NestJS OpenTelemetry (OTEL)

Description

OpenTelemetry module for Nest.

Why

Setting up observability metrics with nestjs requires multiple libraries and patterns. OpenTelemetry has support for multiple exporters and types of metrics such as Prometheus Metrics.

Observability

Please read this comprehensive whitepaper if that's your first time working with metrics, tracing, and logs.

Examples

A full working examples are available. This includes a nestjs application fully integrated with prometheus, grafana, loki and tempo:

• nestjs-otel-prom-grafana-tempo

Installation

npm i nestjs-otel @opentelemetry/sdk-node --save

Setup

Some peers dependencies are required when some configurations are enabled.

@opentelemetry/exporter-prometheus

1. Create tracing file (tracing.ts):

import {
  CompositePropagator,
  W3CTraceContextPropagator,
  W3CBaggagePropagator,
} from '@opentelemetry/core';
import { BatchSpanProcessor } from '@opentelemetry/sdk-trace-base';
import { JaegerExporter } from '@opentelemetry/exporter-jaeger';
import { getNodeAutoInstrumentations } from '@opentelemetry/auto-instrumentations-node';
import { JaegerPropagator } from '@opentelemetry/propagator-jaeger';
import { B3Propagator } from '@opentelemetry/propagator-b3';
import { PrometheusExporter } from '@opentelemetry/exporter-prometheus';
import { NodeSDK } from '@opentelemetry/sdk-node';
import { AsyncLocalStorageContextManager } from '@opentelemetry/context-async-hooks';
import * as process from 'process';

const otelSDK = new NodeSDK({
  metricReader: new PrometheusExporter({
    port: 8081,
  }),
  spanProcessor: new BatchSpanProcessor(new JaegerExporter()),
  contextManager: new AsyncLocalStorageContextManager(),
  textMapPropagator: new CompositePropagator({
    propagators: [
      new JaegerPropagator(),
      new W3CTraceContextPropagator(),
      new W3CBaggagePropagator(),
      new B3Propagator(),
    ],
  }),
  instrumentations: [getNodeAutoInstrumentations()],
});

export default otelSDK;

// You can also use the shutdown method to gracefully shut down the SDK before process shutdown
// or on some operating system signal.
process.on('SIGTERM', () => {
  otelSDK
    .shutdown()
    .then(
      () => console.log('SDK shut down successfully'),
      err => console.log('Error shutting down SDK', err)
    )
    .finally(() => process.exit(0));
});

2. Import the metric file and start otel node SDK:

import otelSDK from './tracing';
import { NestFactory } from '@nestjs/core';
import { AppModule } from './app.module';
import { Logger } from 'nestjs-pino';

async function bootstrap() {
  // Start SDK before nestjs factory create
  await otelSDK.start();

  const app = await NestFactory.create(AppModule);
  app.useLogger(app.get(Logger));
  await app.listen(3000);
}
bootstrap();

3. Configure nest-otel:

3.1. With forRoot:

const OpenTelemetryModuleConfig = OpenTelemetryModule.forRoot({
  metrics: {
    hostMetrics: true, // Includes Host Metrics
    apiMetrics: { // @deprecated - will be removed in 8.0 - you should start using the semcov from opentelemetry metrics instead
      enable: true, // Includes api metrics
      defaultAttributes: {
        // You can set default labels for api metrics
        custom: 'label',
      },
      ignoreRoutes: ['/favicon.ico'], // You can ignore specific routes (See https://docs.nestjs.com/middleware#excluding-routes for options)
      ignoreUndefinedRoutes: false, //Records metrics for all URLs, even undefined ones
      prefix: 'my_prefix', // Add a custom prefix to all API metrics
    },
  },
});

@Module({
  imports: [OpenTelemetryModuleConfig],
})
export class AppModule {}

3.2. With forRootAsync:

OpenTelemetryModule.forRootAsync({
  useClass: OtelConfigService
});

import { Injectable, Logger } from '@nestjs/common'
import { ConfigService } from '@nestjs/config'
import { OpenTelemetryOptionsFactory, OpenTelemetryModuleOptions } from 'nestjs-otel';

@Injectable()
export class OtelConfigService implements OpenTelemetryOptionsFactory {
  private readonly logger = new Logger(OtelConfigService.name)

  constructor(private configService: ConfigService) {}

  createOpenTelemetryOptions(): Promise<OpenTelemetryModuleOptions> | OpenTelemetryModuleOptions {
    const { hostMetrics, apiMetrics } = this.configService.get('otel')

    return {
      metrics: {
        hostMetrics: hostMetrics.enabled,
        apiMetrics: {
          enable: apiMetrics.enabled,
        },
      },
    };
  }
}

Span Decorator

If you need, you can define a custom Tracing Span for a method. It works async or sync.

Span optionally takes one or both of the following parameters:

• name - explicit name of the span; if omitted, it is derived as <class-name>.<method-name>.
• options - SpanOptions to customize the span options.

You can also supply a function as the options argument. It will be called with the decorated method's arguments, so you can dynamically customize the span options.

import { Span } from 'nestjs-otel';

export class BooksService {

  // span.name == 'CRITICAL_SECTION'
  @Span('CRITICAL_SECTION')
  async getBooks() {
      return [`Harry Potter and the Philosopher's Stone`];
  }

  // span.name == 'BooksService.getBooksAgain'
  @Span()
  async getBooksAgain() {
      return [`Harry Potter and the Philosopher's Stone`];
  }

  // explicitly set span options
  @Span('getBook', { kind: SpanKind.SERVER })
  async getBook(id: number) {
    // ...
  }

  // options are set dynamically based on the id parameter
  @Span('getBook', (id) => ({ attributes: { bookId: id } }))
  async getBookAgain(id: number) {
    // ...
  }

  // same as above, but span name is omitted and inferred automatically
  @Span((id) => ({ attributes: { bookId: id } }))
  async getBookOnceMore(id: number) {
    // ...
  }
}

Tracing Service

In case you need to access native span methods for special logics in the method block:

import { TraceService } from 'nestjs-otel';

@Injectable()
export class BookService {
  constructor(private readonly traceService: TraceService) {}

  @Span()
  async getBooks() {
    const currentSpan = this.traceService.getSpan(); // --> retrives current span, comes from http or @Span
    await this.doSomething();
    currentSpan.addEvent('event 1');
    currentSpan.end(); // current span end

    const span = this.traceService.startSpan('sub_span'); // start new span
    span.setAttributes({ userId: 1 });
    await this.doSomethingElse();
    span.end(); // new span ends
    return [`Harry Potter and the Philosopher's Stone`];
  }
}

Metric Service

OpenTelemetry Metrics allow a user to collect data and export it to metrics backend like Prometheus.

import { MetricService } from 'nestjs-otel';
import { Counter } from '@opentelemetry/api';

@Injectable()
export class BookService {
  private customMetricCounter: Counter;

  constructor(private readonly metricService: MetricService) {
    this.customMetricCounter = this.metricService.getCounter('custom_counter', {
      description: 'Description for counter',
    });
  }

  async getBooks() {
    this.customMetricCounter.add(1);
    return [`Harry Potter and the Philosopher's Stone`];
  }
}

Metric Decorators

Metric Class Instances

If you want to count how many instance of a specific class has been created:

@OtelInstanceCounter() // It will generate a counter called: app_MyClass_instances_total.
export class MyClass {}

Metric Class Method

If you want to increment a counter on each call of a specific method:

@Injectable()
export class MyService {
  @OtelMethodCounter()
  doSomething() {}
}
@Controller()
export class AppController {
  @Get()
  @OtelMethodCounter() // It will generate `app_AppController_doSomething_calls_total` counter.
  doSomething() {
    // do your stuff
  }
}

Metric Param Decorator

You have the following decorators:

• @OtelCounter()
• @OtelUpDownCounter()
• @OtelHistogram()
• @OtelGauge()
• @OtelObservableGauge()
• @OtelObservableCounter()
• @OtelObservableUpDownCounter()

Example of usage:

import { OtelCounter } from 'nestjs-otel';
import { Counter } from '@opentelemetry/api';

@Controller()
export class AppController {
  @Get('/home')
  home(
    @OtelCounter('app_counter_1_inc', { description: 'counter 1 description' }) counter1: Counter
  ) {
    counter1.add(1);
  }
}

API Metrics with Middleware

@deprecated - this will be removed in 8.0 - you should start using the semcov from opentelemetry metrics instead

| Impl | Otel Metric | Prometheus Metric | Description | Metric Type | | ---- | -------------------------------- | --------------------------------------- | ----------------------------------------- | ----------- | | ✅ | http.server.request.count | http_server_request_count_total | Total number of HTTP requests. | Counter | | ✅ | http.server.response.count | http_server_response_count_total | Total number of HTTP responses. | Counter | | ✅ | http.server.abort.count | http_server_abort_count_total | Total number of data transfers aborted. | Counter | | ✅ | http.server.duration | http_server_duration | The duration of the inbound HTTP request. | Histogram | | ✅ | http.server.request.size | http_server_request_size | Size of incoming bytes. | Histogram | | ✅ | http.server.response.size | http_server_response_size | Size of outgoing bytes. | Histogram | | ✅ | http.server.response.success.count | http_server_response_success_count_total | Total number of all successful responses. | Counter | | ✅ | http.server.response.error.count | http_server_response_error_count_total | Total number of server error responses. | Counter | | ✅ | http.client.request.error.count | http_client_request_error_count_total | Total number of client error requests. | Counter |

Prometheus Metrics

When metricExporter is defined in otel SDK with a PrometheusExporterit will start a new process on port 8081 (default port) and metrics will be available at http://localhost:8081/metrics.

Using with a logger

Pino with instrumentation

This approach uses otel instrumentation to automatically inject spanId and traceId.

import { PinoInstrumentation } from '@opentelemetry/instrumentation-pino';

const otelSDK = new NodeSDK({
  instrumentations: [new PinoInstrumentation()],
});

Pino with custom formatter

This approach uses the global trace context for injecting SpanId and traceId as a property of your structured log.

import Pino, { Logger } from 'pino';
import { LoggerOptions } from 'pino';
import { trace, context } from '@opentelemetry/api';

export const loggerOptions: LoggerOptions = {
  formatters: {
    log(object) {
      const span = trace.getSpan(context.active());
      if (!span) return { ...object };
      const { spanId, traceId } = trace.getSpan(context.active())?.spanContext();
      return { ...object, spanId, traceId };
    },
  },
};

export const logger: Logger = Pino(loggerOptions);

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