Parameterise mount path for longhorn volume

agents.tf

@@ -192,10 +192,13 @@ resource "null_resource" "configure_longhorn_volume" {
   # Start the k3s agent and wait for it to have started
   provisioner "remote-exec" {
     inline = [
-      "mkdir /var/longhorn >/dev/null 2>&1",
-      "mount -o discard,defaults ${hcloud_volume.longhorn_volume[each.key].linux_device} /var/longhorn",
+      "set -e",
+      "mkdir -p '${each.value.longhorn_mount_path}' >/dev/null",
+      "mountpoint -q '${each.value.longhorn_mount_path}' || mount -o discard,defaults ${hcloud_volume.longhorn_volume[each.key].linux_device} '${each.value.longhorn_mount_path}'",
       "${var.longhorn_fstype == "ext4" ? "resize2fs" : "xfs_growfs"} ${hcloud_volume.longhorn_volume[each.key].linux_device}",
-      "echo '${hcloud_volume.longhorn_volume[each.key].linux_device} /var/longhorn ${var.longhorn_fstype} discard,nofail,defaults 0 0' >> /etc/fstab"
+      # Match any non-comment line (^[^#]) with any first field, followed by a space and your mount path in the second column.
+      # This prevents false positives like /data matching /data1.
+      "awk -v path='${each.value.longhorn_mount_path}' '$0 !~ /^#/ && $2 == path { found=1; exit } END { exit !found }' /etc/fstab || echo '${hcloud_volume.longhorn_volume[each.key].linux_device} ${each.value.longhorn_mount_path} ${var.longhorn_fstype} discard,nofail,defaults 0 0' | tee -a /etc/fstab >/dev/null"
     ]
   }
 

docs/customize-mount-path-longhorn.md

@@ -0,0 +1,108 @@
+## How to use a custom mount path for Longhorn
+<hr>
+
+In order to use NVMe and external disks with Longhorn, you may need to mount an external disk to a location other than the default under the `/var/` folder. This can provide more storage capacity across the cluster, especially if you haven't disabled the default Longhorn disks.
+
+> ⚠️ Note: You can set any mount path, but it must be within the `/var/` folder.
+
+### How to set a custom mount path for your external disk?
+
+1.  You must enable Longhorn in your module.
+    ```terraform
+    enable_longhorn = true
+    ```
+
+2.  Set the Helm values for Longhorn. The `defaultDataPath` is important as this path is automatically created by Longhorn and will be the default storage class pointing to your primary disks (e.g., NVMe).
+    ```yaml
+    longhorn_values = <<EOT
+    defaultSettings:
+      nodeDrainPolicy: allow-if-replica-is-stopped
+      defaultDataPath: /var/longhorn
+    persistence:
+      defaultFsType: ext4
+      defaultClassReplicaCount: 3
+      defaultClass: true
+    EOT
+    ```
+
+3.  In the `agent_nodepools` where you want to have a customized mount path, set the `longhorn_mount_path` variable.
+    ```terraform
+    agent_nodepools = [
+      {
+        # ... other nodepool configuration
+        labels               = ["role=monitoring", "storage=ssd"], # Label we use to filter nodes
+        longhorn_volume_size = 50,
+        longhorn_mount_path  = "/var/lib/longhorn" # This is the custom path
+      }
+    ]
+    ```
+
+4.  Apply the changes. As a result, your external disks will be mounted to `/var/lib/longhorn`.
+
+### How to configure Longhorn to use the new path?
+
+After setting the custom mount path, you need to configure Longhorn to recognize and use it. This typically involves:
+1.  Patching the Longhorn nodes to add the new disk.
+2.  Creating a new StorageClass that uses the new disk.
+
+Here is an example of how you can achieve this with Terraform:
+
+```terraform
+# Find the nodes with the 'ssd' storage label
+data "kubernetes_nodes" "ssd_nodes" {
+  metadata {
+    labels = {
+      "storage" = "ssd"
+    }
+  }
+}
+
+# Patch the selected Longhorn nodes to add the new disk
+resource "null_resource" "longhorn_patch_external_disk" {
+  for_each = {
+    for node in data.kubernetes_nodes.ssd_nodes.nodes : node.metadata[0].name => node.metadata[0].name
+  }
+
+  triggers = {
+    always_run = timestamp()
+  }
+
+  provisioner "local-exec" {
+    command = <<-EOT
+      KUBECONFIG=${var.kubeconfig_path} kubectl -n longhorn-system patch nodes.longhorn.io ${each.key} --type merge -p '{
+        "spec": {
+          "disks": {
+            "external-ssd": {
+              "path": "/var/lib/longhorn", # The path you set in the nodepools variable
+              "allowScheduling": true,
+              "tags": ["ssd"]
+            }
+          }
+        }
+      }'
+    EOT
+  }
+}
+
+# Create a new StorageClass for the SSD-backed Longhorn storage
+resource "kubernetes_manifest" "longhorn_ssd_storageclass" {
+  manifest = {
+    apiVersion = "storage.k8s.io/v1"
+    kind       = "StorageClass"
+    metadata = {
+      name = "longhorn-ssd"
+    }
+    provisioner = "driver.longhorn.io"
+    parameters = {
+      numberOfReplicas    = "3"
+      staleReplicaTimeout = "30"
+      diskSelector        = "ssd"
+      fromBackup          = ""
+    }
+    reclaimPolicy        = "Delete"
+    allowVolumeExpansion = true
+    volumeBindingMode    = "Immediate"
+  }
+
+  depends_on = [null_resource.longhorn_patch_external_disk]
+}

kube.tf.example

@@ -233,7 +233,9 @@ module "kube-hetzner" {
       # Something worth noting is that Volume storage is slower than node storage, which is achieved by not mentioning longhorn_volume_size or setting it to 0.
       # So for something like DBs, you definitely want node storage, for other things like backups, volume storage is fine, and cheaper.
       # longhorn_volume_size = 20
-
+      # Set any path inside /var/ folder to have the ability to use an additional storage class along with the default one, which by default must be set in helm values to
+      # /var/longhorn
+      # longhorn_mount_path = "/var/lib/longhorn"
       # Enable automatic backups via Hetzner (default: false)
       # backups = true
     },

locals.tf

@@ -259,6 +259,7 @@ locals {
         nodepool_name : nodepool_obj.name,
         server_type : nodepool_obj.server_type,
         longhorn_volume_size : coalesce(nodepool_obj.longhorn_volume_size, 0),
+        longhorn_mount_path : nodepool_obj.longhorn_mount_path,
         floating_ip : lookup(nodepool_obj, "floating_ip", false),
         floating_ip_rdns : lookup(nodepool_obj, "floating_ip_rdns", false),
         location : nodepool_obj.location,
@@ -288,6 +289,7 @@ locals {
           nodepool_name : nodepool_obj.name,
           server_type : nodepool_obj.server_type,
           longhorn_volume_size : coalesce(nodepool_obj.longhorn_volume_size, 0),
+          longhorn_mount_path : nodepool_obj.longhorn_mount_path,
           floating_ip : lookup(nodepool_obj, "floating_ip", false),
           floating_ip_rdns : lookup(nodepool_obj, "floating_ip_rdns", false),
           location : nodepool_obj.location,

variables.tf

@@ -242,6 +242,7 @@ variable "agent_nodepools" {
     labels                     = list(string)
     taints                     = list(string)
     longhorn_volume_size       = optional(number)
+    longhorn_mount_path        = optional(string, "/var/longhorn")
     swap_size                  = optional(string, "")
     zram_size                  = optional(string, "")
     kubelet_args               = optional(list(string), ["kube-reserved=cpu=50m,memory=300Mi,ephemeral-storage=1Gi", "system-reserved=cpu=250m,memory=300Mi"])
@@ -261,6 +262,7 @@ variable "agent_nodepools" {
       labels                     = optional(list(string))
       taints                     = optional(list(string))
       longhorn_volume_size       = optional(number)
+      longhorn_mount_path        = optional(string, null)
       swap_size                  = optional(string, "")
       zram_size                  = optional(string, "")
       kubelet_args               = optional(list(string), ["kube-reserved=cpu=50m,memory=300Mi,ephemeral-storage=1Gi", "system-reserved=cpu=250m,memory=300Mi"])
@@ -303,6 +305,22 @@ variable "agent_nodepools" {
     error_message = "Hetzner does not support networks with more than 100 servers."
   }
 
+  validation {
+    condition = alltrue(flatten([
+      for np in var.agent_nodepools : concat(
+        [
+          can(regex("^/var/$|^/var/([a-zA-Z0-9._-]+(/[a-zA-Z0-9._-]+)*)$", np.longhorn_mount_path))
+        ],
+        [
+          for node in values(coalesce(np.nodes, {})) : (
+            node.longhorn_mount_path == null || can(regex("^/var/$|^/var/([a-zA-Z0-9._-]+(/[a-zA-Z0-9._-]+)*)$", node.longhorn_mount_path))
+          )
+        ]
+      )
+    ]))
+    error_message = "Each longhorn_mount_path must start with '/var/', be a valid absolute path, and not end with a slash (except for '/var/'). This applies to both nodepool-level and node-level settings."
+  }
+
 }
 
 variable "cluster_autoscaler_image" {