Planning Infrastructure Changes

1. Creating Execution Plan

The terraform plan command generates an execution plan that shows what changes Terraform will make to your infrastructure. This is a critical step in the Terraform workflow, allowing you to review changes before applying them.

terraform plan

2. Saving Plan Files

Plan files can be saved to disk using the -out flag. These files can later be applied without re-generating the plan, which is useful for automation and ensuring consistency across environments.

terraform plan -out=production.tfplan

3. Reviewing Plan Output

The plan output provides a detailed view of the changes Terraform will make to your infrastructure. It includes resource creation, modification, and destruction actions.

<span class="highlight">+</span> aws_instance.example
<span class="highlight">~</span> aws_security_group.example
<span class="highlight">-</span> aws_elb.example

4. Using Target Resources

The -target flag allows you to limit the scope of the plan to specific resources. This is useful when working with large configurations and you only want to review changes for a subset of resources.

terraform plan -target=aws_instance.web_server

5. Refreshing State

The -refresh flag controls whether Terraform should refresh the state before generating the plan. By default, it's enabled to ensure the state reflects the current infrastructure.

terraform plan -refresh=false

6. Generating Destroy Plan

To generate a plan for destroying infrastructure, use the -destroy flag. This creates a plan that will remove all resources in the configuration.

terraform plan -destroy

7. Disabling Refresh

The -refresh=false option disables state refresh, which can speed up plan generation but may result in an inaccurate plan if the actual infrastructure has changed since the last refresh.

8. Setting Variable Values

Variables can be set directly on the command line using the -var flag. This is useful for testing different values without modifying configuration files.

terraform plan -var=instance_type=t3.micro -var=environment=prod

9. Using Variable Files

Variable values can be loaded from files using the -var-file flag. This is a common pattern for managing environment-specific configurations.

terraform plan -var-file=prod.tfvars

10. Generating Machine-Readable Output

Terraform can generate machine-readable output in JSON format using the -json flag. This is useful for integrating Terraform into CI/CD pipelines or other automation tools.

terraform plan -json