ansible: monitoring with Prometheus, Loki and Grafana

Nothing watched the servers: tonight's asxpio crash loop was found by
hand. On asxpio-ops, Prometheus (30 days), Loki (14 days) and Grafana
at gf.asxp.io (WireGuard only), with blackbox_exporter probing every
service from outside and postgres_exporter. On both hosts node_exporter
and cAdvisor on the VPC address, and Alloy shipping container logs, the
journal and Traefik's access log to Loki over the VPC.

Traefik and Forgejo expose their metrics; restic and the bucket replica
record their last success for node_exporter. Dashboards: an overview as
home, plus hosts, containers, Traefik, probes, Postgres and logs.
Alerts by email to me@asxp.io: host or service down, certificate under
14 days, disk or memory nearly full, a container restart-looping,
Postgres down, backup or replica stale.

Assisted-by: Claude:opus-5-5

ansible/roles/monitoring_agent/templates/docker-compose.yml.j2

@@ -0,0 +1,66 @@
+# Managed by Ansible (role monitoring_agent).
+services:
+  node-exporter:
+    image: prom/node-exporter:{{ monitoring_node_exporter_version }}
+    container_name: node-exporter
+    command:
+      - --path.rootfs=/host
+      - --web.listen-address={{ vpc_ip }}:{{ monitoring_node_exporter_port }}
+      - --collector.textfile.directory=/textfile
+      - --collector.filesystem.mount-points-exclude=^/(dev|proc|run|sys|var/lib/docker/.+)($|/)
+    network_mode: host
+    pid: host
+    volumes:
+      - /:/host:ro,rslave
+      - {{ monitoring_textfile_dir }}:/textfile:ro
+    restart: unless-stopped
+    mem_limit: 64m
+
+  cadvisor:
+    image: ghcr.io/google/cadvisor:{{ monitoring_cadvisor_version }}
+    container_name: cadvisor
+    command:
+      - --listen_ip={{ vpc_ip }}
+      - --port={{ monitoring_cadvisor_port }}
+      - --docker_only=true
+      - --housekeeping_interval=30s
+      - --store_container_labels=false
+      - --whitelisted_container_labels=com.docker.compose.project,com.docker.compose.service
+      - --disable_metrics=percpu,sched,tcp,udp,hugetlb,referenced_memory,cpu_topology,resctrl,advtcp,process
+    network_mode: host
+    privileged: true
+    devices:
+      - /dev/kmsg
+    volumes:
+      - /:/rootfs:ro
+      - /var/run:/var/run:ro
+      - /sys:/sys:ro
+      - /var/lib/docker/:/var/lib/docker:ro
+      - /dev/disk/:/dev/disk:ro
+    restart: unless-stopped
+    mem_limit: 192m
+
+  alloy:
+    image: grafana/alloy:{{ monitoring_alloy_version }}
+    container_name: alloy
+    command:
+      - run
+      - --server.http.listen-addr={{ vpc_ip }}:12345
+      - --storage.path=/var/lib/alloy/data
+      - /etc/alloy/config.alloy
+    network_mode: host
+    volumes:
+      - ./config.alloy:/etc/alloy/config.alloy:ro
+      - /var/run/docker.sock:/var/run/docker.sock:ro
+      - /var/log/journal:/var/log/journal:ro
+      - /run/log/journal:/run/log/journal:ro
+      - /etc/machine-id:/etc/machine-id:ro
+{% if inventory_hostname == 'asxpio-ops' %}
+      - /opt/traefik/logs:/traefik-logs:ro
+{% endif %}
+      - alloy-data:/var/lib/alloy/data
+    restart: unless-stopped
+    mem_limit: 256m
+
+volumes:
+  alloy-data: