ildkule/gatus: add healthcheck for postgresql

hosts/ildkule/services/monitoring/gatus/default.nix

@@ -5,6 +5,7 @@ in
 {
   imports = [
     ./minecraft-checker.nix
+    ./postgres-checker.nix
   ];
 
   services.gatus = {
@@ -133,6 +134,12 @@ in
             "[BODY].ok == true"
           ];
         })
+        (mkService "PostgreSQL" "http://localhost:1338" // {
+          conditions = [
+            "[STATUS] == 200"
+            "[BODY].ok == true"
+          ];
+        })
         (mkService "Email (SMTP)" "starttls://mail.pvv.ntnu.no:587")
         (mkService "Email (POP3)" "tls://mail.pvv.ntnu.no:995")
         (mkService "Email (IMAP)" "tls://mail.pvv.ntnu.no:993")

hosts/ildkule/services/monitoring/gatus/postgres-checker.nix

@@ -0,0 +1,79 @@
+{ config, pkgs, ... }:
+{
+  sops.secrets."keys/gatus/postgres" = {
+    restartUnits = [ "phh-gatus-postgres-checker.service" ];
+  };
+
+  sops.templates."gatus-postgres-checker.env" = {
+    restartUnits = [ "phh-gatus-postgres-checker.service" ];
+    content = ''
+      PGHOST=postgres.pvv.ntnu.no
+      PGPORT=5432
+      PGDATABASE=postgres
+      PGUSER=gatus_healthcheck
+      PGPASSWORD=${config.sops.placeholder."keys/gatus/postgres"}
+    '';
+  };
+
+  services.python-http-handlers."gatus-postgres-checker" = {
+    listenStreams = [ "127.0.0.1:1338" ];
+    libraries = with pkgs.python3Packages; [
+      psycopg2
+    ];
+    serviceConfig = {
+      EnvironmentFile = config.sops.templates."gatus-postgres-checker.env".path;
+    };
+    handler = ''
+      import os
+      import json
+      import psycopg2
+
+      class Handler(BaseHTTPRequestHandler):
+          def do_GET(self):
+              try:
+                  conn = psycopg2.connect(
+                      host=os.environ["PGHOST"],
+                      port=os.environ.get("PGPORT", "5432"),
+                      dbname=os.environ.get("PGDATABASE", "postgres"),
+                      user=os.environ["PGUSER"],
+                      password=os.environ["PGPASSWORD"],
+                      connect_timeout=5,
+                  )
+
+                  try:
+                      with conn.cursor() as cur:
+                          cur.execute("SELECT version();")
+                          (version,) = cur.fetchone()
+
+                          cur.execute("SELECT count(*) FROM pg_stat_activity;")
+                          (connections,) = cur.fetchone()
+
+                          cur.execute("SELECT count(*) FROM pg_database WHERE NOT datistemplate;")
+                          (databases,) = cur.fetchone()
+                  finally:
+                      conn.close()
+
+                  body = {
+                      "ok": True,
+                      "version": version,
+                      "connections": connections,
+                      "databases": databases,
+                  }
+                  data = json.dumps(body).encode()
+
+                  self.send_response(200)
+                  self.send_header("Content-Type", "application/json")
+                  self.send_header("Content-Length", str(len(data)))
+                  self.end_headers()
+                  self.wfile.write(data)
+
+              except Exception as e:
+                  data = json.dumps({"ok": False, "error": str(e)}).encode()
+                  self.send_response(500)
+                  self.send_header("Content-Type", "application/json")
+                  self.send_header("Content-Length", str(len(data)))
+                  self.end_headers()
+                  self.wfile.write(data)
+    '';
+  };
+}