Standardize resource names in Terraform scripts

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When starting a Terraform project for an Azure architecture, it's easy to come up with useful names for the resources in your architecture. They usually look like "my-resource-group', "my-public-ip", "my-vm", "mystorageaccount", and so on. When the architecture grows, or elements of it scale out, it becomes harder to design useful names that meet all requirements. This blog is about a tool that helps with this task.

If you agree with the above and just want a link to the tool, here it is: terraform-provider-azurecaf.

Usage samples are fully implemented in the scenarios folder of the github repo.

Everyone else, read on.

Requirements that must be met

• for each resource type, rules vary
  • length
  • accepted characters
  • accepted patterns (e.g. first character must be a lowercase alpha)
• It must be possible to override generated names in special cases
• It must be possible to generate globally unique names
• Generated names must behave like any other resource in tfstate
  • names persist across 'terraform apply' runs as long as name resource definition remains the same
  • name resources can be destroyed, tainted, etc just like any other terraform resource

Additional nice-to-have features

• a generated name should conform to a regular pattern that becomes familiar and instantly recognizable
• when there are many resources in list, it should be possible to instantly recognize resource types from the name
• clear and concise name generation code
• when an architecture grows or resources scale out horizontally, name generation follows naturally
• when testing permutations of resource properties, generating names is a very powerful enabling technique

Solution to the problem

The solution is a Terraform provider that generates resource names. Unsurprisingly, it meets all of the conditions above. Generated resource name configuration options include (in order of precedence):

• name - overrides other options
• slug - a few characters denoting the resource type
• random - randomly generated chars
• suffixes - an array of suffixes that are appended
• prefixes - an array of prefixes that are pre-pended

All configuration options are defined in the provider repo.

The following examples are fully implemented in the scenarios folder of the github repo.

Generates and implements a resource group name similar to rg-xxxxxxxx (very simple example)

resource "azurecaf_name" "rg_name" { resource_type = "azurerm_resource_group" random_length = 8 } resource "azurerm_resource_group" "rg" { name = azurecaf_name.rg_name.result location = "uksouth" } 

Generates and implements a log analytics workspace name (example of name override)

resource "azurecaf_name" "ws_name" { resource_type = "azurerm_log_analytics_workspace" random_length = 8 suffixes = ["local"] name = substr(data.azurerm_subscription.current.display_name, 0, 44) # desired outcome = log-<sub name>-xxxxxxxx-local # length = 3 + 1 + (44) + 1 + 8 + 1 + 5 = max of 63 characters for log analytics workspace name # 44 is the max # of chars to get from the subscription name in order to get everything else into the generated name # because the "name" parameter is an override, if more characters are used, other portions of the generated name will be truncated } resource "azurerm_log_analytics_workspace" "ws" { name = azurecaf_name.ws_name.result ... } 

The resource name rules (such as the max length of 63 characters) for azurerm_log_analytics_workspace are in this file.

Generates multiple singleton names with a single azurecaf_name resource

resource "azurecaf_name" "names" { resource_type = "azurerm_resource_group" resource_types = ["azurerm_lb", "azurerm_public_ip"] random_length = 4 } resource "azurerm_resource_group" "rg" { name = azurecaf_name.names.result location = "uksouth" } resource "azurerm_public_ip" "pip" { name = azurecaf_name.names.results["azurerm_public_ip"] ... } resource "azurerm_lb" "lb" { name = azurecaf_name.names.results["azurerm_lb"] ... } 

Generates a set of names per vm instance of a cluster of vms

resource "azurecaf_name" "per_instance" { count = var.number_of_servers resource_type = "azurerm_windows_virtual_machine" resource_types = ["azurerm_network_interface"] name = "websvr" random_length = 4 } resource "azurerm_network_interface" "nic" { count = var.number_of_servers name = azurecaf_name.per_instance[count.index].results["azurerm_network_interface"] ... } resource "azurerm_network_interface_backend_address_pool_association" "example" { count = var.number_of_servers network_interface_id = azurerm_network_interface.nic[count.index].id ... } resource "azurerm_windows_virtual_machine" "vm" { count = var.number_of_servers name = azurecaf_name.per_instance[count.index].result network_interface_ids = [ azurerm_network_interface.nic[count.index].id, ] ... }