prometheus: add gauges for websocket connections

src/controllers/api/streaming.ts

@@ -5,6 +5,7 @@ import { z } from 'zod';
 import { type AppController } from '@/app.ts';
 import { Conf } from '@/config.ts';
 import { DittoDB } from '@/db/DittoDB.ts';
+import { streamingConnectionsGauge } from '@/metrics.ts';
 import { MuteListPolicy } from '@/policies/MuteListPolicy.ts';
 import { getFeedPubkeys } from '@/queries.ts';
 import { hydrateEvents } from '@/storages/hydrate.ts';
@@ -97,6 +98,8 @@ const streamingController: AppController = async (c) => {
   }
 
   socket.onopen = async () => {
+    streamingConnectionsGauge.inc();
+
     if (!stream) return;
     const topicFilter = await topicToFilter(stream, c.req.query(), pubkey);
 
@@ -120,6 +123,7 @@ const streamingController: AppController = async (c) => {
   };
 
   socket.onclose = () => {
+    streamingConnectionsGauge.dec();
     controller.abort();
   };
 

src/controllers/nostr/relay.ts

@@ -10,7 +10,7 @@ import {
 
 import { AppController } from '@/app.ts';
 import { relayInfoController } from '@/controllers/nostr/relay-info.ts';
-import { relayEventCounter, relayMessageCounter } from '@/metrics.ts';
+import { relayConnectionsGauge, relayEventCounter, relayMessageCounter } from '@/metrics.ts';
 import * as pipeline from '@/pipeline.ts';
 import { RelayError } from '@/RelayError.ts';
 import { Storages } from '@/storages.ts';
@@ -22,6 +22,10 @@ const FILTER_LIMIT = 100;
 function connectStream(socket: WebSocket) {
   const controllers = new Map<string, AbortController>();
 
+  socket.onopen = () => {
+    relayConnectionsGauge.inc();
+  };
+
   socket.onmessage = (e) => {
     const result = n.json().pipe(n.clientMsg()).safeParse(e.data);
     if (result.success) {
@@ -34,6 +38,8 @@ function connectStream(socket: WebSocket) {
   };
 
   socket.onclose = () => {
+    relayConnectionsGauge.dec();
+
     for (const controller of controllers.values()) {
       controller.abort();
     }

src/metrics.ts

@@ -1,4 +1,4 @@
-import { Counter } from 'prom-client';
+import { Counter, Gauge } from 'prom-client';
 
 export const httpRequestCounter = new Counter({
   name: 'http_requests_total',
@@ -6,6 +6,11 @@ export const httpRequestCounter = new Counter({
   labelNames: ['method'],
 });
 
+export const streamingConnectionsGauge = new Gauge({
+  name: 'streaming_connections',
+  help: 'Number of active connections to the streaming API',
+});
+
 export const fetchCounter = new Counter({
   name: 'fetch_total',
   help: 'Total number of fetch requests',
@@ -36,6 +41,11 @@ export const relayMessageCounter = new Counter({
   labelNames: ['verb'],
 });
 
+export const relayConnectionsGauge = new Gauge({
+  name: 'relay_connections',
+  help: 'Number of active connections to the relay',
+});
+
 export const dbQueryCounter = new Counter({
   name: 'db_query_total',
   help: 'Total number of database queries',