Import blocks in Terraform configuration provide a declarative way to bring existing infrastructure resources under Terraform management. Introduced in Terraform 1.5, this feature allows you to define imports within your configuration files rather than relying solely on the command-line import comm…Import blocks in Terraform configuration provide a declarative way to bring existing infrastructure resources under Terraform management. Introduced in Terraform 1.5, this feature allows you to define imports within your configuration files rather than relying solely on the command-line import command.
The import block syntax includes two primary arguments: the 'id' which represents the resource identifier in your cloud provider, and the 'to' argument which specifies the Terraform resource address where the imported resource will be managed.
Example syntax:
import {
id = "i-abcd1234"
to = aws_instance.example
}
When you run 'terraform plan' with import blocks present, Terraform will generate a plan that shows the resource being imported. Running 'terraform apply' completes the import process and updates the state file accordingly.
Key benefits of using import blocks include:
1. **Version Control**: Import configurations can be committed to source control, providing documentation of what was imported and when.
2. **Batch Operations**: Multiple import blocks can be defined in a single file, enabling bulk imports during migrations.
3. **Configuration Generation**: Using the '-generate-config-out' flag with terraform plan creates configuration code for imported resources, reducing manual effort.
4. **Reproducibility**: Team members can review and understand the import process through code review workflows.
Important considerations when using import blocks:
- You must have a corresponding resource block in your configuration for each import
- After successful import, you can remove the import block from your configuration
- The import block does not create resources; it associates existing resources with Terraform state
- Resource IDs vary by provider and resource type
Import blocks represent a significant improvement in Terraform's infrastructure adoption workflow, making it easier to transition manually created or legacy resources into infrastructure-as-code management while maintaining proper documentation and collaboration practices.
Import Blocks in Configuration
Why Import Blocks Are Important
Import blocks represent a significant advancement in Terraform's infrastructure management capabilities. They allow you to bring existing infrastructure resources under Terraform management in a declarative, reviewable, and repeatable way. This is crucial when organizations have resources created manually or through other tools that need to be managed alongside Terraform-provisioned infrastructure.
What Are Import Blocks?
Import blocks are configuration constructs introduced in Terraform 1.5 that allow you to define resource imports within your Terraform configuration files. Unlike the traditional terraform import command, import blocks are written in HCL and stored in your configuration, making the import process part of your infrastructure-as-code workflow.
The basic syntax of an import block is:
import { to = resource_type.resource_name id = "existing-resource-id"}
How Import Blocks Work
1. Declaration: You add an import block to any .tf file in your configuration directory, specifying the target resource address and the ID of the existing resource in your cloud provider.
2. Configuration Generation: When you run terraform plan -generate-config-out=generated.tf, Terraform can automatically generate the corresponding resource configuration based on the imported resource's current state.
3. Planning: During terraform plan, Terraform reads the import block and shows you what will be imported and any configuration drift.
4. Applying: When you run terraform apply, Terraform imports the resource into the state file and associates it with the corresponding resource block.
5. Cleanup: After successful import, you can remove the import block from your configuration as it has served its purpose.
Key Components of Import Blocks
- to: The resource address where the imported resource will be tracked (required) - id: The provider-specific identifier of the existing resource (required) - provider: Optional specification of which provider configuration to use
Benefits Over terraform import Command
- Import operations are visible in version control - Can be reviewed in pull requests before execution - Multiple imports can be batched in a single plan/apply - Supports automatic configuration generation - More predictable and auditable workflow
Exam Tips: Answering Questions on Import Blocks
1. Remember the Terraform Version: Import blocks were introduced in Terraform 1.5. Questions may test your knowledge of which version supports this feature.
2. Understand the Two Required Arguments: The to and id arguments are mandatory. The to specifies the resource address, and id is the cloud provider's resource identifier.
3. Know the Configuration Generation Flag: The flag -generate-config-out with terraform plan creates resource configurations for imported resources. This is frequently tested.
4. Distinguish from terraform import Command: Import blocks are declarative and stored in configuration files, while terraform import is an imperative CLI command. Questions often compare these approaches.
5. State Management: Import blocks add resources to state during terraform apply, not during plan. The resource must have a corresponding resource block in configuration.
6. Post-Import Actions: Remember that import blocks can be removed after successful import since they are only needed for the initial import operation.
7. Provider Argument: When working with multiple provider configurations, the optional provider argument specifies which provider handles the import.
8. Watch for Trick Questions: Some questions may suggest that import blocks modify the actual cloud resource - they do not. They only affect Terraform state and configuration.