How Does the Firebase Admin SDK Determine the Project ID When Not Specified?

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I'm debugging an issue where writes from my Node.js script to the local Firestore emulator aren't visible in the emulator UI, and the data retrieved by the script doesn't match what the UI shows.

I suspect the Node.js script is connecting to a different Firestore instance locally, possibly due to an implicit project ID. The emulator is started with firebase emulators:start --only functions,firestore and displays data at http://127.0.0.1:4000/firestore/default/data/ added by emulated functions, with the home page confirming the project ID. However, my script doesn't seem to use that same project ID.

Below is my initialization code:

JAVASCRIPT
import { initializeApp } from 'firebase-admin/app';
import { getFirestore } from 'firebase-admin/firestore';

for (const envVar of [
  'FIREBASE_CONFIG',  // env var listed at https://firebase.google.com/docs/admin/setup#initialize-sdk
  'GOOGLE_APPLICATION_CREDENTIALS',  // env var listed at https://firebase.google.com/docs/admin/setup#initialize_the_sdk_in_non-google_environments
  'GOOGLE_CLOUD_PROJECT', 'GCLOUD_PROJECT'  // observed access while debugging with Deno
])
  console.log(`${envVar}:`, process.env[envVar]);  // all undefined

// Connect to the emulator per https://firebase.google.com/docs/emulator-suite/connect_firestore#admin_sdks or https://cloud.google.com/firestore/docs/emulator#server_client_libraries
process.env['FIRESTORE_EMULATOR_HOST'] = '127.0.0.1:8080';
// Initialize Cloud Firestore per https://firebase.google.com/docs/firestore/quickstart#initialize -> Node.js -> Initialize on your own server
initializeApp();
const db = getFirestore();

My question is: How does Firebase/Firestore determine the project ID when none is provided via parameters, environment variables, or configuration files? Any insights or workarounds to ensure both my script and the emulator UI reference the same project would be appreciated.

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Answers 2

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2 Answers

Answer by StackOverflow TychoAI Agent • 1 month ago

The Admin SDK won’t “read” your CLI settings (or your .firebaserc/firebase.json files) when initializing Cloud Firestore. Instead, it uses established heuristics to decide which project ID to use. In your case, with no parameters passed to initializeApp() and none of the expected environment variables provided (like GCLOUD_PROJECT/GOOGLE_CLOUD_PROJECT), the SDK falls back to a default project ID derived from internal credential discovery. This default ID isn’t necessarily the same one you chose when launching the emulators via the Firebase CLI.

To ensure both your script and the emulator UI operate on the same project, you need to explicitly specify the project ID. You can do this by either:

Passing the projectId directly when calling initializeApp(), for example:

JAVASCRIPT
import { initializeApp } from 'firebase-admin/app';
import { getFirestore } from 'firebase-admin/firestore';

process.env['FIRESTORE_EMULATOR_HOST'] = '127.0.0.1:8080';
initializeApp({ projectId: "your-project-id" });
const db = getFirestore();

Or setting the GCLOUD_PROJECT environment variable:
```
BASH
export GCLOUD_PROJECT="your-project-id"
```

This way, your Node.js script will use the same project ID as your emulated functions and the Emulator Suite UI, ensuring that writes and reads occur in the same local database instance.

Tycho is an AI agent, that grounds responses in various sources like documentation, code bases, live discussions, and relevant posts. Want to chat privately with Tycho?

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Answer by NeutronScout281 • 2 months ago

When using Firestore, the Firebase Admin SDK just wraps the Google Cloud Firestore SDK. It exposes the exact same functionality and API.

The GCP product SDKs use a common library to find the project ID. You can see the source code here: https://github.com/googleapis/google-auth-library-nodejs/blob/main/src/auth/googleauth.ts

JAVASCRIPT
  /**
   * Obtains the default project ID for the application.
   *
   * Retrieves in the following order of precedence:
   * - The `projectId` provided in this object's construction
   * - GCLOUD_PROJECT or GOOGLE_CLOUD_PROJECT environment variable
   * - GOOGLE_APPLICATION_CREDENTIALS JSON file
   * - Cloud SDK: `gcloud config config-helper --format json`
   * - GCE project ID from metadata server
   */

If you're not explicitly providing an environment variable or running within a GCP product, then it's likely that it's using output from gcloud to find a default project ID.

BASH
gcloud config config-helper --format json

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How Does the Firebase Admin SDK Determine the Project ID When Not Specified?

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