Terraform Iterators

1. Using for_each on a list of strings:

    locals {
      ip_addresses = ["10.0.0.1", "10.0.0.2"]
    }
   
    resource "example" "example" {
      for_each   = toset(local.ip_addresses)
      ip_address = each.key
    }
   

2. Using for_each on a list of objects

    locals {
      virtual_machines = [
        {
          ip_address = "10.0.0.1"
          name       = "vm-1"
        },
        {
          ip_address = "10.0.0.1"
          name       = "vm-2"
        }
      ]
    }    
   
    resource "example" "example" {
      for_each   = {
        for index, vm in local.virtual_machines:
        vm.name => vm
      }
      name       = each.value.name
      ip_address = each.value.ip_address
    }
   

3. Using for_each to combine two lists

    locals {
      domains = [
        "https://abc.com",
        "https://def.com"
      ]
      paths = [
        "/one",
        "/two",
        "/three"
      ]
    }
           
    resource "example" "example" {
      # Loop over both lists and flatten the result
      urls = flatten([
        for domain in local.domains : [
          for path in local.paths : {
            domain = domain
            path   = path
          }
        ]
      ])
    }
   

4. Using for_each on a nested block

    # Using the optional() keyword makes fields null if not present
    variable "routes" {
      type = list(
        name   = string
        path   = string
        config = optional(object({
          cache_enabled = bool
          https_only    = bool
        }))
      default = []
    }
   
    resource "example" "example" {
      name = ...
         
      dynamic "route" {
        for_each = {
          for route in var.routes :
          route.name => route
        }
        content {
          # Note: <top_level_block>.value.<object_key>
          name = route.value.name
        }
           
        dynamic "configuration" {
          # Note: <top_level_block>.value.<optional_object_key>
          for_each = route.value.config != null ? [1] : []
          content {
            cache_enabled = route.value.config.cache_enabled
            https_only    = route.value.config.https_only
          }
        }
      }
   

5. Using for_each as a conditional

``` variable “deploy_example” { type = bool description = “Indicates whether to deploy something.” default = true }

# Using count and a conditional, for_each is also possible here.
# See the next solution using a for_each with a conditional.
resource "example" "example" {
  count      = var.deploy_example ? 0 : 1
  name       = ...
  ip_address = ...
}

variable "enable_logs" {
  type        = bool
  description = "Indicates whether to enable something."
  default     = false
}

resource "example" "example" {
  name       = ...
  ip_address = ...

  # Note: dynamic blocks cannot use count!
  # Using for_each with an empty list and list(1) as a readable alternative. 
  dynamic "logs" {
    for_each = var.enable_logs ? [] : [1]
    content {
      name     = "logging"
    }
  }
}
```