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Terraform

Terraform Module Input: Passing Multiple Provider Aliases

By Filip on 11/20/2024

Learn how to efficiently manage and organize your Terraform code by passing multiple provider aliases to a single module for greater flexibility and reusability.

Terraform Module Input: Passing Multiple Provider Aliases

Table of Contents

Introduction

When working with Terraform modules, you might need to utilize different instances of the same provider, each configured with unique settings. This is where provider aliases come in handy. This guide demonstrates how to use multiple provider aliases within your Terraform modules.

Step-by-Step Guide

To use multiple provider aliases within a Terraform module, follow these steps:

1. Define Provider Aliases:

provider "aws" {
  region = "us-west-2"
  alias  = "west"
}

provider "aws" {
  region = "us-east-1"
  alias  = "east"
}

2. Pass Aliases to the Module:

module "my_module" {
  source = "./my_module"

  providers = {
    aws.west = aws.west
    aws.east = aws.east
  }
}

3. Access Aliases within the Module:

resource "aws_instance" "example" {
  provider = aws.west 
  # ... other configurations
}

resource "aws_s3_bucket" "example" {
  provider = aws.east
  # ... other configurations
}

Explanation:

  • Step 1 sets up two AWS providers with aliases "west" and "east".
  • Step 2 passes these aliases to the my_module using the providers meta-argument. Note that the keys (e.g., aws.west) inside the providers block within the module call must match the provider names used within the module.
  • Step 3 demonstrates how resources within the module can utilize these aliases by referencing them via the provider argument.

This approach ensures that resources within your module can leverage different provider configurations based on your requirements.

Code Example

The Terraform code defines two AWS providers with aliases "west" and "east" for regions us-west-2 and us-east-1 respectively. A module "my_module" is called with both provider aliases passed as arguments. Inside the module, an EC2 instance is created in us-west-2 using the "west" provider alias and an S3 bucket is created in us-east-1 using the "east" provider alias. This demonstrates using multiple provider aliases within a module to manage resources in different AWS regions.

main.tf:

terraform {
  required_providers {
    aws = {
      source  = "hashicorp/aws"
      version = "~> 4.0"
    }
  }
}

# Configure AWS providers with aliases
provider "aws" {
  region = "us-west-2"
  alias  = "west"
}

provider "aws" {
  region = "us-east-1"
  alias  = "east"
}

# Use the module and pass provider aliases
module "my_module" {
  source = "./my_module"

  providers = {
    aws.west = aws.west
    aws.east = aws.east
  }
}

my_module/variables.tf:

# No variables needed in this example

my_module/main.tf:

# Create an EC2 instance in us-west-2
resource "aws_instance" "example" {
  provider = aws.west
  ami           = "ami-0c55b159c2d5wi34e" # Replace with your desired AMI
  instance_type = "t2.micro"
  tags = {
    Name = "Example EC2 Instance (West)"
  }
}

# Create an S3 bucket in us-east-1
resource "aws_s3_bucket" "example" {
  provider = aws.east
  bucket = "my-tf-test-bucket-east"
  acl    = "private"

  tags = {
    Name = "Example S3 Bucket (East)"
  }
}

Explanation:

  • main.tf: This file defines two AWS providers with aliases "west" and "east" for different regions. It then calls the my_module and passes these aliases using the providers meta-argument.
  • my_module/main.tf: This file defines two resources:
    • aws_instance.example: This resource uses the aws.west provider alias to create an EC2 instance in the us-west-2 region.
    • aws_s3_bucket.example: This resource uses the aws.east provider alias to create an S3 bucket in the us-east-1 region.

This example demonstrates how to use multiple provider aliases within a Terraform module to manage resources in different AWS regions. You can adapt this approach to use different providers or configurations based on your specific needs.

Additional Notes

  • Provider Namespacing: Using aliases with the format provider_type.alias (e.g., aws.west) is crucial for clarity and avoiding conflicts, especially in larger projects.
  • Module Reusability: This approach makes modules more reusable since they don't rely on specific provider configurations in the root module.
  • Alternative to Multiple Provider Instances: While this example uses separate provider blocks for each alias, you can achieve the same using a single provider block with multiple alias configurations and conditional logic based on variables.
  • Implicit Provider Inheritance: If a module doesn't explicitly declare a provider using the provider argument, it inherits the default provider of the same type from its parent module.
  • Terraform Version Compatibility: Ensure your Terraform version supports provider aliases within modules.
  • State File Considerations: Each provider alias creates a separate namespace within the Terraform state, impacting resource addressing and potential conflicts.
  • Best Practices:
    • Use descriptive alias names that reflect their purpose or environment.
    • Document provider alias usage within your module for better maintainability.
    • Consider using tools like terraform fmt and terraform validate to ensure code style and consistency.
  • Security Considerations: Be mindful of how you manage sensitive information like AWS credentials when using multiple provider aliases, especially in shared environments.

Summary

This article explains how to use different provider configurations within a single Terraform module using provider aliases.

Here's a breakdown:

  1. Define Provider Aliases: Create multiple instances of a provider (e.g., aws) with different configurations (e.g., different regions) and assign each a unique alias.
  2. Pass Aliases to the Module: When calling the module, pass the defined aliases using the providers meta-argument. Ensure the keys in the module call match the provider names used within the module.
  3. Access Aliases within the Module: Inside the module, reference the passed aliases via the provider argument when defining resources to utilize the specific provider configuration.

This method allows for greater flexibility and control over resource deployment by enabling the use of different provider settings within a single module.

Conclusion

By following these steps, you can leverage the power of provider aliases to create more flexible, reusable, and maintainable Terraform modules. This approach is particularly beneficial when dealing with complex deployments that involve multiple regions, environments, or even different cloud providers. Remember to follow best practices for naming, documentation, and security to ensure smooth operations and avoid potential issues.

References

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