OK, make opentofu work with external helper.

This was more complicated than I hoped for.
We could have done some HCL magic IF the openstack provider would have
allowed to query image properties by IDs which it does not seem to.
So the external python3 program is easiest and we reuse what we already
have.

Also comment on heat.

Signed-off-by: Kurt Garloff <[email protected]>

Author: garloff

user-docs/usage-hints/find-image/find_img.py

@@ -6,7 +6,7 @@
 #
 # (c) Kurt Garloff <[email protected]>, 7/2025
 # SPDX-License-Identifier: MIT
-"This module finds the a vanilla distribution image"
+"This module finds the a distribution image with a given purpose"
 
 import os
 import sys

user-docs/usage-hints/find-image/find_img.tf

@@ -1,5 +1,7 @@
 #!/usr/bin/env tofu apply -auto-approve
 # Pass variables with -var os_purpose=minimal
+# (c) Kurt Garloff <[email protected]>
+# SPDX-License-Identifier: MIT
 
 variable "os_distro" {
   type    = string
@@ -26,17 +28,20 @@ terraform {
 }
 
 provider "openstack" {
-  # Your cloud config (or use environment variables OS_CLOUD)
+  # Your cloud config (or use environment variable OS_CLOUD)
 }
 
 data "openstack_images_image_v2" "my_image" {
   most_recent = true
-  
+
   properties = {
-    os_distro        = "${var.os_distro}"
-    os_version       = "${var.os_version}"
-    os_purpose       = "${var.os_purpose}"
+    os_distro	  = "${var.os_distro}"
+    os_version    = "${var.os_version}"
+    os_purpose    = "${var.os_purpose}"
   }
+  #sort           = "name:desc,created_at:desc"
+  #sort_key       = "name"
+  #sort_direction = "desc"
 }
 
 # Output the results for inspection

user-docs/usage-hints/find-image/find_img2.py

@@ -0,0 +1,30 @@
+#!/usr/bin/env python3
+#
+# find_img2.py
+#
+# Find images for opentofu/terraform
+#
+# (c) Kurt Garloff <[email protected]>, 11/2025
+# SPDX-License-Identifier: MIT
+"This module finds the a distribution image with a given purpose"
+
+import sys
+import json
+import find_img
+
+try:
+    in_data = json.loads(sys.stdin.read())
+    conn = find_img.openstack.connect()  # cloud=os.environ["OS_CLOUD"])
+    images = find_img.find_image(conn, in_data["os_distro"], in_data["os_version"], in_data["os_purpose"])
+    for img in images:
+        print(f"DEBUG: {img[0]} {img[1]}", file=sys.stderr)
+    if not (len(images)):
+        print(f"No image found for {in_data}", file=sys.stderr)
+        sys.exit(1)
+    output = { "image_id": images[0][0],
+               "image_name": images[0][1] }
+    print(json.dumps(output))
+
+except Exception as e:
+    print(f"Error: {str(e)}", file=sys.stderr)
+    sys.exit(2)

user-docs/usage-hints/find-image/find_img2.tf

@@ -0,0 +1,52 @@
+#!/usr/bin/env tofu apply -auto-approve
+# Pass variables with -var os_purpose=minimal
+# (c) Kurt Garloff <[email protected]>
+# SPDX-License-Identifier: MIT
+
+variable "os_distro2" {
+  type    = string
+  default = "ubuntu"
+}
+
+variable "os_version2" {
+  type    = string
+  default = "24.04"
+}
+
+variable "os_purpose2" {
+  type    = string
+  default = "generic"
+}
+
+#terraform {
+#  required_providers {
+#    openstack = {
+#      source  = "terraform-provider-openstack/openstack"
+#      version = "~> 1.54.0"
+#    }
+#  }
+#}
+
+#provider "openstack" {
+#  # Your cloud config (or use environment variables OS_CLOUD)
+#}
+
+# Call python find_img.py to find best image
+data "external" "my_image2" {
+  program = ["python3", "${path.module}/find_img2.py"]
+
+  query = {
+    os_distro        = "${var.os_distro2}"
+    os_version       = "${var.os_version2}"
+    os_purpose       = "${var.os_purpose2}"
+  }
+}
+
+# Output the results for inspection
+output "selected_image2" {
+  value = {
+    id   = data.external.my_image2.result.image_id
+    name = data.external.my_image2.result.image_name
+  }
+}
+

user-docs/usage-hints/find-image/index.md

@@ -125,8 +125,9 @@ data "openstack_images_image_v2" "my_image" {
     os_version      = "24.04"
     os_purpose      = "generic"
   }
-  # sort_key        = "name"
-  # sort_direction  = "desc"
+  # sort             = "name:desc,created_at:desc"
+  # sort_key          = "name"
+  # sort_direction    = "desc"
 }
 
 # Use the selected image
@@ -138,11 +139,63 @@ resource "openstack_compute_instance_v2" "instance" {
 
 This will find the most recent image wtih the `os_` variables set to `ubuntu`, `24.04`, `generic`.
 Note that unlike the python and shell examples, we can not easily sort for name and creation
-date at the same time; the name sorting is thus commented out here. To use name sorting you can
-enable it — using it and then selecting the latest if the name is identical requires some
-HCL magic using `locals` and `reverse(sort(...))` calls or calling an external program.
+date at the same time; the only option to deal with several matches is to tell opentofu's
+openstack provider to return the latest (the one with the newest `created_at` date).
 
 An example can be found in [find_img.tf](find_img.tf). Call it with `tofu apply -auto-approve`
 (after you ran `tofu init` in this directory once).
 
-The fallback to name matching is harder.
+The fallback to name matching for clouds that don't have `os_purpose` yet is harder.
+
+We use an external program, the python script from before to select the right image and just create
+a little wrapper around it: [find_img2.py](find_img2.py). The HCL then looks like this:
+
+```hcl
+# Call python find_img.py to find best image
+data "external" "my_image2" {
+  program = ["python3", "${path.module}/find_img2.py"]
+
+  query = {
+    os_distro        = "${var.os_distro2}"
+    os_version       = "${var.os_version2}"
+    os_purpose       = "${var.os_purpose2}"
+  }
+}
+
+# Output the results for inspection
+output "selected_image2" {
+  value = {
+    id   = data.external.my_image2.result.image_id
+    name = data.external.my_image2.result.image_name
+  }
+}
+```
+
+Note that I have appended a `2` to the variable names, so they don't clash in case you have the
+original example in the same directory.
+
+## heat
+
+I did not find a good way to select an image based on its properties in heat.
+Obviously, you can use the python (or shell) script above and pass the image name
+or ID as a parameter when invoking heat.
+
+```yaml
+heat_template_version: 2018-08-31
+
+parameters:
+  image:
+    type: string
+    description: Image ID or name
+    constraints:
+      - custom_constraint: glance.image
+
+resources:
+  my_instance:
+    type: OS::Nova::Server
+    properties:
+      image: { get_param: image }
+      # ... other properties
+```
+
+and call `openstack stack create --parameter image=$ID $TEMPLATE $STACKNAME`.