Ansible-roles/host_exporters/tasks/main.yml

---
# Both exporters listen on all addresses; host_firewall limits who reaches them.
# Its recommends (smartmontools, nvme-cli, ipmitool) start units that fail on hosts without such hardware.
- name: Install the node exporter
  ansible.builtin.apt:
    name: prometheus-node-exporter
    install_recommends: false
    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 }}"

# Reads the BMC through /dev/ipmi0, read-only: no raw commands, no configuration.
# FreeIPMI refuses in-band access for any uid but 0, so the exporter runs as the packaged
# unprivileged user prometheus and starts the FreeIPMI tools it needs through sudo.
- name: Install the IPMI exporter
  when: host_exporters_ipmi
  block:
    - name: Install ipmitool and the IPMI exporter
      ansible.builtin.apt:
        name:
          - ipmitool
          - sudo
          - prometheus-ipmi-exporter
        install_recommends: false
        state: present

    - name: Allow the exporter user to run the FreeIPMI tools
      ansible.builtin.copy:
        dest: /etc/sudoers.d/prometheus-ipmi-exporter
        mode: "0440"
        validate: visudo -cf %s
        content: |
          Defaults:prometheus !pam_session
          {% for collector in host_exporters_ipmi_collectors %}
          prometheus ALL = (root) NOPASSWD: /usr/sbin/{{ host_exporters_ipmi_tools[collector].tool }} {{ host_exporters_ipmi_tools[collector].args }} --config-file {{ host_exporters_ipmi_freeipmi_conf }}
          {% endfor %}
      register: host_exporters_ipmi_sudo

    - name: Create the FreeIPMI configuration directory
      ansible.builtin.file:
        path: "{{ host_exporters_ipmi_freeipmi_conf | dirname }}"
        state: directory
        owner: root
        group: root
        mode: "0755"

    # See the defaults for why the file is static.
    - name: Write the FreeIPMI configuration
      ansible.builtin.copy:
        dest: "{{ host_exporters_ipmi_freeipmi_conf }}"
        owner: root
        group: root
        mode: "0644"
        content: |
          # In-band access needs no settings. Not even sdr-cache-directory: the tools without an SDR cache
          # reject it, and the cache of the ipmi tool stays in the home of root.

    # collector_cmd replaces the tool itself, so each collector gets a wrapper that adds sudo. It swaps
    # the exporter's --config-file for the static one. The exporter fills a named pipe at the path it
    # passes and waits for a reader; the wrapper drains it so that writer does not hang.
    - name: Create the sudo wrappers directory
      ansible.builtin.file:
        path: /usr/local/libexec/ipmi-exporter
        state: directory
        mode: "0755"

    - name: Write the sudo wrappers
      ansible.builtin.copy:
        dest: /usr/local/libexec/ipmi-exporter/{{ item.key }}
        mode: "0755"
        content: |
          #!/bin/sh
          n=$#
          while [ "$n" -gt 0 ]; do
            a=$1; shift; n=$((n - 1))
            if [ "$a" = --config-file ] && [ "$n" -gt 0 ]; then
              timeout 5 cat "$1" > /dev/null 2>&1
              shift; n=$((n - 1))
            else
              set -- "$@" "$a"
            fi
          done
          exec sudo -n /usr/sbin/{{ item.value.tool }} "$@" --config-file {{ host_exporters_ipmi_freeipmi_conf }}
      loop: "{{ host_exporters_ipmi_tools | dict2items | selectattr('key', 'in', host_exporters_ipmi_collectors) | list }}"
      loop_control:
        label: "{{ item.key }}"
      register: host_exporters_ipmi_wrappers

    - name: Write the IPMI exporter configuration
      ansible.builtin.copy:
        dest: /etc/prometheus/ipmi-local.yml
        mode: "0644"
        content: |
          modules:
            default:
              collectors:
          {% for collector in host_exporters_ipmi_collectors %}
                - {{ collector }}
          {% endfor %}
              collector_cmd:
          {% for collector in host_exporters_ipmi_collectors %}
                {{ collector }}: /usr/local/libexec/ipmi-exporter/{{ collector }}
          {% endfor %}
      register: host_exporters_ipmi_config

    - name: Create the IPMI exporter unit drop-in directory
      ansible.builtin.file:
        path: /etc/systemd/system/prometheus-ipmi-exporter.service.d
        state: directory
        mode: "0755"

    # sudo needs setuid, so NoNewPrivileges stays off.
    - name: Run the IPMI exporter with that configuration
      ansible.builtin.copy:
        dest: /etc/systemd/system/prometheus-ipmi-exporter.service.d/local.conf
        mode: "0644"
        content: |
          [Service]
          ExecStart=
          ExecStart=/usr/bin/prometheus-ipmi-exporter --config.file=/etc/prometheus/ipmi-local.yml
      register: host_exporters_ipmi_unit

    - name: Enable the IPMI exporter
      ansible.builtin.systemd:
        name: prometheus-ipmi-exporter
        enabled: true
        state: "{{ 'restarted' if (host_exporters_ipmi_config.changed or host_exporters_ipmi_unit.changed or host_exporters_ipmi_wrappers.changed) else 'started' }}"
        daemon_reload: true
      ignore_errors: "{{ ansible_check_mode }}"