Terraform plan vs. terraform apply
Terraform, developed by HashiCorp, is an open-source infrastructure as code (IaC) tool. It empowers users to articulate and deploy infrastructure using code to facilitate the automation of the complete infrastructure lifecycle and encompass the creation, modification, and removal of resources. Terraform supports various cloud providers, on-premises data centers, and other infrastructure components, making it a versatile solution for managing infrastructure in a consistent and scalable manner.
In this Answer, we will discuss two important Terraform commands: terraform plan and terraform apply.
The terraform plan command
The terraform plan command analyzes the desired state described in the Terraform configuration files and generates an execution plan. It calculates the changes required to achieve the desired state and provides an overview of the infrastructure modifications that Terraform will apply.
Workflow
During the planning phase, Terraform examines the current state of the infrastructure and compares it to the proposed changes specified in the Terraform configuration files. It identifies any additions, modifications, or deletions required to reach the desired state and generates a report.
Syntax
terraform plan
Running the terraform plan command allows users to review the impact of their proposed changes before applying them, ensuring they are aware of potential modifications and their consequences.
Here is the output the dummy output for the terraform plan command:
The terraform apply command
The terraform apply command executes the changes specified in the Terraform configuration files. It provisions or modifies the defined infrastructure resources, creating or updating the real-world infrastructure based on the desired state described in the configuration.
Workflow
Once the user reviews the execution plan generated by the terraform plan command and is satisfied with the proposed changes, they can proceed with the terraform apply command to initiate the provisioning process. Terraform applies modifications to the infrastructure, creating new resources, updating existing ones, or deleting obsolete resources.
Syntax
terraform apply
Running the terraform apply command allows users to apply the planned changes to their infrastructure, ensuring that the desired state is implemented.
Here is the dummy output after running terraform apply command:
Code
Let’s take a look at a simple example that distinguishes between the terraform plan and terraform apply commands. We begin by utilizing the terraform plan command, which calculates the necessary changes. After executing this command, we can observe the absence of any added files in the module when using the ls command.
However, when we proceed with the terraform apply command, we can observe that the file specified in main.tf is added to the module, as confirmed by the ls command.
Note: The Terraform version used in this Answer is Terraform v1.4.6.
resource "local_file" "creating_file" {
content = "Content will be written after using terraform apply"
filename = "${path.module}/planVsApply.txt"
}Sum up
The terraform plan command provides an execution plan to allow users to review the proposed changes and understand their impact without actually modifying the infrastructure. On the other hand, the terraform apply command applies the changes to the infrastructure, provisioning or modifying resources based on the desired state defined in the Terraform configuration. Understanding the differences between these commands helps users ensure the accuracy and predictability of infrastructure changes while working with Terraform.
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