feat: DataDog metrics (#2228)

* wip

* chore: Change event names, add additional events

* fix: Not counting connect events

server/main.js

@@ -9,6 +9,7 @@ import { Document, Collection, View } from "./models";
 import policy from "./policies";
 import { client, subscriber } from "./redis";
 import { getUserForJWT } from "./utils/jwt";
+import * as metrics from "./utils/metrics";
 import { checkMigrations } from "./utils/startup";
 
 const server = http.createServer(app.callback());
@@ -38,6 +39,16 @@ io.of("/").adapter.on("error", (err) => {
   }
 });
 
+io.on("connection", (socket) => {
+  metrics.increment("websockets.connected");
+  metrics.gauge("websockets.count", socket.client.conn.server.clientsCount);
+
+  socket.on("disconnect", () => {
+    metrics.increment("websockets.disconnected");
+    metrics.gauge("websockets.count", socket.client.conn.server.clientsCount);
+  });
+});
+
 SocketAuth(io, {
   authenticate: async (socket, data, callback) => {
     const { token } = data;
@@ -83,7 +94,9 @@ SocketAuth(io, {
         }).findByPk(event.collectionId);
 
         if (can(user, "read", collection)) {
-          socket.join(`collection-${event.collectionId}`);
+          socket.join(`collection-${event.collectionId}`, () => {
+            metrics.increment("websockets.collections.join");
+          });
         }
       }
 
@@ -103,6 +116,8 @@ SocketAuth(io, {
           );
 
           socket.join(room, () => {
+            metrics.increment("websockets.documents.join");
+
             // let everyone else in the room know that a new user joined
             io.to(room).emit("user.join", {
               userId: user.id,
@@ -146,11 +161,15 @@ SocketAuth(io, {
     // allow the client to request to leave rooms
     socket.on("leave", (event) => {
       if (event.collectionId) {
-        socket.leave(`collection-${event.collectionId}`);
+        socket.leave(`collection-${event.collectionId}`, () => {
+          metrics.increment("websockets.collections.leave");
+        });
       }
       if (event.documentId) {
         const room = `document-${event.documentId}`;
         socket.leave(room, () => {
+          metrics.increment("websockets.documents.leave");
+
           io.to(room).emit("user.leave", {
             userId: user.id,
             documentId: event.documentId,
@@ -174,6 +193,8 @@ SocketAuth(io, {
     });
 
     socket.on("presence", async (event) => {
+      metrics.increment("websockets.presence");
+
       const room = `document-${event.documentId}`;
 
       if (event.documentId && socket.rooms[room]) {

server/utils/metrics.js

@@ -0,0 +1,26 @@
+// @flow
+import metrics from "datadog-metrics";
+
+if (process.env.DD_API_KEY) {
+  metrics.init({
+    apiKey: process.env.DD_API_KEY,
+    prefix: "outline.",
+    defaultTags: [`env:${process.env.DD_ENV || process.env.NODE_ENV}`],
+  });
+}
+
+export function gauge(key: string, value: number): void {
+  if (!process.env.DD_API_KEY) {
+    return;
+  }
+
+  return metrics.gauge(key, value);
+}
+
+export function increment(key: string, tags?: { [string]: string }): void {
+  if (!process.env.DD_API_KEY) {
+    return;
+  }
+
+  return metrics.increment(key, tags);
+}