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,