Netlify Functions and Firebase SDK Gotchas

January 15, 2020

In working with the Firebase SDK and Netlify Functions, I ran into a Firebase error and configuration issues in which I'd like to share a solution for.

Recently I was working on a project utilizing Gatsby, Netlify Functions and Firebase (although, more specifically, Firestore). First there is some initial configuration to do when using Netlify Lambda and the Firebase SDK, as per their documentation. Install the required dev package via npm install --save-dev webpack-node-externals. Then, create a directory in the root of your project called config with the file webpack.functions.js.

const nodeExternals = require('webpack-node-externals');

module.exports = {
  externals: [nodeExternals()],

Let's also modify our package.json script to run our lambda functions:

  // ...
  "scripts": {
    "start:lambda": "netlify-lambda serve --config ./config/webpack.functions.js src/lambda",

After setting this up you can get going with your serverless functions. At first glance, my functions connecting to my Firestore data source worked.

Ship it, right?

Not quite. It worked until you hit the an endpoint more than a single time. Making a few more requests made me realize I encountered this error:

Firebase App named '[DEFAULT]' already exists.

After doing some digging, I learned Firebase was trying to be initialized in each cloud function.

const admin = require("firebase-admin");
const serviceAccount =: require("./firebase.json");
  credential: admin.credential.cert(serviceAccount)

// go on to use, query, etc. 
// admin
//   .firestore()
//   .collection(`users`)
//  .get();

But there is a way to solve this. We can initialize Firebase a single time in a helper module, that all of our cloud functions have access to. Then use that instance in any number of cloud functions later on.

// config/firebase.js
const admin = require("firebase-admin");
const serviceAccount = require("./firebase.json");
const app = !admin.apps.length
  ? admin.initializeApp({
      credential: admin.credential.cert(serviceAccount)

export default app

// and consume later on, for example
// src/lambda/update-customer.js
import firebase from "../config/firebase";

Ahhh... perfetto! Crisis averted. What's going on here? We use the apps property and check the length of the array. If we have an app initialized already, just return the instance, otherwise we'll go through the initialization. However, not all is well just yet. Currently, when running locally or in the cloud when deployed to Netlify, we are running against our production Firebase database all the time. Let's fix that. To improve our setup (to hit dev when running locally) it requires some enhancements to our module as well as configuration in Netlify's dashboard.

Navigate to your site's Environment settings under the "Build & deploy" tab (or head to Add an environment variable, I called mine, CLOUD_ENV and gave it the value of production.

Netlify's environment variable settings configuration

Then over in my package.json, I edited my lambda start script to include this variable on the command line. To do this, we'll have to first install Kent's cross-env package. Fire away with npm install --save cross-env. Next, modify your script with the environment variable and value:

  // ...
  "scripts": {
    "start:lambda": "cross-env CLOUD_ENV=development URL=http://localhost:9000 netlify-lambda serve --config ./config/webpack.functions.js src/lambda",

Sweet, we're all set. Now when you test your cloud functions locally, you'll query and manipulate your Firestore documents against some development database you have set up. Push your changes to master (from a pull request, of course), Netlify will deploy to prod for you and automatically point to the right data source.

Hope this helps!

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