fix(config): extract relevant env vars from pm2_env JSON before tracer init

eslint.config.mjs

@@ -690,7 +690,9 @@ export default [
         // The following are false positives that are supported in Node.js 0.8.0
         ignores: [
           'JSON',
+          'JSON.parse',
           'JSON.stringify',
+          'Object.keys',
           'parseInt',
           'String',
         ],
@@ -700,6 +702,7 @@ export default [
         ignores: [
           'array-prototype-indexof',
           'json',
+          'object-keys',
         ],
       }],
       'no-var': 'off', // Only supported in Node.js 6+

init.js

@@ -1,5 +1,23 @@
 'use strict'
 
+// In PM2 cluster mode, per-app env vars arrive as a `pm2_env`
+// JSON string after --require has already run so we extract them
+// manually if present.
+var pm2EnvStr = process.env.pm2_env
+if (typeof pm2EnvStr === 'string') {
+  try {
+    var pm2Config = JSON.parse(pm2EnvStr)
+    var pm2Keys = Object.keys(pm2Config)
+    for (var i = 0; i < pm2Keys.length; i++) {
+      var k = pm2Keys[i]
+      var v = pm2Config[k]
+      if (v != null) {
+        process.env[k] = String(v)
+      }
+    }
+  } catch (e) {}
+}
+
 var guard = require('./packages/dd-trace/src/guardrails')
 
 module.exports = guard(function () {

integration-tests/init.spec.js

@@ -272,6 +272,56 @@ describe('init.js', () => {
 
   testInjectionScenarios('require', 'init.js', false)
   testRuntimeVersionChecks('require', 'init.js')
+
+  describe('PM2 cluster mode', () => {
+    useEnv({ NODE_OPTIONS: '--require dd-trace/init' })
+
+    afterEach(() => {
+      delete process.env.pm2_env
+    })
+
+    function checkEnv (expectedValues) {
+      return testFile('init/pm2-env.js', out => {
+        const env = JSON.parse(out.trim())
+        for (const [key, value] of Object.entries(expectedValues)) {
+          assert.strictEqual(env[key], value, `expected env.${key} to equal ${value}`)
+        }
+      }, [], '')
+    }
+
+    it('applies all env vars from pm2_env blob to process.env', () => {
+      process.env.pm2_env = JSON.stringify({ DD_SERVICE: 'pm2-svc', DD_ENV: 'pm2-env', MY_APP_VAR: 'hello' })
+      return checkEnv({ DD_SERVICE: 'pm2-svc', DD_ENV: 'pm2-env', MY_APP_VAR: 'hello' })
+    })
+
+    it('coerces non-string values to strings', () => {
+      process.env.pm2_env = JSON.stringify({ DD_TRACE_SAMPLE_RATE: 0.5 })
+      return checkEnv({ DD_TRACE_SAMPLE_RATE: '0.5' })
+    })
+
+    it('skips keys with null values', () => {
+      process.env.pm2_env = JSON.stringify({ DD_SERVICE: null })
+      return checkEnv({ DD_SERVICE: undefined })
+    })
+
+    it('does not crash on malformed pm2_env JSON', () => {
+      process.env.pm2_env = 'not-valid-json'
+      return checkEnv({ DD_SERVICE: undefined })
+    })
+
+    it('does nothing when pm2_env is absent', () => {
+      return checkEnv({ DD_SERVICE: undefined })
+    })
+
+    describe('when env vars are already set', () => {
+      useEnv({ DD_SERVICE: 'original-service', MY_APP_VAR: 'original' })
+
+      it('overwrites existing env vars with pm2_env values', () => {
+        process.env.pm2_env = JSON.stringify({ DD_SERVICE: 'pm2-service', MY_APP_VAR: 'pm2-value' })
+        return checkEnv({ DD_SERVICE: 'pm2-service', MY_APP_VAR: 'pm2-value' })
+      })
+    })
+  })
 })
 
 // ESM is not supportable prior to Node.js 14.13.1 on the 14.x line,

integration-tests/init/pm2-env.js

@@ -0,0 +1,10 @@
+'use strict'
+
+// eslint-disable-next-line no-console
+console.log(JSON.stringify({
+  DD_SERVICE: process.env.DD_SERVICE,
+  DD_ENV: process.env.DD_ENV,
+  DD_TRACE_SAMPLE_RATE: process.env.DD_TRACE_SAMPLE_RATE,
+  MY_APP_VAR: process.env.MY_APP_VAR,
+}))
+process.exit()