Fix Bookworm DHCP search domain issue

.pre-commit-config.yaml

@@ -130,6 +130,8 @@ repos:
     rev: v1.5.1
     hooks:
       - id: mypy
+        additional_dependencies:
+          - types-pyyaml
   - repo: https://github.com/asottile/pyupgrade
     rev: v3.10.1
     hooks:

cloud_init.tf

@@ -38,6 +38,47 @@ data "cloudinit_config" "cloud_init_tasks" {
     merge_type   = "list(append)+dict(recurse_array)+str()"
   }
 
+  # TODO: Remove the following two parts when and if that becomes
+  # possible.  See #96 for more details.
+
+  # Fix the DHCP options in the Canonical Netplan configuration
+  # created by cloud-init.
+  #
+  # The issue is that Netplan uses a default of false for
+  # dhcp4-overrides.use-domains, and cloud-init does not explicitly
+  # set this key or provide any way to do so.
+  #
+  # See these issues for more details:
+  # - cisagov/skeleton-packer#300
+  # - canonical/cloud-init#4764
+  part {
+    content = templatefile(
+      "${path.module}/cloudinit/fix-dhcp.tpl.py", {
+        netplan_config = "/etc/netplan/50-cloud-init.yaml"
+    })
+    content_type = "text/x-shellscript"
+    filename     = "fix-dhcp.py"
+    merge_type   = "list(append)+dict(recurse_array)+str()"
+  }
+
+  # Now that the DHCP options in the Canonical Netplan configuration
+  # created by cloud-init have been fixed, reapply the Netplan
+  # configuration.
+  #
+  # The issue is that Netplan uses a default of false for
+  # dhcp4-overrides.use-domains, and cloud-init does not explicitly
+  # set this key or provide any way to do so.
+  #
+  # See these issues for more details:
+  # - cisagov/skeleton-packer#300
+  # - canonical/cloud-init#4764
+  part {
+    content      = file("${path.module}/cloudinit/fix-dhcp.yml")
+    content_type = "text/cloud-config"
+    filename     = "fix-dhcp.yml"
+    merge_type   = "list(append)+dict(recurse_array)+str()"
+  }
+
   part {
     filename     = "openvpn-config.yml"
     content_type = "text/cloud-config"

cloudinit/fix-dhcp.tpl.py

@@ -0,0 +1,37 @@
+#!/usr/bin/env python3
+
+"""Append the necessary DHCP options to the Netplan configuration.
+
+The Netplan configuration is created by cloud-init, but it needs to be
+slightly modified and reapplied.  This script takes care of the
+modification.
+
+See these issues for more details:
+- cisagov/skeleton-packer#300
+- canonical/cloud-init#4764
+
+This file is a template.  It should be processed by Terraform.
+
+"""
+
+# TODO: Remove this script when and if that becomes possible.  See #96
+# for more details.
+
+# Third-Party Libraries
+import yaml
+
+# Inputs from Terraform
+NETPLAN_CONFIG = "${netplan_config}"
+
+with open(NETPLAN_CONFIG) as f:
+    # Load the current Netplan configuration
+    config = yaml.safe_load(f)
+    # Add a dhcp4-overrides section to each network
+    config["network"]["ethernets"] = {
+        k: v | {"dhcp4-overrides": {"use-domains": True}}
+        for (k, v) in config["network"]["ethernets"].items()
+    }
+
+# Write the results back out to the Netplan configuration file
+with open(NETPLAN_CONFIG, "w") as f:
+    f.write(yaml.dump(config))

cloudinit/fix-dhcp.yml

@@ -0,0 +1,10 @@
+---
+
+# There is a Python script that fixes the DHCP4 options in the netplan
+# configuration already generated by cloud-init.  The following simply
+# reapplies the Netplan configuration after the modification.
+#
+# TODO: Remove this code when and if that becomes possible.  See #96
+# for more details.
+runcmd:
+  - [netplan, apply]