feat: Drop unsampled transactions when connected to APM Server 8.0+ (#2546)

This updates to an elastic-apm-http-client that calls the APM Server
Information API on creation to get the APM Server version.

Closes: #2455

Author: trentm

CHANGELOG.asciidoc

@@ -37,6 +37,8 @@ Notes:
 [float]
 ===== Features
 
+* Drop unsampled transactions when sending to APM Server v8.0+. ({issues}2455[#2455])
+
 * The default <<service-name, `serviceName`>> string (when it is not configured
   and cannot be inferred from a "package.json" file) has been changed from
   "nodejs_service" to "unknown-nodejs-service". This is a standardized pattern

lib/config.js

@@ -925,9 +925,10 @@ function getBaseClientConfig (conf, agent) {
     time: conf.apiRequestTime * 1000,
     maxQueueSize: conf.maxQueueSize,
 
-    // Debugging
+    // Debugging/testing options
     logger: clientLogger,
     payloadLogFile: conf.payloadLogFile,
+    apmServerVersion: conf.apmServerVersion,
 
     // Container conf
     containerId: conf.containerId,

lib/instrumentation/index.js

@@ -281,6 +281,11 @@ Instrumentation.prototype.addEndedTransaction = function (transaction) {
     return
   }
 
+  // https://github.com/elastic/apm/blob/main/specs/agents/tracing-sampling.md#non-sampled-transactions
+  if (!transaction.sampled && !agent._transport.supportsKeepingUnsampledTransaction()) {
+    return
+  }
+
   var payload = agent._transactionFilters.process(transaction._encode())
   if (!payload) {
     agent.logger.debug('transaction ignored by filter %o', { trans: transaction.id, trace: transaction.traceId })

lib/noop-transport.js

@@ -43,6 +43,10 @@ class NoopTransport {
     }
   }
 
+  supportsKeepingUnsampledTransaction () {
+    return true
+  }
+
   // Inherited from Writable, called in agent.js.
   destroy () {}
 }

package.json

@@ -88,7 +88,7 @@
     "basic-auth": "^2.0.1",
     "cookie": "^0.4.0",
     "core-util-is": "^1.0.2",
-    "elastic-apm-http-client": "^10.3.0",
+    "elastic-apm-http-client": "^10.4.0",
     "end-of-stream": "^1.4.4",
     "error-callsites": "^2.0.4",
     "error-stack-parser": "^2.0.6",

test/_capturing_transport.js

@@ -77,6 +77,10 @@ class CapturingTransport {
     }
   }
 
+  supportsKeepingUnsampledTransaction () {
+    return true
+  }
+
   // Inherited from Writable, called in agent.js.
   destroy () {}
 }

test/_mock_apm_server.js

@@ -1,7 +1,7 @@
 // A mock APM server to use in tests.
 //
 // Usage:
-//    const server = new MockAPMServer()
+//    const server = new MockAPMServer(opts)
 //    server.start(function (serverUrl) {
 //      // Test code using `serverUrl`...
 //      // - Events received on the intake API will be on `server.events`.
@@ -16,9 +16,14 @@ const { URL } = require('url')
 const zlib = require('zlib')
 
 class MockAPMServer {
-  constructor () {
+  // - @param {Object} opts
+  //    - {String} opts.apmServerVersion - The version to report in the
+  //      "GET /" response body. Defaults to "8.0.0".
+  constructor (opts) {
+    opts = opts || {}
     this.clear()
     this.serverUrl = null // set in .start()
+    this.apmServerVersion = opts.apmServerVersion || '8.0.0'
     this._http = http.createServer(this._onRequest.bind(this))
   }
 
@@ -43,7 +48,15 @@ class MockAPMServer {
 
     instream.on('end', () => {
       let resBody = ''
-      if (parsedUrl.pathname === '/config/v1/agents') {
+      if (req.method === 'GET' && parsedUrl.pathname === '/') {
+        // https://www.elastic.co/guide/en/apm/server/current/server-info.html#server-info-endpoint
+        res.writeHead(200)
+        resBody = JSON.stringify({
+          build_date: '2021-09-16T02:05:39Z',
+          build_sha: 'a183f675ecd03fca4a897cbe85fda3511bc3ca43',
+          version: this.apmServerVersion
+        })
+      } else if (parsedUrl.pathname === '/config/v1/agents') {
         // Central config mocking.
         res.writeHead(200)
         resBody = '{}'

test/_mock_http_client.js

@@ -54,6 +54,9 @@ module.exports = function (expected, done) {
     },
     flush (cb) {
       if (cb) process.nextTick(cb)
+    },
+    supportsKeepingUnsampledTransaction () {
+      return true
     }
   }
 

test/_mock_http_client_states.js

@@ -35,6 +35,9 @@ module.exports = function (expectations = [], done) {
     },
     flush (cb) {
       if (cb) process.nextTick(cb)
+    },
+    supportsKeepingUnsampledTransaction () {
+      return true
     }
   }
 }

test/agent.test.js

@@ -553,7 +553,12 @@ test('filters', function (t) {
       filterAgentOpts = Object.assign(
         {},
         agentOpts,
-        { serverUrl }
+        {
+          serverUrl,
+          // Ensure the APM client's `GET /` requests do not get in the way of
+          // the test asserts below.
+          apmServerVersion: '8.0.0'
+        }
       )
       t.end()
     })