feat(tracer): implement process discovery feature (#5782)

* feat(tracer): implement process discovery feature

Resolves [APMAPI-1071]

Author: dmehala

integration-tests/startup.spec.js

@@ -9,6 +9,8 @@ const {
 const path = require('path')
 const { assert } = require('chai')
 const semver = require('semver')
+const { inspect } = require('util')
+const fs = require('fs')
 
 const execArgvs = [
   {
@@ -72,6 +74,39 @@ execArgvs.forEach(({ execArgv, skip }) => {
         })
       })
 
+      it('saves tracer configuration on disk', async () => {
+        if (process.platform !== 'linux') {
+          return
+        }
+
+        proc = await spawnProc(startupTestFile, {
+          cwd,
+          execArgv,
+          env: {
+            AGENT_PORT: agent.port
+          }
+        })
+
+        const containsDatadogMemfd = (fds) => {
+          for (const fd of fds) {
+            try {
+              const fdName = fs.readlinkSync(`/proc/${proc.pid}/fd/${fd}`)
+              if (fdName.includes('datadog-tracer-info-')) {
+                return true
+              }
+            } catch {}
+          }
+          return false
+        }
+
+        const fds = fs.readdirSync(`/proc/${proc.pid}/fd`)
+
+        assert(
+          containsDatadogMemfd(fds),
+          `FDs ${inspect(fds)} of PID ${proc.pid} did not contain the datadog tracer configuration in memfd`
+        )
+      })
+
       it('works for options.url', async () => {
         proc = await spawnProc(startupTestFile, {
           cwd,

packages/dd-trace/src/tracer.js

@@ -24,6 +24,17 @@ class DatadogTracer extends Tracer {
     this._scope = new Scope()
     setStartupLogConfig(config)
     flushStartupLogs(log)
+
+    if (!config._isInServerlessEnvironment()) {
+      const storeConfig = require('./tracer_metadata')
+      // Keep a reference to the handle, to keep the memfd alive in memory.
+      // It is read by the service discovery feature.
+      const metadata = storeConfig(config)
+      if (metadata === undefined) {
+        log.warn('Could not store tracer configuration for service discovery')
+      }
+      this._inmem_cfg = metadata
+    }
   }
 
   configure (config) {

packages/dd-trace/src/tracer_metadata.js

@@ -0,0 +1,25 @@
+'use strict'
+
+// Load binding first to not import other modules if it throws
+const libdatadog = require('@datadog/libdatadog')
+const tracerVersion = require('../../../version').VERSION
+
+function storeConfig (config) {
+  const processDiscovery = libdatadog.maybeLoad('process-discovery')
+  if (processDiscovery === undefined) {
+    return
+  }
+
+  const metadata = new processDiscovery.TracerMetadata(
+    config.tags['runtime-id'],
+    tracerVersion,
+    config.hostname,
+    config.server || null,
+    config.env || null,
+    config.version || null
+  )
+
+  return processDiscovery.storeMetadata(metadata)
+}
+
+module.exports = storeConfig

version.js

@@ -3,10 +3,12 @@
 /* eslint-disable no-var */
 /* eslint-disable unicorn/prefer-number-properties */
 
-var ddMatches = require('./package.json').version.match(/^(\d+)\.(\d+)\.(\d+)/)
+var version = require('./package.json').version
+var ddMatches = version.match(/^(\d+)\.(\d+)\.(\d+)/)
 var nodeMatches = process.versions.node.match(/^(\d+)\.(\d+)\.(\d+)/)
 
 module.exports = {
+  VERSION: version,
   DD_MAJOR: parseInt(ddMatches[1]),
   DD_MINOR: parseInt(ddMatches[2]),
   DD_PATCH: parseInt(ddMatches[3]),