Add VictoriaLogs for centralized journald across all hosts

control runs VictoriaLogs (:9428, 30d, mesh-scoped) with a matching
Grafana datasource. Each host ships journald via systemd's own
journald.upload to the /insert/journald endpoint -- no extra agent.
control uploads over loopback so its logs survive a mesh outage; ns1
and ns2 push over the mesh.

TODO.md

@@ -57,7 +57,13 @@ ns1/ns2: SOA + DNSKEY succeed on both servers over v4 and v6.
 - [ ] A secondary nameserver on a different provider/network so a single-provider
       outage doesn't take all authoritative DNS down (architectural — new machine)
 
-## 5. Centralized logs
+## 5. Centralized logs (done — pending deploy)
 
-- [ ] VictoriaLogs on control to grep journald across all three hosts, pairing
+VictoriaLogs on control (`:9428`, 30d retention, mesh-scoped) in
+`modules/monitoring/server.nix`, plus a VictoriaLogs Grafana datasource. All
+three hosts ship journald with systemd's own `services.journald.upload` to the
+`/insert/journald` endpoint (`modules/monitoring/exporters.nix`) — no extra
+agent. control uploads over loopback; ns1/ns2 over the mesh.
+
+- [x] VictoriaLogs on control to grep journald across all three hosts, pairing
       with the existing VictoriaMetrics setup

docs/src/monitoring.md

@@ -42,6 +42,25 @@ Dashboards are provisioned from `modules/monitoring/dashboards/` (any JSON file
 there is picked up):
 
 - **CNX DNS** (`dns.json`) — firing alerts, per-nameserver SOA serials, zone
-  expiry countdowns, query/response rates, and host CPU/memory/disk/load.
+  expiry countdowns, query/response rates, host CPU/memory/disk/load, and the
+  outside-in DNS probes.
 - **CNX Backups** (`backups.json`) — borgbackup job health, time since the last
   run, and per-job state. See [Backups](./backups.md).
+
+## Logs
+
+**VictoriaLogs** on `control` (`:9428`), 30-day retention
+(`modules/monitoring/server.nix`). All three hosts ship journald to it via
+systemd's own `services.journald.upload` → the `/insert/journald` endpoint
+(`modules/monitoring/exporters.nix`); no extra agent. `control` uploads over
+loopback so its logs survive a mesh outage, `ns1`/`ns2` push over the mesh, and
+9428 is firewall-scoped to the mesh like everything else.
+
+Query logs from Grafana via the provisioned **VictoriaLogs** datasource (Explore
+view, LogsQL), or directly in the built-in UI at `http://[control]:9428/select/vmui`.
+Logs are tagged with `_HOSTNAME` and `_SYSTEMD_UNIT`, so to follow one service
+across hosts:
+
+```
+_SYSTEMD_UNIT:"knot.service"
+```

modules/monitoring/exporters.nix

@@ -1,5 +1,6 @@
-# Metric exporters, imported by every machine. Host metrics everywhere; Knot DNS
-# metrics on the nameservers. Everything is reachable only over the ZeroTier mesh
+# Per-host observability agents, imported by every machine. Host metrics
+# everywhere; Knot DNS metrics on the nameservers; journald shipped to
+# VictoriaLogs on control. Everything is reachable only over the ZeroTier mesh
 # (see the firewall rule at the bottom); the public side is already closed by the
 # Hetzner cloud firewall.
 {
@@ -86,6 +87,22 @@ in
     ];
   };
 
+  # Ship journald to VictoriaLogs on control (services.victorialogs in
+  # server.nix). control uploads to loopback so its own logs survive a mesh
+  # outage; ns1/ns2 push over the mesh to control's ZeroTier address.
+  services.journald.upload = {
+    enable = true;
+    settings.Upload.URL =
+      let
+        dest =
+          if config.networking.hostName == "control" then
+            "127.0.0.1:9428"
+          else
+            "[${mesh.hosts.control}]:9428";
+      in
+      "http://${dest}/insert/journald";
+  };
+
   # Scrape ports reachable only from the ZeroTier mesh.
   networking.firewall.extraInputRules = ''
     ip6 saddr ${mesh.subnet} tcp dport { ${lib.concatMapStringsSep ", " toString ports} } accept

modules/monitoring/server.nix

@@ -12,6 +12,7 @@ let
   mesh = import ../mesh-hosts.nix { inherit config lib; };
   probes = import ./blackbox-probes.nix { inherit lib; };
   vmPort = 8428;
+  logsPort = 9428;
   grafanaPort = 3000;
   controlV6 = mesh.hosts.control;
 
@@ -60,6 +61,17 @@ in
     };
   };
 
+  # Centralized logs: VictoriaLogs ingests journald from all three hosts, each
+  # of which runs systemd-journal-upload against /insert/journald (exporters.nix).
+  # Binds all interfaces because ns1/ns2 push over the mesh; the firewall rule at
+  # the bottom scopes 9428 to the mesh subnet and the Hetzner firewall closes the
+  # public side. Retention is set via extraOptions (no dedicated NixOS option).
+  services.victorialogs = {
+    enable = true;
+    listenAddress = ":${toString logsPort}";
+    extraOptions = [ "-retentionPeriod=30d" ];
+  };
+
   # Admin password generated once and stored as a clan secret. Retrieve with:
   #   clan vars get control grafana-admin/password
   clan.core.vars.generators.grafana-admin = {
@@ -76,6 +88,9 @@ in
 
   services.grafana = {
     enable = true;
+    # VictoriaLogs datasource plugin so journald is greppable from Grafana,
+    # alongside the metrics datasource.
+    declarativePlugins = [ pkgs.grafanaPlugins.victoriametrics-logs-datasource ];
     settings = {
       server = {
         http_addr = "::";
@@ -102,6 +117,13 @@ in
             url = "http://127.0.0.1:${toString vmPort}";
             isDefault = true;
           }
+          {
+            name = "VictoriaLogs";
+            type = "victoriametrics-logs-datasource";
+            uid = "victorialogs";
+            access = "proxy";
+            url = "http://127.0.0.1:${toString logsPort}";
+          }
         ];
       };
       dashboards.settings = {
@@ -117,8 +139,9 @@ in
     };
   };
 
-  # Grafana reachable only from the ZeroTier mesh (admin laptops + servers).
+  # Grafana (admin laptops + servers) and VictoriaLogs ingestion (ns1/ns2 push
+  # journald over the mesh) reachable only from the ZeroTier mesh.
   networking.firewall.extraInputRules = ''
-    ip6 saddr ${mesh.subnet} tcp dport ${toString grafanaPort} accept
+    ip6 saddr ${mesh.subnet} tcp dport { ${toString grafanaPort}, ${toString logsPort} } accept
   '';
 }