Dynamic Provider Configurations in OpenTofu

Managing infrastructure across multiple regions, accounts, or environments is a common challenge. OpenTofu, a powerful open-source Infrastructure as Code (IaC) tool, offers a robust solution for this: dynamic provider configurations. This feature allows you to programmatically define and manage multiple instances of a provider, streamlining your configurations and enhancing scalability.

At its core, this capability revolves around the for_each meta-argument within provider blocks. Let's dive into how it works.

The Power Duo: for_each and alias

To create multiple provider configurations from a single block—say, for different AWS regions—you'll use for_each in conjunction with the alias meta-argument. The for_each iterates over a map or set of strings, and alias gives a common name segment to these dynamically generated provider instances. The alias is mandatory because OpenTofu needs to distinguish these from a single default provider configuration.

Consider this example for configuring the AWS provider for multiple regions:

variable "aws_region_configs" {
  description = "Map of AWS region configurations."
  type = map(object({
    region_name = string
    profile     = optional(string)
  }))
  default = {
    "primary_us_east_1"   = { region_name = "us-east-1", profile = "default_profile" }
    "secondary_eu_west_1" = { region_name = "eu-west-1", profile = "secondary_profile" }
  }
}

provider "aws" {
  for_each = var.aws_region_configs
  alias    = "regional" // All instances will be part of the 'regional' alias

  region  = each.value.region_name
  profile = each.value.profile
}

This creates two AWS provider instances: aws.regional["primary_us_east_1"] and aws.regional["secondary_eu_west_1"].

Using Your Dynamic Providers

Once defined, these aliased provider instances aren't used automatically. You must explicitly tell OpenTofu which resources or modules should use them.

For Resources and Data Blocks: Use the provider meta-argument:

resource "aws_vpc" "per_region_vpc" {
  for_each = var.aws_region_configs // Iterate over the same region map
  provider = aws.regional[each.key] // Explicitly select the dynamic provider

  cidr_block = "10.0.0.0/16" // Typically parameterized
  tags = {
    Name = "vpc-${each.key}"
  }
}

For Modules: Use the providers meta-argument in the module call:

module "regional_network_stack" {
  for_each = var.aws_region_configs
  source   = "./modules/network-stack"

  providers = {
    aws = aws.regional[each.key] // Pass the specific regional provider to the module
  }

  // Other module inputs
  vpc_name_prefix = "module-vpc-${each.key}"
}

The child module (./modules/network-stack/) would then simply define its resources to use the aws provider, which OpenTofu resolves to the instance passed by the parent.

Scaling and Management Considerations

Dynamic provider configurations significantly reduce code duplication (DRY) and make your IaC more maintainable and scalable. As you manage more environments, regions, or cloud accounts, this programmatic approach becomes invaluable.

However, as the number of provider configurations and the complexity of inter-dependencies (especially with module lifecycles) grow, ensuring consistency, managing state, and orchestrating changes across all these dynamic instances can become a significant operational task. This is where a robust infrastructure automation and collaboration platform can provide substantial benefits, offering a higher-level management plane to visualize, govern, and coordinate these dynamic OpenTofu configurations, particularly in team-based or enterprise environments. Platforms like Scalr, for example, are designed to address these kinds of complexities, helping to manage workspaces, variables, and permissions across numerous configurations.

Quick Reference: Dynamic Provider Concepts

Feature	Description	Example Syntax (Referencing)
Definition	Uses for_each and alias in a provider block.	provider "aws" { for_each = ... alias = "name" ... }
each.key	The key from the for_each map/set, used to identify the instance.	aws.name[each.key]
each.value	The value from the for_each map/set, providing data for the instance.	region = each.value.region_code
Resource Usage	Explicitly referenced via the provider meta-argument.	provider = aws.name[each.key]
Module Usage	Passed to child modules via the providers meta-argument.	providers = { aws = aws.name[each.key] }