Concatenate a String with a Variable in Terraform

TLDR

In Terraform, you can concatenate strings with variables using interpolation syntax (${}) or the join function for more complex cases.

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Concatenating Strings with Variables in Terraform

String concatenation is a common requirement in Terraform configurations, such as dynamically constructing resource names or paths.

Using Interpolation Syntax

The simplest way to concatenate a string with a variable is by using interpolation syntax:

variable "environment" {
  default = "production"
}

output "bucket_name" {
  value = "my-app-${var.environment}-bucket"
}

In this example, the bucket_name output will be "my-app-production-bucket" if the environment variable is set to "production".

Using the join Function

For more complex concatenations, you can use the join function:

variable "tags" {
  default = ["app", "web", "prod"]
}

output "tag_string" {
  value = join("-", var.tags)
}

This will produce a single string: "app-web-prod".

Combining Interpolation and Functions

You can combine interpolation and functions for advanced use cases:

variable "region" {
  default = "us-east-1"
}

output "resource_id" {
  value = "resource-${join("-", [var.region, "123"])}"
}

The resource_id output will be "resource-us-east-1-123".

Best Practices

• Use Meaningful Names: Ensure variable names clearly indicate their purpose.
• Avoid Hardcoding: Use variables for dynamic values instead of hardcoding strings.
• Test Outputs: Use terraform console to verify concatenated strings before applying changes.

By mastering string concatenation, you can create more dynamic and reusable Terraform configurations.