improv(tracing): allow to load exporter from environment #1676

packages/opentelemetry-core/src/utils/environment.ts

@@ -70,6 +70,7 @@ export type ENVIRONMENT = {
   OTEL_EXPORTER_ZIPKIN_ENDPOINT?: string;
   OTEL_LOG_LEVEL?: DiagLogLevel;
   OTEL_RESOURCE_ATTRIBUTES?: string;
+  OTEL_TRACES_EXPORTER?: string;
   OTEL_TRACES_SAMPLER_ARG?: string;
   OTEL_TRACES_SAMPLER?: string;
 } & ENVIRONMENT_NUMBERS &
@@ -105,6 +106,7 @@ export const DEFAULT_ENVIRONMENT: Required<ENVIRONMENT> = {
   OTEL_SPAN_ATTRIBUTE_COUNT_LIMIT: 128,
   OTEL_SPAN_EVENT_COUNT_LIMIT: 128,
   OTEL_SPAN_LINK_COUNT_LIMIT: 128,
+  OTEL_TRACES_EXPORTER: 'none',
   OTEL_TRACES_SAMPLER: TracesSamplerValues.ParentBasedAlwaysOn,
   OTEL_TRACES_SAMPLER_ARG: '',
 };

packages/opentelemetry-tracing/src/BasicTracerProvider.ts

@@ -32,11 +32,14 @@ import { Resource } from '@opentelemetry/resources';
 import { SpanProcessor, Tracer } from '.';
 import { DEFAULT_CONFIG } from './config';
 import { MultiSpanProcessor } from './MultiSpanProcessor';
-import { NoopSpanProcessor } from './NoopSpanProcessor';
+import { NoopSpanProcessor } from './export/NoopSpanProcessor';
 import { SDKRegistrationConfig, TracerConfig } from './types';
-const merge = require('lodash.merge');
+import merge = require('lodash.merge');
+import { SpanExporter } from './export/SpanExporter';
+import { BatchSpanProcessor } from './export/BatchSpanProcessor';
 
 export type PROPAGATOR_FACTORY = () => TextMapPropagator;
+export type EXPORTER_FACTORY = () => SpanExporter;
 
 /**
  * This class represents a basic tracer provider which platform libraries can extend
@@ -50,11 +53,16 @@ export class BasicTracerProvider implements TracerProvider {
     ['baggage', () => new HttpBaggagePropagator()],
   ]);
 
+  protected static readonly _registeredExporters = new Map<
+    string,
+    EXPORTER_FACTORY
+  >();
+
   private readonly _config: TracerConfig;
   private readonly _registeredSpanProcessors: SpanProcessor[] = [];
   private readonly _tracers: Map<string, Tracer> = new Map();
 
-  activeSpanProcessor: SpanProcessor = new NoopSpanProcessor();
+  activeSpanProcessor: SpanProcessor;
   readonly resource: Resource;
 
   constructor(config: TracerConfig = {}) {
@@ -64,6 +72,14 @@ export class BasicTracerProvider implements TracerProvider {
     this._config = Object.assign({}, mergedConfig, {
       resource: this.resource,
     });
+
+    const defaultExporter = this._buildExporterFromEnv();
+    if (defaultExporter !== undefined) {
+      const batchProcessor = new BatchSpanProcessor(defaultExporter);
+      this.activeSpanProcessor = batchProcessor;
+    } else {
+      this.activeSpanProcessor = new NoopSpanProcessor();
+    }
   }
 
   getTracer(name: string, version?: string): Tracer {
@@ -80,6 +96,18 @@ export class BasicTracerProvider implements TracerProvider {
    * @param spanProcessor the new SpanProcessor to be added.
    */
   addSpanProcessor(spanProcessor: SpanProcessor): void {
+    if (this._registeredSpanProcessors.length === 0) {
+      // since we might have enabled by default a batchProcessor, we disable it
+      // before adding the new one
+      this.activeSpanProcessor
+        .shutdown()
+        .catch(err =>
+          diag.error(
+            'Error while trying to shutdown current span processor',
+            err
+          )
+        );
+    }
     this._registeredSpanProcessors.push(spanProcessor);
     this.activeSpanProcessor = new MultiSpanProcessor(
       this._registeredSpanProcessors
@@ -120,6 +148,10 @@ export class BasicTracerProvider implements TracerProvider {
     return BasicTracerProvider._registeredPropagators.get(name)?.();
   }
 
+  protected _getSpanExporter(name: string): SpanExporter | undefined {
+    return BasicTracerProvider._registeredExporters.get(name)?.();
+  }
+
   protected _buildPropagatorFromEnv(): TextMapPropagator | undefined {
     // per spec, propagators from env must be deduplicated
     const uniquePropagatorNames = Array.from(
@@ -156,4 +188,16 @@ export class BasicTracerProvider implements TracerProvider {
       });
     }
   }
+
+  protected _buildExporterFromEnv(): SpanExporter | undefined {
+    const exporterName = getEnv().OTEL_TRACES_EXPORTER;
+    if (exporterName === 'none') return;
+    const exporter = this._getSpanExporter(exporterName);
+    if (!exporter) {
+      diag.warn(
+        `Exporter "${exporterName}" requested through environment variable is unavailable.`
+      );
+    }
+    return exporter;
+  }
 }

packages/opentelemetry-tracing/src/NoopSpanProcessor.ts → packages/opentelemetry-tracing/src/export/NoopSpanProcessor.ts

@@ -15,9 +15,9 @@
  */
 
 import { Context } from '@opentelemetry/api';
-import { ReadableSpan } from './export/ReadableSpan';
-import { Span } from './Span';
-import { SpanProcessor } from './SpanProcessor';
+import { ReadableSpan } from './ReadableSpan';
+import { Span } from '../Span';
+import { SpanProcessor } from '../SpanProcessor';
 
 /** No-op implementation of SpanProcessor */
 export class NoopSpanProcessor implements SpanProcessor {

packages/opentelemetry-tracing/src/index.ts

@@ -22,6 +22,7 @@ export * from './export/InMemorySpanExporter';
 export * from './export/ReadableSpan';
 export * from './export/SimpleSpanProcessor';
 export * from './export/SpanExporter';
+export * from './export/NoopSpanProcessor';
 export * from './Span';
 export * from './SpanProcessor';
 export * from './types';

packages/opentelemetry-tracing/test/BasicTracerProvider.test.ts

@@ -38,10 +38,13 @@ import {
 import { Resource } from '@opentelemetry/resources';
 import * as assert from 'assert';
 import * as sinon from 'sinon';
-import { BasicTracerProvider, Span } from '../src';
+import { BasicTracerProvider, NoopSpanProcessor, Span } from '../src';
 
 describe('BasicTracerProvider', () => {
   let removeEvent: Function | undefined;
+  const envSource = (typeof window !== 'undefined'
+    ? window
+    : process.env) as any;
 
   beforeEach(() => {
     context.disable();
@@ -120,13 +123,30 @@ describe('BasicTracerProvider', () => {
       const tracer = new BasicTracerProvider();
       assert.ok(tracer instanceof BasicTracerProvider);
     });
+
+    it('should use noop span processor by default', () => {
+      const tracer = new BasicTracerProvider();
+      assert.ok(tracer.activeSpanProcessor instanceof NoopSpanProcessor);
+    });
+
+    it('warns if there is no exporter registered with a given name', () => {
+      const warnStub = sinon.spy(diag, 'warn');
+
+      envSource.OTEL_TRACES_EXPORTER = 'missing-exporter';
+      const provider = new BasicTracerProvider({});
+      provider.register();
+
+      assert.ok(
+        warnStub.calledOnceWithExactly(
+          'Exporter "missing-exporter" requested through environment variable is unavailable.'
+        )
+      );
+      warnStub.restore();
+      envSource.OTEL_TRACES_EXPORTER = 'none';
+    });
   });
 
   describe('.register()', () => {
-    const envSource = (typeof window !== 'undefined'
-      ? window
-      : process.env) as any;
-
     describe('propagator', () => {
       class DummyPropagator implements TextMapPropagator {
         inject(