prometheus: add blackbox exporter

roles/prometheus/templates/prometheus.yml.j2

@@ -26,6 +26,35 @@ scrape_configs:
     static_configs:
       - targets: ["localhost:9090"]
 
+  - job_name: "blackbox"
+    static_configs:
+      - targets: ["blackbox_exporter:9115"]
+
+{% if prometheus_ping_hosts | length > 0 %}
+  - job_name: "icmp"
+    metrics_path: "/probe"
+    params:
+      module: ["icmp"]
+    static_configs:
+      - targets:
+{% for host in prometheus_ping_hosts %}
+          - "{{ host.name }}::{{ host.type | default('monitored') }}"
+{% endfor %}
+    relabel_configs:
+      - source_labels: [__address__]
+        regex: '(.+)::(.+)'
+        target_label: __param_target
+        replacement: '${1}'
+      - source_labels: [__address__]
+        regex: '(.+)::(.+)'
+        target_label: host_type
+        replacement: '${2}'
+      - source_labels: [__param_target]
+        target_label: instance
+      - target_label: __address__
+        replacement: blackbox_exporter:9115
+{%- endif %}
+
 {% if prometheus_hcloud_enabled %}
   - job_name: hcloud
     hetzner_sd_configs: