or underscore
- may contain only letters, digits, underscores, and dashes.
Example:

# declear an ec2 instance

resource "aws_instance" "web" {
  ami = "ami-a1b2c3d4"
  instance_type = "t2.micro"
}

Within the block body (between { and }) are the configuration arguments for the resource itself.
- The arguments often depend on the resource type. In this example, both ami and instance_type are special arguments for the aws_instance resource type.

Each resource is associated with a single resource type, which determines the kind of infrastructure object it manages and what arguments and other attributes the resource supports.

Providers
- a plugin for Terraform that offers a collection of resource types.
Each resource type is implemented by a provider.
A provider provides resources to manage a single cloud or on-premises infrastructure platform.
Providers are distributed separately from Terraform, but Terraform can automatically install most providers when initializing a working directory.
To manage resources, a Terraform module must specify the required providers.
Most providers need some configuration to access their remote API, which is provided by the root module.
Based on a resource type’s name, Terraform can usually determine which provider to use.
- By convention, resource type names start with their provider’s preferred local name.
- When using multiple configurations of a provider or non-preferred local provider names, you must use the provider meta-argument to manually choose a provider configuration.

Most of the arguments within the body of a resource block are specific to the selected resource type.
- The resource type’s documentation lists which arguments are available and how their values should be formatted.
- The values for resource arguments can make full use of expressions and other dynamic Terraform language features.
Meta-arguments are defined by Terraform and apply across all resource types.

Every Terraform provider has its own documentation, describing its resource types and their arguments.
Some provider documentation is still part of Terraform’s core documentation, but the Terraform Registry is the main home for all publicly available provider docs.

To remove a resource from Terraform, simply delete the resource block from your Terraform configuration.
- By default, after you remove the resource block, Terraform will plan to destroy any real infrastructure object managed by that resource.
Sometimes you may wish to remove a resource from your Terraform configuration without destroying the real infrastructure object it manages. In this case, the resource will be removed from the Terraform state, but the real infrastructure object will not be destroyed.
To declare that a resource was removed from Terraform configuration but that its managed object should not be destroyed, remove the resource block from your configuration and replace it with a removed block:

removed {
  from = aws_instance.example

  lifecycle {
    destroy = false
  }
}