feat: monitoring — node_exporter + ROCm sysfs collector + alertmanager webhook

Ansible roles:
- node_exporter : déploie node_exporter v1.9.1 sur storage-01 et gpu-01
  avec textfile collector + services systemd. ROCm activé sur gpu-01 uniquement
  via group_vars. Collecte métriques GPU via sysfs (temp, VRAM, utilisation)
  — pas de dépendance rocm-smi (remplacé dans ROCm 7.x)
- alertmanager_webhook : service Python sur storage-01 (:9093/webhook)
  reçoit alertes AlertManager et les route vers ask-agent monitor → Hermes

Playbooks: node_exporter + alertmanager_webhook ajoutés à storage-01 et gpu-01

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

ansible/roles/node_exporter/tasks/main.yml

@@ -0,0 +1,86 @@
+---
+- name: Create node_exporter user
+  ansible.builtin.user:
+    name: "{{ node_exporter_user }}"
+    shell: /sbin/nologin
+    create_home: false
+    system: true
+    state: present
+
+- name: Create textfile collector directory
+  ansible.builtin.file:
+    path: "{{ node_exporter_textfile_dir }}"
+    state: directory
+    owner: "{{ node_exporter_user }}"
+    group: "{{ node_exporter_user }}"
+    mode: '0755'
+
+- name: Download node_exporter
+  ansible.builtin.get_url:
+    url: "https://github.com/prometheus/node_exporter/releases/download/v{{ node_exporter_version }}/node_exporter-{{ node_exporter_version }}.linux-amd64.tar.gz"
+    dest: "/tmp/node_exporter-{{ node_exporter_version }}.tar.gz"
+    mode: '0644'
+
+- name: Extract node_exporter
+  ansible.builtin.unarchive:
+    src: "/tmp/node_exporter-{{ node_exporter_version }}.tar.gz"
+    dest: /tmp/
+    remote_src: true
+    creates: "/tmp/node_exporter-{{ node_exporter_version }}.linux-amd64/node_exporter"
+
+- name: Install node_exporter binary
+  ansible.builtin.copy:
+    src: "/tmp/node_exporter-{{ node_exporter_version }}.linux-amd64/node_exporter"
+    dest: /usr/local/bin/node_exporter
+    owner: root
+    group: root
+    mode: '0755'
+    remote_src: true
+
+- name: Deploy node_exporter systemd service
+  ansible.builtin.template:
+    src: node_exporter.service.j2
+    dest: /etc/systemd/system/node_exporter.service
+    mode: '0644'
+  notify: Restart node_exporter
+
+- name: Enable and start node_exporter
+  ansible.builtin.systemd:
+    name: node_exporter
+    enabled: true
+    state: started
+    daemon_reload: true
+
+- name: Open node_exporter port in nftables
+  ansible.builtin.lineinfile:
+    path: /etc/nftables.conf
+    insertafter: '# prometheus'
+    line: "    tcp dport {{ node_exporter_port }} accept comment \"node_exporter\""
+    state: present
+  notify: Reload nftables
+  ignore_errors: true
+
+- name: Deploy ROCm scraper script
+  ansible.builtin.template:
+    src: rocm_scraper.sh.j2
+    dest: /usr/local/bin/rocm_scraper.sh
+    mode: '0755'
+  when: rocm_exporter_enabled
+
+- name: Deploy ROCm scraper service + timer
+  ansible.builtin.template:
+    src: "{{ item }}.j2"
+    dest: "/etc/systemd/system/{{ item }}"
+    mode: '0644'
+  loop:
+    - rocm_scraper.service
+    - rocm_scraper.timer
+  when: rocm_exporter_enabled
+
+- name: Enable ROCm scraper timer
+  ansible.builtin.systemd:
+    name: rocm_scraper.timer
+    enabled: true
+    state: started
+    daemon_reload: true
+  when: rocm_exporter_enabled