feat: make prometheus config preventServerStart optional (#1375)

* feat: make prometheus config startServer mandatory

* fix: degrade log level on startServer is false

* fix: remove the log on not starting server

* fix: callbacks shall be called asynchronously unconditionally

* fixup!: update the options with `preventServerStart`

packages/opentelemetry-exporter-prometheus/src/PrometheusExporter.ts

@@ -26,7 +26,6 @@ import { PrometheusLabelsBatcher } from './PrometheusLabelsBatcher';
 export class PrometheusExporter implements MetricExporter {
   static readonly DEFAULT_OPTIONS = {
     port: 9464,
-    startServer: false,
     endpoint: '/metrics',
     prefix: '',
   };
@@ -59,7 +58,7 @@ export class PrometheusExporter implements MetricExporter {
       config.endpoint || PrometheusExporter.DEFAULT_OPTIONS.endpoint
     ).replace(/^([^/])/, '/$1');
 
-    if (config.startServer || PrometheusExporter.DEFAULT_OPTIONS.startServer) {
+    if (config.preventServerStart !== true) {
       this.startServer().then(callback);
     } else if (callback) {
       callback();

packages/opentelemetry-exporter-prometheus/src/export/types.ts

@@ -43,10 +43,10 @@ export interface ExporterConfig {
   port?: number;
 
   /**
-   * Define if the Prometheus exporter server will be started
+   * Prevent the Prometheus exporter server from starting
    * @default false
    */
-  startServer?: boolean;
+  preventServerStart?: boolean;
 
   /** Standard logging interface */
   logger?: api.Logger;