Are Google Cloud Functions protected from DDoS attacks?

I have sent an email to google-cloud support, regarding cloud functions and whether they were protected against DDoS attacks. I have received this answer from the engineering team (as of 4th of April 2018):

Cloud Functions sits behind the Google Front End which mitigates and absorbs many Layer 4 and below attacks, such as SYN floods, IP fragment floods, port exhaustion, etc.

I have been asking myself the same question recently and stumbled upon this information. To shortly answer your question: Google does still not auto-protect your GCF from massive DDOS-attacks, hence: unless the Google infrastructure crashes from the attack attempts, you will have to pay for all traffic and computing time caused by the attack.

There is certain mechanisms, that you should take a closer look at as I am not sure, whether each of them also applies to GCF:

• https://cloud.google.com/files/GCPDDoSprotection-04122016.pdf
• https://projectshield.withgoogle.com/public/

UPDATE JULY 2020: There seems to be a dedicated Google service addressing this issue, which is called Google Cloud Armor (Link to Google) as pointed out by morozko.

I think the question about DDOS protection has been sufficiently answered. Unfortunately the reality is that, DDOS protection or no, it's easy to rack up a lot of charges. I racked up about $30 in charges in 20 minutes and DDOS protection was nowhere in sight. We're still left with "I don't want to pay for those function calls made by the party I didn't authorize to access the function."

So let's talk about realistic mitigation strategies. Google doesn't give you a way to put a hard limit on your spending, but there are various things you can do.

Limit the maximum instances a function can have

When editing your function, you can specify the maximum number of simultaneous instances that it can spawn. Set it to something your users are unlikely to hit, but that won't immediately break the bank if an attacker does. Then...

Set a budget alert

You can create budgets and set alerts in the Billing section of the cloud console. But these alerts come hours late and you might be sleeping or something so don't depend on this too much.

Obfuscate your function names

This is only relevant if your functions are only privately accessed. You can give your functions obfuscated names (maybe hashed) that attackers are unlikely to be able to guess. If your functions are not privately accessed maybe you can...

Set up a Compute Engine instance to act as a relay between users and your cloud functions

Compute instances are fixed-price. Attackers can slow them down but can't make them break your wallet. You can set up rate limiting on the compute instance. Users won't know your obfuscated cloud function names, only the relay will, so no one can attack your cloud functions directly unless they can guess your function names.

Have your cloud functions shut off billing if they get called too much

Every time your function gets called, you can have it increment a counter in Firebase or in a Cloud Storage object. If this counter gets too high, your functions can automatically disable billing to your project.

Google provides an example for how a cloud function can disable billing to a project: https://cloud.google.com/billing/docs/how-to/notify#cap_disable_billing_to_stop_usage

In the example, it disables billing in response to a pub/sub from billing. However the price in these pub/subs is hours behind, so this seems like a poor strategy. Having a counter somewhere would be more effective.

This is from my own, real-life, experience: THEY DON'T. You have to employ your own combo of rules, origin-detection, etc to protect against this. I've recently been a victim of DDoS and had to take the services down for a while to implement my own security wall.