Category: terraform

Official doc: https://www.terraform.io/docs/commands/console.html

“terraform console” is a command you can run, which gives you the opportunity to evaluate expressions and interpolation – very useful while building terraform.

To use it, on the command line, navigate to your terraform folder, and then run

terraform console

You will be met with this prompt (which doesn’t support any history through the “up” arrow key ?):

Here you can enter Terraform syntax and press enter to see the results.

Lets take a look at a resource group that exists in my configuration:

I entered in “azurerm_resource_group.mpn-trainlab-rg” and the console output all the properties in the state file for this resource.

I could further define my entry to a single property, and get this:

Now we can try this with some of our input variables. Lets say I have a complicated variable that I’m using to define disks, and I want to make sure when I reference that on a resource, its going to work:

data_disks = {
    ti-web = {
      count = 1
      size  = 64
      sku   = "Standard_LRS"
      caching = "ReadWrite"
    }
    production_u02 = {
      # Take the total data size you want, and divide it by the count of disks you want, to determine size
      count   = 4
      size    = 256
      sku     = "Premium_LRS" # Standard_LRS
      caching = "None"
    }
}

If I enter “var.data_disks” in the console, I would expect to get the exact same output as the code above, in JSON notation (lots of extra quotes and colons).

What if I’m trying to get the size of just the ti-web disk?

Looks like it works! Now I know on the resource for the “size” property, I can use “var.data_disks.ti-web.size” as a reference and it will provide my expected value.

A quick note to myself on how to get terraform plan output as a file.

By default running a “terraform plan” will output a nice graphical display of all expected changes. Sometimes you want to be able to distribute this as a file. In the past, I’ve tried commands like:

terraform plan > tfplan.txt

However that produces confusing output like this:

 

Instead, you can do this to get better output:

terraform plan -no-color > tfplan.txt

Now it will display in the console, and produce a text file that looks like this:

Today I needed a double for_each in my Terraform configuration; the ability to for_each over one thing, and at the same time for_each over another thing.

Here’s the context:

I want to produce two Azure Private DNS Zones, with records inside each of them, but conditionally. Think of it as ‘zones’ – zone A and zone B will be unique in their identifiers, but have commonalities in the IP addresses used.

I want do to this conditionally (a zone may not always exist) but also without repeating myself in code.

Lets start with a variable Map of my zones:

variable "zoneversions" {
  default = {
        "zonea" = {
            "zonename" = "a",
            "first3octets" = "10.9.3"
        },
        "zoneb" = {
            "zonename" = "b",
            "first3octets" = "10.9.4"
        }
    }
}

Here I’m creating an object that will work with for_each syntax. You’ll note I’m including additional attributes that are unique to each zone – this will come in handy later.

This variable allows me to create my Azure DNS private zones like this:

resource "azurerm_private_dns_zone" "zones-privatedns" {
  for_each            = var.zoneversions
  name                = "${each.value.zonename}.domain.com"
  resource_group_name = azurerm_resource_group.srv-rg.name
  }
}

This is using the “each.value” syntax, referencing the attributes of each zone. This terraform will produce the Private DNS zones described in the image above.

Now I want to populate each zone with records.
First, I’m going to use a local variable (could be a regular variable too) that will create a map of keys (common parts of server names) and values (last octet of the ip addresses):

locals {
  ipaddresses = {
    web                = ".3"
    rdp                = ".4"
    dc                 = ".10"
    db                 = ".11"
  }
}

For each zone that I have (a or b), I want to create a DNS record for each key in this map (hence the double for_each). Terraform won’t let you combine a for_each and count, and it doesn’t natively support 2 for_each expressions.

After a lot of trial and error (using terraform console to test) I came up with the code below. This article with a post by ‘apparentlysmart’ was a big help in the final task and helped me understand the structure of what I was trying to build.

I need 2 new local variables. The first will produce a flattened list of the combinations I’m looking for. And then since for_each only interacts with maps, I need a second local to convert it into that object type.

zonedips-list = flatten([ # Produce a list of maps, containing a name and IP address for each zone we specify in our variable
    for zones in var.zoneversions: [
      for servername,ips in local.ipaddresses: {
        zonename = "${zones.zonename}"
        name = "${zones.zonename}${servername}"
        ipaddress = "${zones.first3octets}${ips}"
      }
    ]
  ])

  zonedips-map = { # Take the list, and turn it into a map, so we can use it in a for_each
    for obj in local.zonedips-list : "${obj.name}" => obj # this means set the key of our new map to be $obj.name (hfx23-ti-web1) and => means keep the attributes of the object the same as the original
  }

Then I can use that second local when defining a single “azurerm_private_dns_a_record” resource:

resource "azurerm_private_dns_a_record" "vm-privaterecords" {
  for_each            = local.zonedips-map
  name                = each.value.name
  zone_name           = azurerm_private_dns_zone.zones-privatedns[each.value.zonename].name
  resource_group_name = azurerm_resource_group.srv-rg.name
  ttl                 = 300
  records             = [each.value.ipaddress]
}

This is where the magic happens. Because my map “zonedips-map” has attributes for each object, I can reference them with the ‘each.value’ syntax. So the name field of my DNS record will be equivalent to “${zones.zonename}${servername}”, or “aweb/bweb” as the for_each iterates. To place these in the correct zone, I’m using index selection on the resource, within the “zone_name” attribute – this says refer to the private_dns_zone with the terraform identifier “zones-privatedns” but an index (since there are multiple) that matches my version name.

This is where terraform console comes in real handy; I can produce a simple terraform config (without an AzureRM provider) that contains these items, with either outputs, or a placeholder resource (like a file).

For example, take the terraform configuration below, do a “terraform init” on it, and then “terraform console” command.

terraform {
  backend "local" {
  }
}

locals {
  zonedips-list = flatten([
    for zones in var.zoneversions: [
      for servername,ips in local.ipaddresses: {
        zonename = "${zones.zonename}"
        name = "${zones.zonename}${servername}"
        ipaddress = "${zones.first3octets}${ips}"
      }
    ]
  ])

  zonedips-map = {
    for obj in local.zonedips-list : "${obj.name}" => obj
  }

  ipaddresses = {
    web                = ".3"
    rdp                = ".4"
    dc                 = ".10"
    db                 = ".11"
  }
}

variable "zoneversions" {
  default = {
        "zonea" = {
            "zonename" = "a",
            "first3octets" = "10.9.3"
        },
        "zoneb" = {
            "zonename" = "b",
            "first3octets" = "10.9.4"
        }
    }
}

resource "local_file" "test" {
    for_each = local.zonedips-map
    filename    = each.value.name
    content     = each.value.ipaddress
}

You can then explore and display the contents of the variables or locals by calling them explicitly in the console:

So we can display the contents of our flattened list:

And then the produced map:

 

Finally, we can do a “terraform plan”, and look at the file resources that would be created (I shrunk this down to just 2 items for brevity):

You can see the key here in the ‘content’ and ‘filename’ attributes.