Even though we use Grafana only internally and there would be no problem with AGPLv3 in theory I see big meetings with legal coming up which might result in us not being able to use it anymore. I could image that its the same with other corporations. In the end that might hurt the popularity of Grafana quite a lot.
I think that's misunderstanding of AGPL. For internal use, AGPL does not require to share the proprietary part. If a company develop an proprietary UI and use Loki as backend, this is not serving Loki directly to customer, so that does not require company to release their code. It is similar to GPL. Dynamic linking to a GPL software does not require the developer releasing their code. Only provider serving Loki insta…
The key clause is "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."
Would putting AGPL software behind a reverse proxy change the fact that you're a user interacting with it remotely? What about a reverse proxy that changes/adds some headers? What about a really smart reverse proxy that reformats some of the output or repackages it or mixes it with things from other data sources? Is that materially different from the API that powers the "proprietary UI" you're describing?
And say you're pretty confident that you're on the right side of things. Can you point to any case law where courts have established precedent about what "interacting with it remotely" means in this context? No? Then to be on the safe side, you'll probably need to maintain a source code repository for your Corresponding Source, remember to update it every time you update a minor version of the service internally, and maintain an info screen in your product with "prominent" links to that source code repository, which likely means it needs sign off from a product team if not a legal team as well. All things that add expense and barriers to entry.
I think the AGPL is great for services like Grafana's UI itself, where there's likely to be a "human gap" between the software and anyone outside your organization. But things like Loki that are designed to power other proprietary systems that may well be touched by end users through a computer network, where Loki's output may have influence or side effects on the output the user sees? I don't think it's nearly as clear what liability that entails.
(Obligatory: Not a lawyer, the above is not legal advice.)