[Terraform] Use “IF/ELSE” through the Merge function in Terraform

1) “IF/ELSE” with the Merge function

From the code snippet you’ve provided, it seems like you’re working with Terraform to create an AWS EKS (Elastic Kubernetes Service) cluster along with various node groups, including an “extra” node group. You’ve mentioned that the extra node group is still created even though you’ve set the variable extra_node_group to false.

Based on the provided code, here’s a detailed analysis:

1. Variable Definition: You’ve defined a variable extra_node_group with a default value of false.

   variable "extra_node_group" {
     description = "When you want to create an extra node group for the special purpose"
     type    = bool
     default = false  # Set to true to enable the extra_node_group, or false to disable it
   }

2. Usage in the Code: However, there is no condition in your code that checks the value of var.extra_node_group to determine whether or not to create the extra node group. The code snippet you provided is defining the extra node group within the self_managed_node_groups block without any conditional logic.

   self_managed_node_groups = {
     extra = {
       count = var.extra_node_group ? 1 : 0
       platform = "linux"
       name = "extra"
       ...
     }
     ...
   }

3. Possible Cause: The issue is that in Terraform, the count argument is used at the resource level to determine how many instances of that resource to create, but you’re using it inside a map where it doesn’t have the desired effect.

Solution:

You can fix this issue by restructuring your code to use a conditional expression that controls the creation of the extra node group. Here’s an example modification to the code:

self_managed_node_groups = merge(
  {
    linux = {
      ...
    }
    windows = {
      ...
    }
  },
  var.extra_node_group ? {
    extra = {
      platform = "linux"
      name = "extra"
      ...
    }
  } : {}
)

In this example, the merge function is used to conditionally include the “extra” node group only if var.extra_node_group is true. If var.extra_node_group is false, an empty map is merged, effectively omitting the “extra” node group from the final configuration.

Make sure to adjust the rest of your code accordingly to match this structure.

This approach leverages Terraform’s conditional expressions and map handling to achieve the desired behavior of conditionally creating the extra node group based on the value of the extra_node_group variable.

Và bạn có thể học thêm ở Video dưới

2) “IF/ELSE” to insert values template terraform

block_device_mappings = [
          {
            device_name = ng.platform == "windows" ? "/dev/sda1" : "/dev/xvda",
            ebs = {
              volume_size           = 100
              volume_type           = "gp3"
              iops                  = 3000
              throughput            = 125
              encrypted             = true
              delete_on_termination = true
            }
          }
        ]

ở đây chỉ đơn giản nếu windows thí đưa value “/dev/sda1” còn lại là /dev/xvda

        tags = {
          "k8s.io/cluster-autoscaler/enabled"                 = "true",
          "k8s.io/cluster-autoscaler/${var.eks_cluster_name}" = "owned"
        }

        taints = ng.taints
        labels = ng.labels

        # Conditional AMI type based on the platform
        ami_type = ng.platform == "windows" ? var.windows_ami_type : null,
        instance_types = [ng.instance_type]
        min_size       = ng.min_size
        max_size       = ng.max_size
        desired_size   = ng.desired_size
        key_name = var.node_host_key_name

Còn 1 case khác là: nếu ng.platform == “windows” thì đưa value của var.windows_ami_type vào.