Make home volume creation optional

docs/production.md

@@ -58,7 +58,7 @@ and referenced from the `site` and `production` environments, e.g.:
 
     Note that:
         - Environment-specific variables (`cluster_name`) should be hardcoded
-          into the module block.
+          into the cluster module block.
         - Environment-independent variables (e.g. maybe `cluster_net` if the
           same is used for staging and production) should be set as *defaults*
           in `environments/site/tofu/variables.tf`, and then don't need to
@@ -76,17 +76,49 @@ and referenced from the `site` and `production` environments, e.g.:
   instances) it may be necessary to configure or proxy `chronyd` via an
   environment hook.
 
-- The cookiecutter provided OpenTofu configurations define resources for home and
-  state volumes. The former may not be required if the cluster's `/home` is
-  provided from an external filesystem (or Manila). In any case, in at least
-  the production environment, and probably also in the staging environment,
-  the volumes should be manually created and the resources changed to [data
-  resources](https://opentofu.org/docs/language/data-sources/). This ensures that even if the cluster is deleted via tofu, the
-  volumes will persist.
-
-  For a development environment, having volumes under tofu control via volume
-  resources is usually appropriate as there may be many instantiations
-  of this environment.
+- By default, the cookiecutter-provided OpenTofu configuration provisions two
+  volumes and attaches them to the control node:
+    - "$cluster_name-home" for NFS-shared home directories
+    - "$cluster_name-state" for monitoring and Slurm data
+  The volumes mean this data is persisted when the control node is rebuilt.
+  However if the cluster is destroyed with `tofu destroy` then the volumes will
+  also be deleted. This is undesirable for production environments and usually
+  also for staging environments. Therefore the volumes should be manually
+  created, e.g. via the CLI:
+
+      openstack volume create --size 200 mycluster-home # size in GB
+      openstack volume create --size 100 mycluster-state
+
+  and OpenTofu configured to use those volumes instead of managing them itself
+  by setting:
+
+      home_volume_provisioning = "attach"
+      state_volume_provisioning = "attach"
+
+  either for a specific environment within the cluster module block in
+  `environments/$ENV/tofu/main.tf`, or as the site default by changing the
+  default in `environments/site/tofu/variables.tf`.
+
+  For a development environment allowing OpenTofu to manage the volumes using
+  the default value of `"manage"` for those varibles is usually appropriate, as
+  it allows for multiple clusters to be created with this environment.
+
+  If no home volume at all is required because the home directories are provided
+  by a parallel filesystem (e.g. manila) set
+
+      home_volume_provisioning = "none"
+
+  In this case the NFS share for home directories is automatically disabled.
+
+  **NB:** To apply "attach" options to existing clusters, first remove the
+    volume(s) from the tofu state, e.g.:
+
+      tofu state list # find the volume(s)
+      tofu state rm 'module.cluster.openstack_blockstorage_volume_v3.state[0]'
+
+  This leaves the volume itself intact, but means OpenTofu "forgets" it. Then
+  set the "attach" options and run `tofu apply` again - this should show there
+  are no changes planned.
 
 - Enable `etc_hosts` templating:
 

environments/common/inventory/group_vars/all/nfs.yml

@@ -11,7 +11,7 @@ _nfs_node_ips: "{{ groups['nfs'] | map('extract', hostvars, 'ansible_host') | jo
 # default *all* entries in nfs_configurations to only permitting mounts from above IPs:
 nfs_export_clients: "{{ _nfs_node_ips }}"
 
-nfs_configurations:
+nfs_configuration_home_volume: # volume-backed home directories
   - comment: Export /exports/home from Slurm control node as /home
     nfs_enable:
         server:  "{{ inventory_hostname in groups['control'] }}"
@@ -25,8 +25,20 @@ nfs_configurations:
     # accidently overriden via default options
     nfs_export_options: 'rw,secure,root_squash'
 
+nfs_configuration_compute_nodes: # cluster configuration for compute_init/slurm-controlled rebuild
   - comment: Export /exports/cluster from Slurm control node
     nfs_enable:
         server: "{{ inventory_hostname in groups['control'] }}"
         clients: false
     nfs_export: "/exports/cluster"
+
+nfs_configurations_extra: [] # site-specific nfs shares
+
+nfs_configurations: >- # construct stackhpc.nfs variable
+  {{
+    nfs_configuration_home_volume if (cluster_home_volume | default(true)) else []
+    +
+    nfs_configuration_compute_nodes
+    +
+    nfs_configurations_extra
+  }}

environments/skeleton/{{cookiecutter.environment}}/tofu/control.tf

@@ -1,5 +1,9 @@
 locals {
-  control_volumes = concat([openstack_blockstorage_volume_v3.state], var.home_volume_size > 0 ? [openstack_blockstorage_volume_v3.home][0] : [])
+  control_volumes = concat(
+    # convert maps to lists with zero or one entries:
+    [for v in data.openstack_blockstorage_volume_v3.state: v],
+    [for v in data.openstack_blockstorage_volume_v3.home: v]
+  )
   nodename = templatestring(
     var.cluster_nodename_template,
     {
@@ -83,7 +87,7 @@ resource "openstack_compute_instance_v2" "control" {
 
     mounts:
       - [LABEL=state, ${var.state_dir}]
-      %{if var.home_volume_size > 0}
+      %{if var.home_volume_provisioning != "none"}
       - [LABEL=home, /exports/home]
       %{endif}
   EOF

environments/skeleton/{{cookiecutter.environment}}/tofu/inventory.tf

@@ -7,6 +7,7 @@ resource "local_file" "hosts" {
                             "login_groups": module.login
                             "compute_groups": module.compute
                             "state_dir": var.state_dir
+                            "cluster_home_volume": var.home_volume_provisioning != "none"
                           },
                           )
   filename = "../inventory/hosts.yml"

environments/skeleton/{{cookiecutter.environment}}/tofu/inventory.tpl

@@ -2,6 +2,7 @@ all:
     vars:
         openhpc_cluster_name: ${cluster_name}
         cluster_domain_suffix: ${cluster_domain_suffix}
+        cluster_home_volume: ${cluster_home_volume}
         cluster_compute_groups: ${jsonencode(keys(compute_groups))}
 
 control:

environments/skeleton/{{cookiecutter.environment}}/tofu/variables.tf

@@ -125,10 +125,38 @@ variable "state_volume_type" {
     default = null
 }
 
+variable "state_volume_provisioning" {
+    type = string
+    default = "manage"
+    description = <<-EOT
+        How to manage the state volume. Valid values are:
+            "manage": (Default) OpenTofu will create a volume "$cluster_name-state"
+                      and delete it when the cluster is destroyed. A volume
+                      with this name must not already exist. Use for demo and
+                      dev environments.
+            "attach": A single volume named "$cluster_name-state" must already
+                      exist. It is not managed by OpenTofu so e.g. is left
+                      intact if the cluster is destroyed. Use for production
+                      environments.
+        EOT
+    validation {
+      condition = contains(["manage", "attach"], var.state_volume_provisioning)
+      error_message = <<-EOT
+        home_volume_provisioning must be "manage" or "attach"
+    EOT
+    }
+}
+
 variable "home_volume_size" {
     type = number
-    description = "Size of state volume on control node, in GB"
-    default = 100 # GB, 0 means no home volume
+    description = "Size of state volume on control node, in GB."
+    default = 100
+    validation {
+        condition = var.home_volume_provisioning == "manage" ? var.home_volume_size > 0 : true
+        error_message = <<-EOT
+            home_volume_size must be > 0 when var.home_volume_provisioning == "manage"
+        EOT
+    }
 }
 
 variable "home_volume_type" {
@@ -137,6 +165,30 @@ variable "home_volume_type" {
     description = "Type of home volume, if not default type"
 }
 
+variable "home_volume_provisioning" {
+    type = string
+    default = "manage"
+    description = <<-EOT
+        How to manage the home volume. Valid values are:
+            "manage": (Default) OpenTofu will create a volume "$cluster_name-home"
+                      and delete it when the cluster is destroyed. A volume
+                      with this name must not already exist. Use for demo and
+                      dev environments.
+            "attach": A single volume named "$cluster_name-home" must already
+                      exist. It is not managed by OpenTofu so e.g. is left
+                      intact if the cluster is destroyed. Use for production
+                      environments.
+            "none":   No home volume is used. Use if /home is provided by
+                      a parallel filesystem, e.g. manila.
+        EOT
+    validation {
+      condition = contains(["manage", "attach", "none"], var.home_volume_provisioning)
+      error_message = <<-EOT
+        home_volume_provisioning must be one of "manage", "attach" or "none"
+    EOT
+    }
+}
+
 variable "vnic_types" {
     type = map(string)
     description = <<-EOT

environments/skeleton/{{cookiecutter.environment}}/tofu/volumes.tf

@@ -1,16 +1,59 @@
 resource "openstack_blockstorage_volume_v3" "state" {
+
+    # NB: Changes to this resource's "address" i.e. (label or for_each key)
+    # may lose state data for existing clusters using this volume
+
+    count = var.state_volume_provisioning == "manage" ? 1 : 0
+
     name = "${var.cluster_name}-state" # last word used to label filesystem
     description = "State for control node"
     size = var.state_volume_size
     volume_type = var.state_volume_type
 }
 
+data "openstack_blockstorage_volume_v3" "state" {
+
+/*  We use a data resource whether or not TF is managing the volume, so the
+    logic is all in one place. But that means this needs a dependency on the
+    actual resource to avoid a race.
+
+    Because there may be no volume, this has to use for_each.
+*/
+
+    for_each = toset(
+        (var.state_volume_provisioning == "manage") ?
+            [for v in openstack_blockstorage_volume_v3.state: v.name] :
+                ["${var.cluster_name}-state"]
+    )
+
+    name = each.key
+
+}
+
 resource "openstack_blockstorage_volume_v3" "home" {
 
-    count = var.home_volume_size > 0 ? 1 : 0
+    # NB: Changes to this resource's "address" i.e. (label or for_each key)
+    # may lose user data for existing clusters using this volume
+
+    count = var.home_volume_provisioning == "manage" ? 1 : 0
 
     name = "${var.cluster_name}-home"  # last word used to label filesystem
     description = "Home for control node"
     size = var.home_volume_size
     volume_type = var.home_volume_type
 }
+
+data "openstack_blockstorage_volume_v3" "home" {
+
+/*  Comments as for the state volume. */
+
+    for_each = toset(
+        (var.home_volume_provisioning == "manage") ?
+            [for v in openstack_blockstorage_volume_v3.home: v.name] :
+                (var.home_volume_provisioning == "attach") ?
+                    ["${var.cluster_name}-home"] :
+                        []
+    )
+
+    name = each.key
+}