Yes and no. Yes, if we're just specifically talking about the ability to support a free trial that will never bill you (i.e. what the OP was talking about); but no, if we're talking about the more-general ability to set spending limits and never be billed for overage (what this subthread drifted into discussing.)

Oracle Cloud has a 30-day free trial; and that free trial seems to have had some dedicated effort put into a whole divergent billing-infra path for it.

Under Oracle Cloud's free trial, you get a certain amount of spend ($300 in credits); and then, when your trial either expires (30 days) or you run that credit pool down to zero, your account is shut off.

Oracle do eat any marginal costs from your spend taking your credits "below zero" before they shut the account off, because your account was never billing to you anyway; it was billing to Oracle's marketing department as a lead-gen expense.

In other words, unlike Oracle Cloud's steady-state IaaS offering, their free-trial IaaS offering is actually a prepaid (but usage-billed) paradigm — with Oracle being the ones doing the pre-payment.

This works much like an oldschool prepaid phone plan, where you pay in every month to be given a certain number of [expiring/non-"rollover"] minutes/texts/MB of data; and then you get an itemized invoice at the end of the month for how close you came to "using up" each resource that month. And you very well can use up a resource's monthly paid allocation before the end of the month — e.g. "running out of texts" and being unable to send more, rather than those converting into something billed to you. (In a prepaid context, that "converting into being billed" is called "flex" or "pay-as-you-go" [PAYG] billing, and is usually some extra option you would have to enable, if offered at all.)

At scale, prepaid usage-billed systems are also asynchronous; to continue the telecom analogy, most phone-service providers won't re-aggregate your prepaid calling minutes to notice you've run out, until you hang up your current call. Only rarely do they have infra where the billing system can ping the telecom switches' control planes to say "hey, this guy just went over, hang up the call" — and when they do, they only do such checks on a 5-minute/30-minute interval, probably as a scheduled batch query.

But, yes, prepaid systems almost always do just eat any overage generated by this detection gap. This is usually safe, because prepaid systems are almost never elastic to the point that you could accrue nontrivial expenses during that short accounting gap.

When a system is that elastic, a systems architect responds by saying "this should be a postpaid system."

Which means that Oracle Cloud's free trial — insofar as it allows you to make use of truly-elastic resources with per-credit upstream basis costs, like FaaS compute — is probably vulnerable/exploitable. Oracle may sometimes be eating some hefty bills, where people on a free trial have wired their FaaS into a proxy fronting some already-highly-popular service.

This is mostly fine, if you have Oracle's treasury, because you'll still be doing KYC in advance of giving out these trials, so you'll only be letting any given individual do one trial.

But this does put Oracle in the territory of "having to think about people who buy burner identities on the black market [usually for ~$1] to sign up for services using them" + "having to think about people who sign up for their free trial and then sell that free-trial account's credentials on the black market [again, usually for ~$1]."

I haven't checked myself, but I would guess that like any other provider who sees this type of attack (e.g. Hetzner), Oracle Cloud likely has hardened registration flows that reject identities + cards from certain parts of the world; traffic fingerprinting heuristics that immediately shut down free trials if they start up a DDoS attack or the like; etc.

Which is something the other clouds get to skip thinking about entirely, by not having a true "free trial" with a prepaid model, and instead just offering e.g. a one-time $300 sign-up-bonus account credit.

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But remember, we're only talking about the "free trial" here — something you only get access to for the first 30 days.

Oracle's free tier — the thing you have after the first 30 days — is no different than the one every other IaaS offers. It needs a billing account populated by your credit card; there's infrastructure to allow you to automate control-plane actions in response to billing thresholds being hit, but no offering that will wire anything up for you; etc.

In Oracle Cloud's free tier, you can set budget limits that will prevent new costed resources from being leased while your account is over that limit in a given month (which is certainly nice) — but those budget limits don't affect ongoing usage-based-billing of a resource. Your FaaS endpoints will continue to accrue vCPU-seconds of billed usage, until you — or some automation you wrote — shuts them off.