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The count meta-argument in Terraform lets you create multiple instances of the same resource from a single resource block. It uses a zero-based numeric index (count.index) that you can reference inside the resource to produce unique names, tags, or other per-instance values. This makes count ideal when you need several identical or nearly-identical resources, or when the number of instances should be driven by a variable.
Use count when you want to scale identical resources by number. For stable identities or keyed collections, consider for_each instead (see the comparison below).
The image explains the count meta-argument in Terraform, which allows creating multiple instances of a resource using a single block, assigns an index to each instance, and describes how to reference the resource.

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How count works

  • Set count to a number or a numeric variable (for example, var.vm_count).
  • Terraform creates that many instances and assigns each a numeric index starting at 0.
  • Inside the resource you can reference count.index to create unique values per instance.
  • To address an individual instance from another resource or an output, use an index on the resource address (for example: aws_instance.example[1]).
Example: create multiple Azure VMs driven by a variable and use count.index to generate unique names. 
variable "vm_count" {
  type    = number
  default = 3
}

resource "azurerm_virtual_machine" "example" {
  count               = var.vm_count
  name                = "vm-${count.index}"
  location            = "East US"
  resource_group_name = "my-resource-group"
  vm_size             = "Standard_D2s_v3"

  os_profile {
    computer_name  = "vm-${count.index}"
    admin_username = "adminuser"
  }
}
With vm_count = 3, Terraform will create VMs named vm-0, vm-1, and vm-2.

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Referencing instances

  • Address the first instance: azurerm_virtual_machine.example[0]
  • Get the name of the second instance: azurerm_virtual_machine.example[1].name
  • Collect all names into an output:
output "vm_names" {
  value = azurerm_virtual_machine.example[*].name
}

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Common uses and tips

  • Use count.index inside name, tags, or properties that accept strings to ensure uniqueness.
  • Combine count with other functions (for example, count = var.vm_count > 0 ? var.vm_count : 0) to handle conditional creation.
  • Avoid using count with resources that require stable identity across changes if individual items will be added/removed frequently — the numeric indexing can shift.

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count vs for_each

Featurecountfor_each
IndexingNumeric, zero-based count.indexKeyed by element value or map keys
Stable identityNo — indices shift if items are inserted/removedYes — each key maps to a stable instance
Use-caseCreate N identical instances, scale by a numberCreate instances from a set/map where identity matters
Examplecount = var.vm_countfor_each = toset(["a","b","c"])

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When to prefer for_each

If you need stable, predictable identities for each instance (for example, when adding/removing single items), for_each is usually safer because it keys resources by a set or map value instead of a shifting numeric index.
Because count is index-based, changing the number or ordering of instances can shift indices and cause Terraform to delete and recreate resources. If you need stable identities for resources, prefer for_each.

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References

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