fix(v10/node-core): Register the Vercel SIGTERM listener once

packages/node-core/src/light/sdk.ts

@@ -29,6 +29,7 @@ import { defaultStackParser, getSentryRelease } from '../sdk/api';
 import { makeNodeTransport } from '../transports';
 import type { NodeClientOptions, NodeOptions } from '../types';
 import { getSpotlightConfig } from '../utils/spotlight';
+import { setupVercelSigtermFlush } from '../utils/vercel';
 import { setAsyncLocalStorageAsyncContextStrategy } from './asyncLocalStorageStrategy';
 import { LightNodeClient } from './client';
 import { httpIntegration } from './integrations/httpIntegration';
@@ -130,13 +131,8 @@ function _init(
 
   updateScopeFromEnvVariables();
 
-  // Ensure we flush events when vercel functions are ended
-  // See: https://vercel.com/docs/functions/functions-api-reference#sigterm-signal
   if (process.env.VERCEL) {
-    process.on('SIGTERM', async () => {
-      // We have 500ms for processing here, so we try to make sure to have enough time to send the events
-      await client.flush(200);
-    });
+    setupVercelSigtermFlush(client);
   }
 
   return client;

packages/node-core/src/sdk/index.ts

@@ -38,6 +38,7 @@ import { systemErrorIntegration } from '../integrations/systemError';
 import { makeNodeTransport } from '../transports';
 import type { NodeClientOptions, NodeOptions } from '../types';
 import { getSpotlightConfig } from '../utils/spotlight';
+import { setupVercelSigtermFlush } from '../utils/vercel';
 import { defaultStackParser, getSentryRelease } from './api';
 import { NodeClient } from './client';
 import { initializeEsmLoader } from './esmLoader';
@@ -147,13 +148,8 @@ function _init(
   enhanceDscWithOpenTelemetryRootSpanName(client);
   setupEventContextTrace(client);
 
-  // Ensure we flush events when vercel functions are ended
-  // See: https://vercel.com/docs/functions/functions-api-reference#sigterm-signal
   if (process.env.VERCEL) {
-    process.on('SIGTERM', async () => {
-      // We have 500ms for processing here, so we try to make sure to have enough time to send the events
-      await client.flush(200);
-    });
+    setupVercelSigtermFlush(client);
   }
 
   return client;

packages/node-core/src/utils/vercel.ts

@@ -0,0 +1,20 @@
+import type { Client } from '@sentry/core';
+
+// A repeated `init()` replaces the client, so a single listener flushes the latest one instead of adding one per init.
+let sigtermClient: Client | undefined;
+
+async function flushOnSigterm(): Promise<void> {
+  // We have 500ms for processing here, so we try to make sure to have enough time to send the events
+  await sigtermClient?.flush(200);
+}
+
+/**
+ * Ensure we flush events when vercel functions are ended.
+ * See: https://vercel.com/docs/functions/functions-api-reference#sigterm-signal
+ */
+export function setupVercelSigtermFlush(client: Client): void {
+  sigtermClient = client;
+  if (!process.listeners('SIGTERM').includes(flushOnSigterm)) {
+    process.on('SIGTERM', flushOnSigterm);
+  }
+}

packages/node-core/test/light/sdk.test.ts

@@ -62,6 +62,30 @@ describe('Light Mode | SDK', () => {
 
       expect(client?.getOptions().release).toBe('test-release@1.0.0');
     });
+
+    it('registers one SIGTERM handler on Vercel that flushes the latest client across repeated inits', () => {
+      const originalVercelEnv = process.env.VERCEL;
+      process.env.VERCEL = '1';
+
+      const baselineListeners = process.listeners('SIGTERM');
+
+      const firstClient = mockLightSdkInit();
+      const latestClient = mockLightSdkInit();
+      const firstFlushSpy = vi.spyOn(firstClient!, 'flush').mockResolvedValue(true);
+      const latestFlushSpy = vi.spyOn(latestClient!, 'flush').mockResolvedValue(true);
+
+      const postInitListeners = process.listeners('SIGTERM');
+      const addedListeners = postInitListeners.filter(l => !baselineListeners.includes(l));
+      expect(addedListeners).toHaveLength(1);
+
+      process.emit('SIGTERM');
+
+      expect(firstFlushSpy).not.toHaveBeenCalled();
+      expect(latestFlushSpy).toHaveBeenCalledWith(200);
+
+      process.off('SIGTERM', addedListeners[0] as any);
+      process.env.VERCEL = originalVercelEnv;
+    });
   });
 
   describe('initWithoutDefaultIntegrations', () => {

packages/node-core/test/sdk/init.test.ts

@@ -186,6 +186,30 @@ describe('init()', () => {
     process.env.VERCEL = originalVercelEnv;
   });
 
+  it('registers one SIGTERM handler on Vercel that flushes the latest client across repeated inits', () => {
+    const originalVercelEnv = process.env.VERCEL;
+    process.env.VERCEL = '1';
+
+    const baselineListeners = process.listeners('SIGTERM');
+
+    const firstClient = init({ dsn: PUBLIC_DSN, skipOpenTelemetrySetup: true });
+    const latestClient = init({ dsn: PUBLIC_DSN, skipOpenTelemetrySetup: true });
+    const firstFlushSpy = vi.spyOn(firstClient as NodeClient, 'flush').mockResolvedValue(true);
+    const latestFlushSpy = vi.spyOn(latestClient as NodeClient, 'flush').mockResolvedValue(true);
+
+    const postInitListeners = process.listeners('SIGTERM');
+    const addedListeners = postInitListeners.filter(l => !baselineListeners.includes(l));
+    expect(addedListeners).toHaveLength(1);
+
+    process.emit('SIGTERM');
+
+    expect(firstFlushSpy).not.toHaveBeenCalled();
+    expect(latestFlushSpy).toHaveBeenCalledWith(200);
+
+    process.off('SIGTERM', addedListeners[0] as any);
+    process.env.VERCEL = originalVercelEnv;
+  });
+
   it('does not register a SIGTERM handler when not running on Vercel', () => {
     const originalVercelEnv = process.env.VERCEL;
     delete process.env.VERCEL;