Add a host_exporters role for the node and smartctl exporters and a host_firewall scrapers rule that opens exporter ports on wt0 to named source addresses

host_exporters/defaults/main.yml

@@ -0,0 +1,4 @@
+---
+# Adds prometheus-smartctl-exporter (trixie-backports) next to the node exporter
+# on hosts with physical disks.
+host_exporters_smart: false

host_exporters/tasks/main.yml

@@ -0,0 +1,69 @@
+---
+# Both exporters listen on all addresses; host_firewall limits who reaches them.
+- name: Install the node exporter
+  ansible.builtin.apt:
+    name: prometheus-node-exporter
+    state: present
+
+- name: Enable the node exporter
+  ansible.builtin.systemd:
+    name: prometheus-node-exporter
+    enabled: true
+    state: started
+  # Check mode does not install the package.
+  ignore_errors: "{{ ansible_check_mode }}"
+
+- name: Install the smartctl exporter
+  when: host_exporters_smart
+  block:
+    - name: Look for an existing backports source
+      ansible.builtin.shell: >-
+        grep -rEqs '^[^#]*{{ ansible_distribution_release }}-backports'
+        --include='*.list' --include='*.sources' --exclude=host-exporters-backports.sources /etc/apt
+      register: host_exporters_backports
+      changed_when: false
+      failed_when: host_exporters_backports.rc > 1
+      check_mode: false
+
+    # Backports stay at priority 100, so only packages named with default_release come from there.
+    - name: Add the backports source
+      ansible.builtin.copy:
+        dest: /etc/apt/sources.list.d/host-exporters-backports.sources
+        mode: "0644"
+        content: |
+          Types: deb
+          URIs: http://deb.debian.org/debian
+          Suites: {{ ansible_distribution_release }}-backports
+          Components: main
+          Signed-By: /usr/share/keyrings/debian-archive-keyring.gpg
+      register: host_exporters_source
+      when: host_exporters_backports.rc == 1
+
+    # The module rejects default_release while the release is missing from its package cache.
+    - name: Look for the backports release in the package lists
+      ansible.builtin.shell: apt-cache policy | grep -q 'n={{ ansible_distribution_release }}-backports'
+      register: host_exporters_lists
+      changed_when: false
+      failed_when: false
+      check_mode: false
+
+    - name: Refresh the package lists for the backports source
+      ansible.builtin.apt:
+        update_cache: true
+      when: host_exporters_lists.rc != 0
+
+    - name: Install the smartctl exporter from backports
+      ansible.builtin.apt:
+        name: prometheus-smartctl-exporter
+        default_release: "{{ ansible_distribution_release }}-backports"
+        state: present
+      # Check mode does not write the backports source.
+      ignore_errors: "{{ ansible_check_mode }}"
+
+    # The packaged unit runs as root, which smartctl needs for the disks.
+    - name: Enable the smartctl exporter
+      ansible.builtin.systemd:
+        name: smartctl_exporter
+        enabled: true
+        state: started
+      ignore_errors: "{{ ansible_check_mode }}"

host_firewall/defaults/main.yml

@@ -16,6 +16,12 @@ firewall:
   admin:
     v4: {}
     v6: {}
+  # Metrics scrapers: on wt0 only these source addresses reach the listed tcp
+  # ports (the vpn zone applies to every peer). Rendered only when both are set.
+  scrapers:
+    tcp: {}
+    v4: {}
+    v6: {}
   # Interface names (nft wildcards allowed) whose traffic is trusted.
   internal_ifaces: {}
   # Guest bridges (Proxmox vmbr*): DHCP, router solicitations and the public

host_firewall/templates/host.nft.j2

@@ -18,6 +18,7 @@ set {{ name }} {
 {% set guest_match = 'iifname { "' ~ (guest_ifaces | join('", "')) ~ '" }' %}
 {% set dnat = firewall.dnat | default({}, true) | dict2items | rejectattr('value', 'none') | map(attribute='value') | list %}
 {% set masquerade = firewall.masquerade | default({}, true) | dict2items | rejectattr('value', 'none') | map(attribute='value') | unique | list %}
+{% set scrapers = firewall.scrapers | default({}, true) %}
 {% set forward_guard = firewall.forward_guard | default({}, true) | dict2items | rejectattr('value', 'none') | list %}
 
 # Declare-then-delete makes every load one atomic transaction that replaces
@@ -36,6 +37,8 @@ table inet host {
 	{{ addr_set('admin_v6', 'ipv6_addr', firewall.admin.v6) }}
 	{{ addr_set('cluster_v4', 'ipv4_addr', cluster.v4) }}
 	{{ addr_set('cluster_v6', 'ipv6_addr', cluster.v6) }}
+	{{ addr_set('scrapers_v4', 'ipv4_addr', scrapers.v4) }}
+	{{ addr_set('scrapers_v6', 'ipv6_addr', scrapers.v6) }}
 	set ssh_meter_v4 {
 		type ipv4_addr; flags dynamic; timeout 10m; size 65535;
 	}
@@ -85,6 +88,14 @@ table inet host {
 	}
 
 	chain vpn {
+{% if list(scrapers.tcp) %}
+{% if list(scrapers.v4) %}
+		ip saddr @scrapers_v4 tcp dport { {{ list(scrapers.tcp) }} } accept
+{% endif %}
+{% if list(scrapers.v6) %}
+		ip6 saddr @scrapers_v6 tcp dport { {{ list(scrapers.tcp) }} } accept
+{% endif %}
+{% endif %}
 {% if list(firewall.vpn.tcp) %}
 		tcp dport { {{ list(firewall.vpn.tcp) }} } accept
 {% endif %}