Use a keep-alive agent for got when sending to Hydro (github#28051)

Author: peterbe

lib/hydro.js

@@ -1,5 +1,8 @@
 import crypto from 'crypto'
+import { Agent } from 'https'
+
 import got from 'got'
+
 import statsd from '../lib/statsd.js'
 import FailBot from '../lib/failbot.js'
 
@@ -12,6 +15,21 @@ const TIME_OUT_TEXT = 'ms has passed since batch creation'
 // linger within the thread.
 const POST_TIMEOUT_MS = 3000
 
+let _agent
+function getHttpsAgent() {
+  if (!_agent) {
+    const agentOptions = {
+      // The most important option. This is false by default.
+      keepAlive: true,
+      // 32 because it's what's recommended here
+      // https://docs.microsoft.com/en-us/azure/app-service/app-service-web-nodejs-best-practices-and-troubleshoot-guide#my-node-application-is-making-excessive-outbound-calls
+      maxSockets: 32,
+    }
+    _agent = new Agent(agentOptions)
+  }
+  return _agent
+}
+
 export default class Hydro {
   constructor({ secret, endpoint } = {}) {
     this.secret = secret || process.env.HYDRO_SECRET
@@ -51,6 +69,8 @@ export default class Hydro {
     })
     const token = this.generatePayloadHmac(body)
 
+    const agent = getHttpsAgent()
+
     const doPost = () =>
       got(this.endpoint, {
         method: 'POST',
@@ -64,6 +84,11 @@ export default class Hydro {
         throwHttpErrors: false,
         // The default is no timeout.
         timeout: POST_TIMEOUT_MS,
+        agent: {
+          // Deliberately not setting up a `http` or `http2` agent
+          // because it won't be used for this particular `got` request.
+          https: agent,
+        },
       })
 
     const res = await statsd.asyncTimer(doPost, 'hydro.response_time')()