Call functions via HTTP requests | Trigger a function with an HTTP request | Limitations

I really have hard time to build my app because of cloud function documentation (usage and limitations). I don't understand

I have a question,
In my app, I don't want to allow direct client-side read requests to firestore database. (client-side -> firestore database with security rules)

match /users/{document=**} {
  allow read: if false;
  allow write: if false;
}

But, I have to allow requests from client-side user through invocating a http async request or on call request. (end-user -> cloud-functions -> firestore database)

question is, Does cloud function manage scalability and load balancing techniques facing lot of traffics(100k user read requests) at a same time via http async request or app onCall request?

Example, what if 100k user request to getusers in same time?

const functions = require('firebase-functions');
const admin = require('firebase-admin');
admin.initializeApp();

exports.getUsers = functions.https.onRequest(async (req, res) => {
  try {
    const usersCollection = admin.firestore().collection('users');

    // Query for online male users with limit 5
    const querySnapshot = await usersCollection
      .where('isOnline', '==', 'online')
      .where('gender', '==', 'male')
      .orderBy('last-active', 'desc')
      .limit(5)
      .get();

    const userList = [];
    querySnapshot.forEach((doc) => {
      const user = doc.data();
      userList.push(user);
    });

    res.status(200).json(userList);
  } catch (error) {
    console.error('Error retrieving users:', error);
    res.status(500).send('Error occurred');
  }
});

> Does cloud function manage scalability and load balancing techniques facing lot of traffics(100k user read requests) at a same time via http async request or app onCall request?

Yes, it will scale up as needed to handle the requests as needed.

You should review the documentation to understand its behavior:

> Cloud Functions implements the serverless paradigm, in which you run your code without worrying about the underlying infrastructure, such as servers or virtual machines. Once deployed, your functions are automatically managed and scaled.
>
> Cloud Functions handles incoming requests by assigning them to instances of your function. Depending on the volume of requests, as well as the number of existing function instances, Cloud Functions may assign a request to an existing instance or create a new one.
>
> In cases where inbound request volume exceeds the number of existing instances, Cloud Functions may start multiple new instances to handle requests. This automatic scaling behavior allows Cloud Functions to handle many requests in parallel, each using a different instance of your function.

You do not get an absolute performance guarantee, but you do get this scaling behavior at no extra cost.