Terraform Associate: Output Data from Terraform

Terraform outputs are a powerful feature that allows you to extract, display, and use information about your deployed infrastructure. Whether you need to retrieve an EC2 instance’s public IP, a database connection string, or a VPC ID to pass between modules, outputs make your infrastructure more transparent and dynamic.

In this guide, we’ll explore:

• How to define output variables.

• Displaying and retrieving outputs.

• Handling multiple values and sensitive outputs.

• Passing outputs between modules.

• Saving outputs for external use.

• Best practices for using outputs.

1. Defining Output Variables

Output variables are defined using the output block in your Terraform configuration. They are useful for capturing and displaying important attributes from your resources.

Example: Output an EC2 Instance’s Public IP

In your Terraform configuration (e.g., outputs.tf), you might define an output variable like this:

output "instance_public_ip" {
  description = "The public IP of the EC2 instance"
  value       = aws_instance.example.public_ip
}

After running your Terraform commands, this output will provide the public IP address of the EC2 instance that was created.

2. Applying Terraform and Viewing Outputs

After applying your Terraform configuration, you can easily view the outputs.

Steps:

1. Apply the Configuration:

    terraform apply
   

2. View All Outputs:

    terraform output
   

   Example output:

    instance_public_ip = "34.216.123.45"
   

3. Retrieve a Specific Output:

    terraform output instance_public_ip
   

   Result:

    34.216.123.45
   

This process allows you to quickly verify key infrastructure details directly from the CLI.

3. Outputting Multiple Values

Terraform makes it easy to output multiple values, whether you’re dealing with a list of items or a map of values.

Example: Output Multiple EC2 Instance IPs

If you have multiple instances, you can output all their public IPs as a list:

output "instance_ips" {
  description = "List of instance public IPs"
  value       = aws_instance.example[*].public_ip
}

Example output:

instance_ips = [
  "34.216.123.45",
  "35.172.85.10"
]

This approach is particularly useful for scaling or when you need to reference multiple resources simultaneously.

4. Marking Outputs as Sensitive

Outputs that contain sensitive information, such as passwords or private keys, should be protected to prevent exposure.

Example: Masking a Sensitive Output

output "db_password" {
  description = "Database password"
  value       = aws_db_instance.example.password
  sensitive   = true
}

When you run:

terraform output

The sensitive value will be masked:

db_password = <sensitive>

Important: Marking an output as sensitive prevents it from being displayed in plain text but does not remove it from the Terraform state file.

5. Using Outputs in Other Terraform Modules

Outputs can be used as inputs for other modules, allowing you to pass values dynamically between different parts of your configuration.

Example: Passing Outputs Between Modules

Module 1 (vpc/main.tf)

output "vpc_id" {
  description = "VPC ID"
  value       = aws_vpc.main.id
}

Module 2 (ec2/main.tf)

module "vpc" {
  source = "../vpc"
}

resource "aws_instance" "example" {
  # Use the VPC ID output from the VPC module
  vpc_security_group_ids = [module.vpc.vpc_id]
}

This modular approach keeps your configurations clean and promotes reuse across environments.

6. Saving Terraform Outputs for External Use

Outputs can be saved and utilized outside of Terraform, which is useful for automation, integration with other tools, or simple record-keeping.

a) Save Outputs to a JSON File

Use the terraform output -json command to export outputs in JSON format:

terraform output -json > terraform_outputs.json

Example JSON output:

{
  "instance_public_ip": {
    "value": "34.216.123.45",
    "type": "string"
  }
}

b) Use Outputs in a Shell Script

Retrieve an output value directly in a shell script for automation:

INSTANCE_IP=$(terraform output -raw instance_public_ip)
echo "Instance IP: $INSTANCE_IP"

This makes it easy to integrate Terraform outputs into your CI/CD pipelines or other automation workflows.

7. Best Practices for Terraform Outputs

• Retrieve Essential Details: Use outputs to capture crucial information like IP addresses, resource IDs, and endpoints.

• Protect Sensitive Data: Mark outputs as sensitive to prevent exposure of sensitive information.

• Promote Reusability: Pass outputs between modules to maintain modular and reusable configurations.

• Automate with JSON: Save outputs in JSON format when integrating with external tools or scripts.

• Keep It Clean: Only output the information that is necessary for downstream processes or user visibility.

Conclusion

Terraform outputs are a versatile tool for extracting and using information about your deployed infrastructure. By defining and managing outputs properly, you can:

• Easily verify resource attributes.

• Pass critical data between modules.

• Secure sensitive information.

• Integrate Terraform with other tools and workflows.

Implementing these practices helps ensure that your infrastructure is not only robust but also transparent and adaptable. Happy Terraforming!

Reference

1. Terraform Outputs Documentation
   Dive into the official Terraform documentation to understand how to define and manage output variables in your configurations.

2. Terraform CLI Output Command
   Explore the usage and options of the terraform output command for retrieving and formatting your infrastructure data.

3. Terraform Modules: Using Outputs
   Learn how to pass outputs between modules to create modular, reusable, and maintainable Terraform configurations.

4. Securing Sensitive Data in Terraform
   Understand best practices for marking outputs as sensitive to protect critical information from exposure.

5. Automating Workflows with Terraform JSON Outputs
   Discover how to export Terraform outputs in JSON format for seamless integration with external tools and CI/CD pipelines.