Can Firebase Hosting Serve Cached Data from Cloud Functions?

This is a good use-case for JAMstack style architecture where you pre-render your pages, and at build-time load the data you need. You can think of pre-rendered static site builders as just another form of caching. In this case, given your expectation of once-per month updates, it doesn't even really make that much sense to be server-rendering your pages at runtime at all.

When your data changes, just rebuild your site. Gastby (in the react world) is setup for this and has many different data sources that plug in to the builder, including a plugin for firestore.

Netlify is a static-site host that has webooks to trigger a rebuild. You can use a firebase cloud function triggered by events to various firestore collections/documents that pings Netlify to run "build" upon inserts/updates/deletes.

Not only is this cheaper, it is less complex than running run-time servers, and provides highest end-user performance as static pages load quickest.

On top of setting the Cache-Control header, you can utilize the benefits of global variables setup in your Cloud Functions instances, see Cloud Functions Tips where they mention "Use global variables to reuse objects in future invocations".

With that idea, I am able to use the npm package treasury (yes I did develop this but that is unrelated to the fact that it happens to work with this use case in Cloud Functions - also I use it in production if it makes you feel better).

Example that will utilize the "Memory" adapter of Treasury to store data as long as the variable treasury exists, which lives and dies with the Cloud Function instance:

const functions = require('firebase-functions');
const tauist = require('tauist');
const Treasury = require('treasury');
const cors = require('cors')({
    origin: true
});

// note that memory adapter uses MS not S for ttl
const treasury = new Treasury({
    ttl: tauist.ms.thirtyMinutes
});

function getAnimalData({name}) {
    // replace this with your actual Promise code doing the "real work" that you want to cache
    return new Promise();
}

exports.animal = functions.https.onRequest((req, res) => {
    if (req.method !== 'GET') {
        return res.status(403).send('Forbidden');
    }

    // Enable CORS using the `cors` express middleware.
    return cors(req, res, () => {
        // Reading ticker symbol from URL query parameter.
        let name = (req.query.name || '').trim();
        console.log('animal name:', name);

        if (!name) {
            return res.status(400).send('Bad Request');
        }

        res.set('Cache-Control', `public, max-age=${tauist.s.thirtyMinutes}, s-maxage=${tauist.s.thirtyMinutes}`);
        treasury.invest(getAnimalData, {name})
            .then((data) => res.status(200).send(data))
            .catch((error) => {
                console.error('error caught:', error);
                res.status(500).send('Internal Server Error');
            });

    });
});

When you use Firebase Hosting on top of Cloud Functions for Firebase, Hosting can act as an edge-cached layer on top of the responses from your HTTPS functions. You can read about that integration in the documentation. In particular, read the section managing cache behavior:

The main tool you'll use to manage cache is the Cache-Control header. By setting it, you can communicate both to the browser and the CDN how long your content should be cached. In your function, you set Cache-Control like so:

res.set('Cache-Control', 'public, max-age=300, s-maxage=600');