diff --git a/terraform/projects/kubernetes_vms/main.tf b/terraform/projects/kubernetes_vms/main.tf
index e4a05d3..43a6160 100644
--- a/terraform/projects/kubernetes_vms/main.tf
+++ b/terraform/projects/kubernetes_vms/main.tf
@@ -1,72 +1,170 @@
+data "proxmox_virtual_environment_nodes" "pve_nodes" {}
+
+locals {
+  # ---------------------------------------------------------------------------
+  # Proxmox nodes online + available memory
+  # ---------------------------------------------------------------------------
+
+  node_stats = {
+    for i, name in data.proxmox_virtual_environment_nodes.pve_nodes.names :
+    name => floor(
+      data.proxmox_virtual_environment_nodes.pve_nodes.memory_available[i]
+      / 1024
+      / 1024
+    )
+    if data.proxmox_virtual_environment_nodes.pve_nodes.online[i]
+  }
+
+  # ---------------------------------------------------------------------------
+  # Nodes ordered by available memory, most available first
+  # ---------------------------------------------------------------------------
+
+  max_free_mib = length(local.node_stats) > 0
+    ? max(values(local.node_stats)...)
+    : 0
+
+  node_order = [
+    for key in sort([
+      for node, free_mib in local.node_stats :
+      "${format("%012d", local.max_free_mib - free_mib)}|${node}"
+    ]) :
+    split("|", key)[1]
+  ]
+
+  # ---------------------------------------------------------------------------
+  # VM layout
+  # ---------------------------------------------------------------------------
+
+  vm_layout = flatten([
+    for role in ["master", "worker"] : [
+      for i in range(
+        role == "master"
+        ? var.master_count
+        : var.worker_count
+      ) : {
+        vm_name = "kub-${var.vm_env}-${substr(role, 0, 1)}${format("%02d", i + 1)}"
+
+        seq_index = (
+          role == "master"
+          ? 0
+          : var.master_count
+        ) + i
+
+        vm_role = role
+      }
+    ]
+  ])
+
+  # ---------------------------------------------------------------------------
+  # Nodes with enough memory for each VM type
+  # ---------------------------------------------------------------------------
+
+  master_nodes = [
+    for node in local.node_order :
+    node
+    if local.node_stats[node] >= var.vm_attr.master.ram
+  ]
+
+  worker_nodes = [
+    for node in local.node_order :
+    node
+    if local.node_stats[node] >= var.vm_attr.worker.ram
+  ]
+
+  # ---------------------------------------------------------------------------
+  # VM list
+  # ---------------------------------------------------------------------------
+
+  vm_list = {
+    for vm in local.vm_layout :
+    vm.vm_name => {
+      node_name = (
+        vm.vm_role == "master"
+        ? local.master_nodes
+        : local.worker_nodes
+      )[
+        vm.seq_index % length(
+          vm.vm_role == "master"
+          ? local.master_nodes
+          : local.worker_nodes
+        )
+      ]
+
+      vm_cpu  = var.vm_attr[vm.vm_role].cpu
+      vm_ram  = var.vm_attr[vm.vm_role].ram
+      vm_vlan = var.vm_attr[vm.vm_role].vlan
+      vm_role = vm.vm_role
+    }
+  }
+
+  roles = toset([
+    for vm in local.vm_list :
+    vm.vm_role
+  ])
+}
+
 module "pve_vm" {
-  source    = "../../modules/pve_vm"
-  for_each  = local.vm_list
+  source   = "../../modules/pve_vm"
+  for_each = local.vm_list
+
   node_name = each.value.node_name
   vm_name   = each.key
   vm_cpu    = each.value.vm_cpu
   vm_ram    = each.value.vm_ram
   vm_vlan   = each.value.vm_vlan
-  vm_tags   = ["${var.vm_env}"]
+  vm_tags   = [var.vm_env]
 }
 
-locals {
-  node_stats = [
-    for i, name in data.proxmox_virtual_environment_nodes.pve_nodes.names : {
-      name     = name
-      free_mib = floor(data.proxmox_virtual_environment_nodes.pve_nodes.memory_available[i] / 1024 / 1024)
-    }
-    if data.proxmox_virtual_environment_nodes.pve_nodes.online[i]
-  ]
-
-  max_free_mib = length(local.node_stats) > 0 ? max([for node in local.node_stats : node.free_mib]...) : 0
-
-  # Online nodes ordered by available memory, most available first (name as tie-break)
-  node_order = [
-    for key in sort([
-      for node in local.node_stats : "${format("%012d", local.max_free_mib - node.free_mib)}|${node.name}"
-    ]) : split("|", key)[1]
-  ]
-
-  vm_layout = flatten([
-    for role in ["master", "worker"] : [
-      for i in range(role == "master" ? var.master_count : var.worker_count) : {
-        vm_name   = "kub-${var.vm_env}-${substr(role, 0, 1)}${format("%02d", i + 1)}"
-        seq_index = (role == "master" ? 0 : var.master_count) + i
-        vm_role   = role
-      }
-    ]
-  ])
-
-  vm_list = {
-    for vm in local.vm_layout :
-    vm.vm_name => {
-      node_name = length(local.node_order) > 0 ? local.node_order[vm.seq_index % length(local.node_order)] : ""
-      vm_cpu    = var.vm_attr[vm.vm_role].cpu
-      vm_ram    = var.vm_attr[vm.vm_role].ram
-      vm_vlan   = var.vm_attr[vm.vm_role].vlan
-      vm_role   = vm.vm_role
-    }
-  }
-
-  roles = toset([for vm in local.vm_list : vm.vm_role])
-}
-
-data "proxmox_virtual_environment_nodes" "pve_nodes" {}
-
 output "vm_ip" {
-  value = { for k, v in module.pve_vm : k => v.vm_ip }
+  value = {
+    for k, v in module.pve_vm :
+    k => v.vm_ip
+  }
 }
 
 resource "ansible_group" "vm_groups" {
   for_each = local.roles
-  name     = each.key
+
+  name = each.key
 }
 
 resource "ansible_host" "vm_hosts" {
   for_each = module.pve_vm
-  name     = each.key
+
+  name = each.key
+
   variables = {
     ansible_host = each.value.vm_ip
   }
-  groups = [local.vm_list[each.key].vm_role]
+
+  groups = [
+    local.vm_list[each.key].vm_role
+  ]
+}
+
+resource "terraform_data" "validate_vm_placement" {
+  input = {
+    master_nodes = length(local.master_nodes)
+    worker_nodes = length(local.worker_nodes)
+  }
+
+  lifecycle {
+    precondition {
+      condition = (
+        var.master_count == 0 ||
+        length(local.master_nodes) > 0
+      )
+
+      error_message = "No online Proxmox node has enough RAM for a master VM."
+    }
+
+    precondition {
+      condition = (
+        var.worker_count == 0 ||
+        length(local.worker_nodes) > 0
+      )
+
+      error_message = "No online Proxmox node has enough RAM for a worker VM."
+    }
+  }
 }
\ No newline at end of file