fix: avoid IPv4 vs IPv6 ambiguity in default 'serverUrl' by using '12…

…7.0.0.1' rather than 'localhost'

Starting in node v17 the defaults for DNS resolution order was
changed (nodejs/node#39987) such that
`dns.lookup()` no longer sorted IPv4 addresses first. This impacts
usage of the *default* APM Server URL (the `serverUrl` config var),
'http://localhost:8200', when using node >=17 because the APM server
only binds to the IPv4 address by default
(elastic/apm-server#1405).

Fixes: #3045

examples/trace-http-request.js

@@ -17,6 +17,8 @@ const apm = require('../').start({ // elastic-apm-node
   useElasticTraceparentHeader: false
 })
 
+console.log('XXX ', apm._conf.serverUrl)
+
 const http = require('http')
 
 function makeARequest (url, opts, cb) {

lib/agent.js

@@ -198,15 +198,6 @@ Agent.prototype.setSpanOutcome = function (outcome) {
 Agent.prototype._config = function (opts) {
   this._conf = config.createConfig(opts, this.logger)
   this.logger = this._conf.logger
-
-  const { host, port, protocol } = this._conf.serverUrl
-    ? parsers.parseUrl(this._conf.serverUrl)
-    : { host: 'localhost:8200', port: '8200' }
-
-  this._conf.serverHost = host
-  this._conf.serverPort = port === ''
-    ? (protocol === 'https:' ? 443 : 80)
-    : parseInt(port, 10)
 }
 
 Agent.prototype.isStarted = function () {
@@ -225,18 +216,27 @@ Agent.prototype.start = function (opts) {
     this.addFilter(require('./filters/http-headers'))
   }
 
+  // Check cases where we do *not* start.
   if (!this._conf.active) {
     this.logger.debug('Elastic APM agent disabled (`active` is false)')
     return this
   } else if (!this._conf.serviceName) {
     this.logger.error('Elastic APM is incorrectly configured: Missing serviceName (APM will be disabled)')
     this._conf.active = false
     return this
-  } else if (!(this._conf.serverPort >= 1 && this._conf.serverPort <= 65535)) {
+  }
+  // Sanity check the port from `serverUrl`.
+  const parsedUrl = parsers.parseUrl(this._conf.serverUrl)
+  const serverPort = (parsedUrl.port
+    ? Number(parsedUrl.port)
+    : (parsedUrl.protocol === 'https:' ? 443 : 80))
+  if (!(serverPort >= 1 && serverPort <= 65535)) {
     this.logger.error('Elastic APM is incorrectly configured: serverUrl "%s" contains an invalid port! (allowed: 1-65535)', this._conf.serverUrl)
     this._conf.active = false
     return this
-  } else if (this._conf.logLevel === 'trace') {
+  }
+
+  if (this._conf.logLevel === 'trace') {
     var stackObj = {}
     Error.captureStackTrace(stackObj)
 

lib/config.js

@@ -90,6 +90,7 @@ var DEFAULTS = {
   ],
   serviceNodeName: undefined,
   serverTimeout: '30s',
+  serverUrl: 'http://127.0.0.1:8200',
   sourceLinesErrorAppFrames: 5,
   sourceLinesErrorLibraryFrames: 5,
   sourceLinesSpanAppFrames: 0,
@@ -541,8 +542,7 @@ class Config {
     const REDACT_FIELDS = {
       apiKey: true,
       secretToken: true,
-      serverUrl: true,
-      serverHost: true
+      serverUrl: true
     }
     const NICE_REGEXPS_FIELDS = {
       ignoreUrlRegExp: true,