gatherer: add watchdog triggered by wget

gatherer/src/http_server.rs

@@ -11,6 +11,7 @@ use axum::{
     Router, middleware::{Next, self}, body::Body,
 };
 use axum_extra::routing::SpaRouter;
+use cave::systemd;
 use crate::{
     html_template::HtmlTemplate,
     RequestFactory,
@@ -58,6 +59,10 @@ impl TrendsPage {
     async fn generate(language: Option<String>, mux: Mux) -> Self {
         let (results, languages) = mux.request(language.clone()).await;
 
+        // redis queries done, data is ready for rendering, means the
+        // service is very much alive:
+        systemd::watchdog();
+
         TrendsPage {
             language,
             languages,

nixos-module.nix

@@ -118,6 +118,7 @@ in
       serviceConfig = {
         ExecStart = "${pkgs.caveman-gatherer}/bin/caveman-gatherer ${gathererConfigFile}";
         Type = "notify";
+        WatchdogSec = 90;
         Restart = "always";
         RestartSec = 10;
         DynamicUser = true;
@@ -136,5 +137,23 @@ in
         WorkingDirectory = "${pkgs.caveman-gatherer}/share/caveman/gatherer";
       };
     };
+
+    systemd.timers.caveman-gatherer-probe = lib.mkIf cfg.gatherer.enable {
+      wantedBy = [ "timers.target" ];
+      timerConfig.OnCalendar = "minutely";
+    };
+    systemd.services.caveman-gatherer-probe = lib.mkIf cfg.gatherer.enable {
+      requires = [ "caveman-gatherer.service" ];
+      serviceConfig = {
+        Type = "oneshot";
+        User = "caveman-gatherer-probe";
+        DynamicUser = true;
+        ProtectSystem = "full";
+      };
+      path = with pkgs; [ wget ];
+      script = ''
+        wget -O /dev/null --user-agent=caveman-gatherer-probe 127.0.0.1:${toString gathererSettings.listen_port}/
+      '';
+    };
   };
 }