As far as I understand, my Google Cloud Functions are globally accessible. If I want to control access to them, I need to implement authorization as a part of the function itself. Say, I could use Bearer token based approach. This would protect the resources behind this function from unauthorized access.
However, since the function is available globally, it can still be DDoS-ed by a bad guy. If the attack is not as strong as Google's defence, my function/service may still be responsive. This is good. However, I don't want to pay for those function calls made by the party I didn't authorize to access the function. (Since the billing is per number of function invocations). That's why it's important for me to know whether Google Cloud Functions detect DDoS attacks and enable counter-measures before I'm being responsible for charges.
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/
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.
from reading the docs at https://cloud.google.com/functions/quotas and https://cloud.google.com/functions/pricing it doesn't seem that there's any abuse protection for HTTP functions. you should distinguish between a DDoS attack that will make Google's servers unresponsive and an abuse that some attacker knows the URL of your HTTP function and invokes it millions of times, which in the latter case is only about how much you pay.
DDoS attacks can be mitigated by the Google Cloud Armour which is in the beta stage at the moment
See also related Google insider's short example with GC Security Rules and the corresponding reference docs
