Use array constants instead of scalar values to model complex configurations effectively; they provide structure, reusability, consistency, and better tooling support, enabling cleaner management of role-based access control and multi-environment deployments through structured data patterns.

When working with configuration systems—especially in infrastructure-as-code, data pipelines, or application settings—many developers default to scalar values: strings, numbers, booleans. While simple, these primitives quickly become limiting when modeling real-world complexity. A more powerful approach is to leverage array constants to represent structured, repeatable, and composable configuration patterns.

Why Move Beyond Scalars?

Scalar values work fine for basic settings like timeout = 30 or enabled = true. But real configurations often involve lists of resources, sets of rules, or multi-environment deployments. Trying to encode these as strings (e.g., comma-separated lists) or individual flags leads to:

• Brittle parsing logic
• Poor readability
• Hard-to-maintain duplication
• Limited type safety

By using array constants, you gain:

• Structure: Each item can be a complex object
• Reusability: Define once, reference in multiple places
• Consistency: Enforce uniform schema across environments
• Tooling support: IDE autocomplete, validation, diffing

Using Array Constants for Role-Based Access Control

Consider defining IAM roles across environments. Instead of hardcoding permissions per service, define a reusable array constant:

# roles.tf
locals {
  s3_permissions = [
    "s3:GetObject",
    "s3:ListBucket",
    "s3:GetObjectVersion"
  ]

  lambda_policy = {
    actions   = local.s3_permissions
    resource  = "arn:aws:s3:::app-data-*"
    effect    = "Allow"
  }

  ec2_policy = {
    actions   = ["ec2:Describe*"]
    resource  = "*"
    effect    = "Allow"
  }

  common_policies = [
    local.lambda_policy,
    local.ec2_policy
  ]
}

Now common_policies is a reusable array of policy objects. It can be referenced in multiple IAM roles or modules, reducing duplication and ensuring consistency.

This pattern shines when combined with for_each or dynamic blocks in Terraform, or when passed into functions in other config languages (like CUE, Jsonnet, or even TypeScript-based CDK).

Managing Multi-Environment Deployments

Array constants also simplify environment-specific configurations. Define variations once, then select based on context:

locals {
  regions = {
    staging = ["us-east-1"]
    production = [
      "us-east-1",
      "us-west-2",
      "eu-west-1"
    ]
  }

  instance_types = {
    dev       = ["t3.micro"]
    staging   = ["t3.small"]
    prod      = ["m5.large", "m5.xlarge"]
  }
}

Now your deployment logic can pull the correct array based on environment:

resource "aws_instance" "app" {
  for_each = toset(local.instance_types[var.environment])

  instance_type = each.key
  # ... other config
}

This keeps configuration DRY and makes intent clear: staging uses small instances, prod uses larger, scalable types.

Best Practices for Array Constants

To get the most out of array-based configurations:

• Name meaningfully: Use allowed_origins, not list1
• Group by domain: Keep related arrays together (e.g., networking, security, deployment)
• Use objects when needed: Don’t flatten structured data into strings
• Validate early: Use schema checks or assertions to catch malformed entries
• Document assumptions: Even constants may need context (e.g., “order matters”)

You can also layer arrays with functions or templates to generate variations:

# Generate policy statements for multiple buckets
locals {
  data_buckets = ["logs", "backups", "archive"]

  bucket_policies = [
    for name in local.data_buckets : {
      actions  = ["s3:GetObject"]
      resource = "arn:aws:s3:::${name}-bucket-*"
    }
  ]
}

Final Thoughts

Moving beyond scalar values to structured array constants transforms configuration from fragile lists of flags into a maintainable, expressive system. Whether you're defining policies, regions, feature flags, or deployment topologies, arrays let you model complexity cleanly.

The key is to treat configuration as data with structure, not just key-value pairs. Once you start thinking in arrays and objects, you’ll find your configs are easier to read, test, and evolve.

Basically, if you’re still using comma-separated strings to represent lists, it’s time to level up.

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