add prometheus metrics (fixes #47)

package-lock.json

@@ -7453,6 +7453,11 @@
         "node": ">=8"
       }
     },
+    "node_modules/bintrees": {
+      "version": "1.0.2",
+      "resolved": "https://registry.npmjs.org/bintrees/-/bintrees-1.0.2.tgz",
+      "integrity": "sha512-VOMgTMwjAaUG580SXn3LacVgjurrbMme7ZZNYGSSV7mmtY6QQRh0Eg3pwIcntQ77DErK1L0NxkbetjcoXzVwKw=="
+    },
     "node_modules/bl": {
       "version": "4.1.0",
       "resolved": "https://registry.npmjs.org/bl/-/bl-4.1.0.tgz",
@@ -12428,6 +12433,18 @@
         "node": ">=0.4.0"
       }
     },
+    "node_modules/prom-client": {
+      "version": "15.1.2",
+      "resolved": "https://registry.npmjs.org/prom-client/-/prom-client-15.1.2.tgz",
+      "integrity": "sha512-on3h1iXb04QFLLThrmVYg1SChBQ9N1c+nKAjebBjokBqipddH3uxmOUcEkTnzmJ8Jh/5TSUnUqS40i2QB2dJHQ==",
+      "dependencies": {
+        "@opentelemetry/api": "^1.4.0",
+        "tdigest": "^0.1.1"
+      },
+      "engines": {
+        "node": "^16 || ^18 || >=20"
+      }
+    },
     "node_modules/prompts": {
       "version": "2.4.2",
       "resolved": "https://registry.npmjs.org/prompts/-/prompts-2.4.2.tgz",
@@ -14215,6 +14232,14 @@
         "node": ">=6"
       }
     },
+    "node_modules/tdigest": {
+      "version": "0.1.2",
+      "resolved": "https://registry.npmjs.org/tdigest/-/tdigest-0.1.2.tgz",
+      "integrity": "sha512-+G0LLgjjo9BZX2MfdvPfH+MKLCrxlXSYec5DaPYP1fe6Iyhf0/fSmJ0bFiZ1F8BT6cGXl2LpltQptzjXKWEkKA==",
+      "dependencies": {
+        "bintrees": "1.0.2"
+      }
+    },
     "node_modules/temp-dir": {
       "version": "2.0.0",
       "resolved": "https://registry.npmjs.org/temp-dir/-/temp-dir-2.0.0.tgz",
@@ -16298,6 +16323,7 @@
         "express-session": "^1.17.3",
         "openid-client": "^5.6.5",
         "prisma-dbml-generator": "^0.12.0",
+        "prom-client": "^15.1.2",
         "rate-limit-redis": "^4.2.0",
         "redis": "^4.6.12",
         "socket.io": "^4.7.2",

packages/server/package.json

@@ -39,6 +39,7 @@
     "express-session": "^1.17.3",
     "openid-client": "^5.6.5",
     "prisma-dbml-generator": "^0.12.0",
+    "prom-client": "^15.1.2",
     "rate-limit-redis": "^4.2.0",
     "redis": "^4.6.12",
     "socket.io": "^4.7.2",

packages/server/src/index.ts

@@ -28,6 +28,18 @@ if (!process.env.SESSION_SECRET) {
   process.exit(1);
 }
 
+if (!process.env.NODE_APP_INSTANCE) {
+  Logger.warn(
+    "NODE_APP_INSTANCE is not defined, metrics will not include process label"
+  );
+}
+
+if (!process.env.PROMETHEUS_TOKEN) {
+  Logger.warn(
+    "PROMETHEUS_TOKEN is not defined, /metrics will not be accessable"
+  );
+}
+
 if (!process.env.REDIS_HOST) {
   Logger.error("REDIS_HOST is not defined");
   process.exit(1);

packages/server/src/lib/Canvas.ts

@@ -141,6 +141,23 @@ class Canvas {
     return await this.canvasToRedis();
   }
 
+  /**
+   * Get if a pixel is maybe empty
+   * @param x
+   * @param y
+   * @returns
+   */
+  async isPixelEmpty(x: number, y: number) {
+    const redis = await Redis.getClient();
+    const pixelColor = await redis.get(Redis.key("pixelColor", x, y));
+
+    if (pixelColor === null) {
+      return true;
+    }
+
+    return pixelColor === "transparent";
+  }
+
   async getPixel(x: number, y: number) {
     return (
       await prisma.pixel.findMany({

packages/server/src/lib/Express.ts

@@ -9,6 +9,7 @@ import APIRoutes_client from "../api/client";
 import APIRoutes_admin from "../api/admin";
 import { Logger } from "./Logger";
 import bodyParser from "body-parser";
+import { handleMetricsEndpoint } from "./Prometheus";
 
 export const session = expressSession({
   secret: process.env.SESSION_SECRET,
@@ -93,6 +94,7 @@ export class ExpressServer {
     this.app.use(bodyParser.json());
     this.app.use("/api", APIRoutes_client);
     this.app.use("/api/admin", APIRoutes_admin);
+    this.app.use("/metrics", handleMetricsEndpoint);
 
     this.httpServer.listen(parseInt(process.env.PORT), () => {
       Logger.info("Listening on :" + process.env.PORT);

packages/server/src/lib/Prometheus.ts

@@ -0,0 +1,113 @@
+import client, { register } from "prom-client";
+import { prisma } from "./prisma";
+import e from "express";
+import { SocketServer } from "./SocketServer";
+import Canvas from "./Canvas";
+import { Redis } from "./redis";
+
+client.collectDefaultMetrics({
+  labels: process.env.NODE_APP_INSTANCE
+    ? {
+        NODE_APP_INSTANCE: process.env.NODE_APP_INSTANCE,
+      }
+    : {},
+});
+
+export const PixelCount = new client.Gauge({
+  name: "pixel_count",
+  help: "total pixel count",
+
+  async collect() {
+    this.set(await prisma.pixel.count());
+  },
+});
+
+export const UserCount = new client.Gauge({
+  name: "user_count",
+  help: "total user count",
+
+  async collect() {
+    this.set(await prisma.user.count());
+  },
+});
+
+export const OnlineUsers = new client.Gauge({
+  name: "connected_count",
+  help: "total connected sockets",
+
+  async collect() {
+    this.set((await SocketServer.instance.io.fetchSockets()).length);
+  },
+});
+
+/**
+ * Rough estimate of empty pixels
+ */
+export const EmptyPixels = new client.Gauge({
+  name: "empty_pixels",
+  help: "total number of empty pixels",
+
+  async collect() {
+    let queries: Promise<boolean>[] = [];
+
+    for (let x = 0; x < Canvas.getCanvasConfig().size[0]; x++) {
+      for (let y = 0; y < Canvas.getCanvasConfig().size[1]; y++) {
+        queries.push(Canvas.isPixelEmpty(x, y));
+      }
+    }
+
+    let count = 0;
+
+    const allSettled = await Promise.allSettled(queries);
+    for (const settle of allSettled) {
+      if (settle.status === "fulfilled") {
+        count += Number(settle.value);
+      } else {
+        count++;
+      }
+    }
+
+    this.set(count);
+  },
+});
+
+export const TotalPixels = new client.Gauge({
+  name: "total_pixels",
+  help: "total number of pixels the canvas allows",
+
+  async collect() {
+    const [width, height] = Canvas.getCanvasConfig().size;
+
+    this.set(width * height);
+  },
+});
+
+export const UniqueInstances = new client.Gauge({
+  name: "instance_count",
+  help: "total number of unique instances",
+
+  async collect() {
+    this.set(await prisma.instance.count());
+  },
+});
+
+export const handleMetricsEndpoint = async (
+  req: e.Request,
+  res: e.Response
+) => {
+  if (!process.env.PROMETHEUS_TOKEN) {
+    res.status(500);
+    res.send("PROMETHEUS_TOKEN is not set.");
+    return;
+  }
+
+  if (req.headers.authorization !== "Bearer " + process.env.PROMETHEUS_TOKEN) {
+    res.status(401);
+    res.send("Invalid bearer token");
+    return;
+  }
+
+  res.setHeader("Content-Type", register.contentType);
+  res.send(await register.metrics());
+  res.end();
+};

packages/server/src/types.ts

@@ -19,12 +19,16 @@ declare global {
   namespace NodeJS {
     interface ProcessEnv {
       NODE_ENV: "development" | "production";
+      NODE_APP_INSTANCE?: string;
       PORT: string;
       LOG_LEVEL?: string;
       SESSION_SECRET: string;
+
+      PROMETHEUS_TOKEN?: string;
+
       REDIS_HOST: string;
-      REDIS_SESSION_PREFIX: string;
-      REDIS_RATELIMIT_PREFIX: string;
+      REDIS_SESSION_PREFIX?: string;
+      REDIS_RATELIMIT_PREFIX?: string;
 
       /**
        * hostname that is used in the callback