feat: allow customizing OpenTelemetry infrastructure

Author: djMax

src/bootstrap.ts

@@ -4,6 +4,7 @@ import assert from 'node:assert';
 import { config } from 'dotenv';
 import { readPackageUp } from 'read-package-up';
 import type { NormalizedPackageJson } from 'read-package-up';
+import { NodeSDKConfiguration } from '@opentelemetry/sdk-node';
 
 import type {
   AnyServiceLocals,
@@ -64,6 +65,7 @@ async function getServiceDetails(argv: BootstrapArguments = {}) {
     rootDirectory: path.dirname(pkg.path),
     name: parts[parts.length - 1],
     version: pkg.packageJson.version,
+    customizer: (pkg.packageJson.config?.telemetry as { customizer?: string })?.customizer,
   };
 }
 
@@ -81,7 +83,7 @@ export async function bootstrap<
   SLocals extends AnyServiceLocals = ServiceLocals<ConfigurationSchema>,
   RLocals extends RequestLocals = RequestLocals,
 >(argv?: BootstrapArguments) {
-  const { main, rootDirectory, name, version } = await getServiceDetails(argv);
+  const { main, rootDirectory, name, version, customizer } = await getServiceDetails(argv);
 
   let entrypoint: string;
   let codepath: 'build' | 'dist' | 'src' = 'build';
@@ -104,12 +106,23 @@ export async function bootstrap<
 
   const absoluteEntrypoint = path.resolve(rootDirectory, entrypoint);
   if (argv?.telemetry) {
+    let otelCustomizer:
+      | ((options: Partial<NodeSDKConfiguration>) => Partial<NodeSDKConfiguration>)
+      | undefined = undefined;
+    if (customizer) {
+      // Customize OTEL with a dynamic import based on the codePath (so put it in src, generally)
+      otelCustomizer = (await import(`$(codePath}/${customizer}`)).NodeSDKConfiguration;
+      if (typeof otelCustomizer === 'object') {
+        otelCustomizer = (v) => ({ ...v, ...(otelCustomizer as Partial<NodeSDKConfiguration>) });
+      }
+    }
     return startWithTelemetry<SLocals, RLocals>({
       name,
       rootDirectory,
       service: absoluteEntrypoint,
       codepath,
       version,
+      customizer: otelCustomizer,
     });
   }
 

src/telemetry/index.ts

@@ -72,7 +72,14 @@ let telemetrySdk: opentelemetry.NodeSDK | undefined;
  * In addition, since we have to load it right away before configuration
  * is available, we can't use configuration to decide anything.
  */
-export async function startGlobalTelemetry(serviceName: string) {
+export async function startGlobalTelemetry(
+  serviceName: string,
+  customizer?:
+    | ((
+        options: Partial<opentelemetry.NodeSDKConfiguration>,
+      ) => Partial<opentelemetry.NodeSDKConfiguration>)
+    | undefined,
+) {
   if (!prometheusExporter) {
     const { metrics, logs, NodeSDK } = opentelemetry;
 
@@ -90,7 +97,7 @@ export async function startGlobalTelemetry(serviceName: string) {
     prometheusExporter = new PrometheusExporter({ preventServerStart: true });
     const instrumentations = getAutoInstrumentations();
     const logExporter = getLogExporter();
-    telemetrySdk = new NodeSDK({
+    const options: Partial<opentelemetry.NodeSDKConfiguration> = {
       serviceName,
       autoDetectResources: false,
       resource,
@@ -111,7 +118,8 @@ export async function startGlobalTelemetry(serviceName: string) {
           },
         },
       ],
-    });
+    };
+    telemetrySdk = new NodeSDK(customizer ? customizer(options) : options);
     telemetrySdk.start();
   }
 }
@@ -130,7 +138,7 @@ export async function startWithTelemetry<
   SLocals extends AnyServiceLocals = ServiceLocals<ConfigurationSchema>,
   RLocals extends RequestLocals = RequestLocals,
 >(options: DelayLoadServiceStartOptions) {
-  await startGlobalTelemetry(options.name);
+  await startGlobalTelemetry(options.name, options.customizer);
 
   // eslint-disable-next-line import/no-unresolved, @typescript-eslint/no-var-requires
   const { startApp, listen } = (await import('../express-app/app.js')) as {

src/types.ts

@@ -6,6 +6,7 @@ import type { Request, Response } from 'express';
 import type { Application } from 'express-serve-static-core';
 import type { middleware } from 'express-openapi-validator';
 import type { Meter } from '@opentelemetry/api';
+import type { NodeSDKConfiguration } from '@opentelemetry/sdk-node';
 import { ShortstopHandler } from '@sesamecare-oss/confit';
 
 import { ConfigurationSchema } from './config/schema.js';
@@ -144,6 +145,9 @@ export interface ServiceStartOptions<
 
 export interface DelayLoadServiceStartOptions extends Omit<ServiceStartOptions, 'service'> {
   service: string;
+  customizer?:
+    | ((options: Partial<NodeSDKConfiguration>) => Partial<NodeSDKConfiguration>)
+    | undefined;
 }
 
 // Handled by service.configure