Add serving metrics for Prometheus

Co-authored-by: TheEssem <smswessem@gmail.com>

.env.example

@@ -44,6 +44,8 @@ OUTPUT=
 TEMPDIR=
 # Put temporary image web server domain
 TMP_DOMAIN=
+# Port for serving metrics. Metrics served are compatible with Prometheus.
+METRICS=
 
 # Set this to true if you're using PM2 to manage the bot
 PMTWO=false

shard.js

@@ -21,6 +21,7 @@ const misc = require("./utils/misc.js");
 // generate help page
 const helpGenerator =
   process.env.OUTPUT !== "" ? require("./utils/help.js") : null;
+const http = require("http");
 
 class Shard extends Base {
   constructor(bot) {
@@ -68,6 +69,40 @@ class Shard extends Base {
       logger.log("info", "The help docs have been generated.");
     }
 
+    if (process.env.METRICS !== "") {
+      logger.log("YES");
+      const httpServer = http.createServer((req, res) => {
+        if (req.method !== "GET") {
+          res.statusCode = 405;
+          return res.end("GET only");
+        }
+        res.write(`# HELP connected_workers Number of workers connected
+# TYPE connected_workers guage
+connected_workers ${image.connections.length}
+# HELP running_jobs Number of running jobs on this worker
+# TYPE running_jobs guage
+# HELP queued_jobs Number of queued jobs on this worker
+# TYPE queued_jobs guage
+# HELP max_jobs Number of max allowed jobs on this worker
+# TYPE max_jobs guage
+`);
+        image.getStatus().then((servers) => {
+          for (const [i, w] of servers.entries()) {
+            res.write(`running_jobs{worker="${i}} ${w.runningJobs}\n`);
+            res.write(`queued_jobs{worker="${i}} ${w.queued}\n`);
+            res.write(`max_jobs{worker="${i}} ${w.max}\n`);
+          }
+          res.end();
+        }).catch(e => {
+          res.statusCode = 500;
+          return res.end(e);
+        });
+      });
+      httpServer.listen(process.env.METRICS, () => {
+        logger.log("info", `Serving metrics at ${process.env.METRICS}`);
+      });
+    }
+
     // handle process stop
     process.on("SIGINT", () => {
       logger.log("warn", "SIGINT detected, shutting down...");