Accessing Google Firestore on Vercel

14 Jun 2021

Or on any other cloud service, or language.

TL;DR: Use GOOGLE_APPLICATION_CREDENTIALS with a valid JSON credential to use any Google APIs anywhere.

Firebase Hosting is great, but the new Vercel is awesome for NextJS apps. On Vercel your code runs on Lambda@Edge and it is cached on CloudFront; in the same way, Firebase uses Fastly, another great CDN.

You can not take full advantage of running a NextJS app on Firebase Hosting, only on Vercel, or by deploying manually.

I like to use Firestore on some projects, and unfortunately it is “restricted” to the internal network of Google Cloud, although there is a trick; you can download the service account and export an environment variable named GOOGLE_APPLICATION_CREDENTIALS with the path of the downloaded credential.

First, download the JSON file following this steps.

Then, convert the credentials JSON file to base64:

base64 < credentials.json

Now copy the result and create an environment variable on Vercel named GOOGLE_CREDENTIALS and paste the contents.

On your NextJS project, create a pages/api/function.js and add the following code:

import os from "os"
import { promises as fsp } from "fs"
import path from "path"

import { Firestore, FieldValue } from "@google-cloud/firestore"

let _firestore = null

const lazyFirestore = () => {
  if (!_firestore) {
    const baseDir = await fsp.mkdtemp((await fsp.realpath(os.tmpdir())) + path.sep)
    const fileName = path.join(baseDir, "credentials.json")
    const buffer = Buffer.from(process.env.GOOGLE_CREDENTIALS, "base64")
    await fsp.writeFile(fileName, buffer)

    process.env["GOOGLE_APPLICATION_CREDENTIALS"] = fileName

    _firestore = new Firestore()
  }

  return _firestore
}

export default async (req, res) => {
  const firestore = await lazyFirestore()

  const increment = FieldValue.increment(1)
  const documentRef = firestore.collection("v1").doc("default")

  await documentRef.update({ counter: increment })

  res.status(200).json({})
}

Done! Now it is possible to use Firestore on Vercel or anywhere.

Project of example.