Well that's not Op's question. They're asking "if I use Minio in my stack without modifications (as a file server that my other services interact with via an API), do I have to AGPL all the stuff the touches Minio or not?" (Minio is basically a FOSS S3) [0]. You're asking about linking, which is covered in the FAQ [1]:
"You have a GPLed program that I'd like to link with my code to build a proprietary program. Does the fact that I link with your program mean I have to GPL my program?"
"Not exactly. It means you must release your program under a license compatible with the GPL (more precisely, compatible with one or more GPL versions accepted by all the rest of the code in the combination that you link). The combination itself is then available under those GPL versions."
I'm not sure that interpretation is correct. I don't read the intention that way (but I'd have to reread the licenses on detail to refresh myself before speaking more definitively).
I mean, they have a strong incentive to get you to buy a commercial license. I'm not surprised they're uninterested in giving you free legal advice in service of not paying them.
If you diff them, you'll see the AGPLv3 is essentially the GPLv3 with this extra clause added:
"13. Remote Network Interaction; Use with the GNU General Public License.
Notwithstanding any other provision of this License, if you modify the
Program, your modified version must prominently offer all users
interacting with it remotely through a computer network (if your version
supports such interaction) an opportunity to receive the Corresponding
Source of your version by providing access to the Corresponding Source
from a network server at no charge, through some standard or customary
means of facilitating copying of software. This Corresponding Source
shall include the Corresponding Source for any work covered by version 3
of the GNU General Public License that is incorporated pursuant to the
following paragraph."
Therefore, what I said about linking applies to both.
To be clear, you only have to offer source code if you've modified an AGPLv3 program and you're distributing it publicly or "interacting with it remotely through a computer network (if your version supports such interaction)". Op's scenario neither modifies Minio nor distributes it, so they're under no obligation to offer source.
If connecting over the network doesn't constitute linking in a way that imposes AGPL obligations, then Google's position, or the reason they state for it, (https://opensource.google/documentation/reference/using/agpl...) is simply wrong. No offence, but I'm going to believe their expensive legal team not being able to find a way around this means that your interpretation is not correct.
Ha well, as a lover of spirited conversation I am not at all offended. I'm not telling you you have to use (A)GPL code, I'm just trying to dispel various rumor.
I really, truly believe the GPLs have revolutionized our society. It's hard to imagine the internet and tech looking as good as they do (they could look way, way worse) without copyleft. Somewhere along the way we adopted this simplistic, hypothetical conception of freedom as "fewer restrictions and obligations", but experience gives us numerous counterpoints. Who is more free, the citizen of a country that protects against robbery, fraud, and violence, or the denizen of a lawless land? Oftentimes restricting one freedom (the freedom to kill, the freedom to close source) unlocks untold other freedoms (freedom to speak or worship without violence, freedom to build Google et al on the back of FOSS software). We've weirdly forgotten this, and I'm doing what I can to remind us.
That Google policy is actually heartening to me. It means that if I build some successful infra app and license it under the AGPLv3, there's zero chance I'll see it show up in GCP. That's a mission accomplished as far as I'm concerned.
"You have a GPLed program that I'd like to link with my code to build a proprietary program. Does the fact that I link with your program mean I have to GPL my program?"
"Not exactly. It means you must release your program under a license compatible with the GPL (more precisely, compatible with one or more GPL versions accepted by all the rest of the code in the combination that you link). The combination itself is then available under those GPL versions."
[0]: https://min.io/
[1]: https://www.gnu.org/licenses/gpl-faq.html#LinkingWithGPL