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/config.alloy.j2

@@ -0,0 +1,78 @@
+// Managed by Ansible (role monitoring_agent): logs of {{ inventory_hostname }} to Loki.
+
+discovery.docker "containers" {
+  host = "unix:///var/run/docker.sock"
+}
+
+discovery.relabel "containers" {
+  targets = discovery.docker.containers.targets
+
+  rule {
+    source_labels = ["__meta_docker_container_name"]
+    regex         = "/(.*)"
+    target_label  = "container"
+  }
+  rule {
+    source_labels = ["__meta_docker_container_label_com_docker_compose_project"]
+    target_label  = "compose_project"
+  }
+  rule {
+    source_labels = ["__meta_docker_container_label_com_docker_compose_service"]
+    target_label  = "compose_service"
+  }
+}
+
+loki.source.docker "containers" {
+  host          = "unix:///var/run/docker.sock"
+  targets       = discovery.docker.containers.targets
+  relabel_rules = discovery.relabel.containers.rules
+  labels        = { job = "docker" }
+  forward_to    = [loki.process.containers.receiver]
+}
+
+loki.process "containers" {
+  // CI job containers are many, short-lived and noisy: the runner logs suffice
+  stage.match {
+    selector = "{container=~\"FORGEJO-ACTIONS-TASK-.*\"}"
+    action   = "drop"
+  }
+  forward_to = [loki.write.default.receiver]
+}
+
+loki.relabel "journal" {
+  forward_to = []
+
+  rule {
+    source_labels = ["__journal__systemd_unit"]
+    target_label  = "unit"
+  }
+  rule {
+    source_labels = ["__journal_priority_keyword"]
+    target_label  = "level"
+  }
+}
+
+loki.source.journal "journal" {
+  max_age       = "12h"
+  relabel_rules = loki.relabel.journal.rules
+  labels        = { job = "journal" }
+  forward_to    = [loki.write.default.receiver]
+}
+{% if inventory_hostname == 'asxpio-ops' %}
+
+local.file_match "traefik" {
+  path_targets = [{ "__path__" = "/traefik-logs/access.log", job = "traefik-access" }]
+}
+
+loki.source.file "traefik" {
+  targets    = local.file_match.traefik.targets
+  forward_to = [loki.write.default.receiver]
+}
+{% endif %}
+
+loki.write "default" {
+  endpoint {
+    url = "http://{{ asxpio_ops_vpc_ip }}:{{ monitoring_loki_port }}/loki/api/v1/push"
+  }
+  external_labels = { host = "{{ inventory_hostname }}" }
+}