feat: allow manual instrumentation with instrument: false (#1114)

Fixes #858

docs/configuration.asciidoc

@@ -119,7 +119,7 @@ You must use the query bar to filter for a specific environment in versions prio
 * *Default:* `true`
 * *Env:* `ELASTIC_APM_INSTRUMENT`
 
-A boolean specifying if the agent should collect performance metrics for the app.
+A boolean specifying if the agent should automatically apply instrumentation to supported modules when they are loaded.
 
 Note that both `active` and `instrument` needs to be `true` for instrumentation to be running.
 

lib/instrumentation/index.js

@@ -130,9 +130,7 @@ Instrumentation.prototype.clearPatches = function (modules) {
 Instrumentation.modules = Object.freeze(MODULES)
 
 Instrumentation.prototype.start = function () {
-  if (!this._agent._conf.instrument) return
   if (this._started) return
-
   this._started = true
 
   if (this._agent._conf.asyncHooks && semver.gte(process.version, '8.2.0')) {
@@ -164,7 +162,7 @@ Instrumentation.prototype._startHook = function () {
   this._agent.logger.debug('adding hook to Node.js module loader')
 
   this._hook = hook(this._patches.keys, function (exports, name, basedir) {
-    var enabled = !disabled.has(name)
+    var enabled = self._agent._conf.instrument && !disabled.has(name)
     var pkg, version
 
     if (basedir) {

test/_mock_http_client.js

@@ -50,7 +50,7 @@ module.exports = function (expected, done) {
     if (timer) clearTimeout(timer)
     timer = setTimeout(function () {
       done(client._writes)
-    }, 100)
+    }, 200)
   }
 }
 

test/config.js

@@ -804,6 +804,29 @@ test('globalLabels should be received by transport', function (t) {
   })
 })
 
+test('instrument: false allows manual instrumentation', function (t) {
+  var trans
+  var opts = {
+    metricsInterval: 0,
+    instrument: false
+  }
+
+  var server = APMServer(opts, { expect: 'transaction' })
+    .on('listening', function () {
+      trans = this.agent.startTransaction('trans')
+      trans.end()
+      this.agent.flush()
+    })
+    .on('data-transaction', (data) => {
+      assertEncodedTransaction(t, trans, data)
+      t.end()
+    })
+
+  t.on('end', function () {
+    server.destroy()
+  })
+})
+
 function assertEncodedTransaction (t, trans, result) {
   t.comment('transaction')
   t.equal(result.id, trans.id, 'id matches')