Let's break down your scenario and address each of your questions clearly:

First, a quick recap to make sure I'm aligned: you've got long-term caching set up perfectly for your hashed static assets (CSS, JS, images) with Cache-Control: "public,max-age=31536000"—that's solid since the content hashes change on every deployment, so stale cache isn't an issue there. The tricky part is your index.html, which needs to avoid serving stale versions that point to outdated hashed assets, while still leveraging CDN caching.

1. Is adding s-maxage=86400 to index.html's Cache-Control safe in this scenario? #

Short answer: No, not unless you have a guaranteed way to clear the CDN cache immediately after deploying to Cloud Run.

Here's why:

• The s-maxage=86400 tells Firebase's CDN to cache the index.html for 24 hours.
• Since you're deploying updates to Cloud Run (not Firebase Hosting static files), Firebase has no way to automatically detect that the index.html content has changed.
• For the full 24 hours, the CDN will keep serving the old index.html to users, which references the now-outdated hashed static assets. This will lead to broken pages (404s for missing assets) for any user who hits the cached CDN version before the 24 hours are up.

The must-revalidate directive only helps if the CDN checks back with your Cloud Run server to see if the content is fresh—but Firebase Hosting's CDN doesn't automatically do this for proxied requests unless the cache has expired. So during that 24-hour window, stale content stays served.

2. Is there a way to manually clear the CDN cache if Cloud Run deployments don't trigger it automatically? #

Absolutely! Firebase Hosting has a dedicated command to clear the entire CDN cache, no deployment required:

firebase hosting:clear

This command will purge all cached content from Firebase's CDN for your hosting site, regardless of whether you've deployed new static files or not. It's exactly what you need to run right after deploying a new version to Cloud Run—this ensures the CDN starts pulling the fresh index.html from your updated Cloud Run service immediately.

3. Will running firebase deploy --only hosting clear the cache even if the /public folder is empty? #

Yes, it will. Even if your /public folder has no changes (or is empty), executing firebase deploy --only hosting will trigger a deployment, and Firebase Hosting automatically clears the CDN cache as part of the deployment process.

That said, using firebase hosting:clear is more efficient here—it skips the deployment step entirely and just purges the cache, which is exactly what you need when you're only updating Cloud Run and not touching Firebase Hosting's static assets.

Bonus Recommendation #

If you want to balance CDN caching benefits with minimal stale content risk, consider adjusting your index.html's Cache-Control to:

Cache-Control: "public, max-age=60, s-maxage=86400, must-revalidate"

• max-age=60 tells client browsers to revalidate the index.html with the CDN every 60 seconds, so even if the CDN has a stale copy, users will get the fresh version within a minute.
• s-maxage=86400 still lets the CDN cache the content for a day to reduce origin load.
• Pair this with running firebase hosting:clear after every Cloud Run deployment, and you'll get the best of both worlds: CDN caching efficiency and near-instant content freshness for users.

内容的提问来源于stack exchange，提问作者cbdeveloper