Terraform Concepts

Internal

• Terraform

Overview

Terraform is a tool for building, changing and managing infrastructure, as code. It uses a configuration language named Hashicorp Configuration Language (HCL). Terraform is platform agnostic, and achieves that by using different provider APIs for resource provisioning, via plug-ins. A heterogenous environment can be managed with the same workflow.

Hashicorp Configuration Language (HCL)

HCL is human-readable. Configuration can also be JSON, but JSON is only recommended when the configuration is generated by a machine. Internally, the declarative language that drives provider API for resource provisioning.

Provider

https://www.terraform.io/docs/providers/index.html

A provider is responsible for creating and managing resources. Terraform uses provider plug-ins to translate its configuration into API instructions for the provider. In a configuration file, a provider is specified in a "provider" block. Multiple provider blocks can exist in a Terraform configuration file.

Configured in the “provider” block.

Provider Plug-In

Provider-specific resources are managed with provider plugins. Each provider plugin is a an encapsulated binary, distributed separated by Terraform. They are downloaded by terraform init and stored in a subdirectory of the current working directory.

Available Providers

AWS

AWS

Kubernetes

https://www.terraform.io/docs/providers/kubernetes/index.html

Helm

https://www.terraform.io/docs/providers/helm/index.html

Provisioning

In this context, provisioning means initialization of the resources created by the “apply” step by performing software provisioning. Another name for provisioning is instance initialization.

Provisioner

https://www.terraform.io/docs/provisioners/index.html

A provisioner uploads files, runs shell scripts, installs and trigger other software like configuration management tools. A provisioner is only run when the resource is created. The provisioner is declared inside a resource block with the “provisioner” keyword.

resource "aws_instance" "example" {
  … 
  provisioner "local-exec" {
    command = "echo ${aws_instance.example.public_ip} > ip_address.txt"
  }
}

Multiple provisioner blocks can be added.

Failed Provisioner

https://learn.hashicorp.com/terraform/getting-started/provision#failed-provisioners-and-tainted-resources

If a resource is successfully created but fails during provisioning, it is marked as “tainted”.

Available Provisioners

• local-exec
• remote-exec (via ssh, specified with a “connection” keyword) https://learn.hashicorp.com/terraform/getting-started/provision#defining-a-provisioner