add environment variable to disable instrumentations completely (#3234)

package.json

@@ -19,7 +19,7 @@
     "test:appsec:ci": "nyc --no-clean --include \"packages/dd-trace/src/appsec/**/*.js\" --exclude \"packages/dd-trace/test/appsec/**/*.plugin.spec.js\" -- npm run test:appsec",
     "test:appsec:plugins": "mocha --colors --exit -r \"packages/dd-trace/test/setup/mocha.js\" \"packages/dd-trace/test/appsec/**/*.@($(echo $PLUGINS)).plugin.spec.js\"",
     "test:appsec:plugins:ci": "yarn services && nyc --no-clean --include \"packages/dd-trace/test/appsec/**/*.@($(echo $PLUGINS)).plugin.spec.js\" -- npm run test:appsec:plugins",
-    "test:trace:core": "tap packages/dd-trace/test/*.spec.js \"packages/dd-trace/test/{ci-visibility,encode,exporters,opentelemetry,opentracing,plugins,telemetry}/**/*.spec.js\"",
+    "test:trace:core": "tap packages/dd-trace/test/*.spec.js \"packages/dd-trace/test/{ci-visibility,config,encode,exporters,opentelemetry,opentracing,plugins,telemetry}/**/*.spec.js\"",
     "test:trace:core:ci": "npm run test:trace:core -- --coverage --nyc-arg=--include=\"packages/dd-trace/src/**/*.js\"",
     "test:instrumentations": "mocha --colors -r 'packages/dd-trace/test/setup/mocha.js' 'packages/datadog-instrumentations/test/**/*.spec.js'",
     "test:instrumentations:ci": "nyc --no-clean --include 'packages/datadog-instrumentations/src/**/*.js' -- npm run test:instrumentations",

packages/datadog-instrumentations/src/helpers/register.js

@@ -7,16 +7,23 @@ const Hook = require('./hook')
 const requirePackageJson = require('../../../dd-trace/src/require-package-json')
 const log = require('../../../dd-trace/src/log')
 
+const { DD_TRACE_DISABLED_INSTRUMENTATIONS = '' } = process.env
+
 const hooks = require('./hooks')
 const instrumentations = require('./instrumentations')
 const names = Object.keys(hooks)
 const pathSepExpr = new RegExp(`\\${path.sep}`, 'g')
+const disabledInstrumentations = new Set(
+  DD_TRACE_DISABLED_INSTRUMENTATIONS ? DD_TRACE_DISABLED_INSTRUMENTATIONS.split(',') : []
+)
 
 const loadChannel = channel('dd-trace:instrumentation:load')
 
 // TODO: make this more efficient
 
 for (const packageName of names) {
+  if (disabledInstrumentations.has(packageName)) continue
+
   Hook([packageName], (moduleExports, moduleName, moduleBaseDir, moduleVersion) => {
     moduleName = moduleName.replace(pathSepExpr, '/')
 

packages/dd-trace/test/config/disabled_instrumentations.spec.js

@@ -0,0 +1,18 @@
+'use strict'
+
+process.env.DD_TRACE_DISABLED_INSTRUMENTATIONS = 'express'
+
+require('../setup/tap')
+
+describe('config/disabled_instrumentations', () => {
+  it('should disable loading instrumentations completely', () => {
+    const handleBefore = require('express').application.handle
+    const tracer = require('../../../..')
+    const handleAfterImport = require('express').application.handle
+    tracer.init()
+    const handleAfterInit = require('express').application.handle
+
+    expect(handleBefore).to.equal(handleAfterImport)
+    expect(handleBefore).to.equal(handleAfterInit)
+  })
+})