I understand the question mark about what it is that Amazon did wrong here, and for the most part I agree that they've done nothing wrong.
But I am not Amazon's side here. This is my very subjective take on the matter and by no means am I claiming to be correct.
Amazon represents and existential threat to the open source business model. To those who say otherwise: How do you compete with a company with the incredible amount of resources available to Amazon? They could outprice you (running at a loss) and use that as leverage to bring your customers into their ecosystem.
I'm not saying Amazon is actively hostile towards opensource. I recognise that they even submit contributions to the stacks they use (at least the ones I've seen). But there's no argument that I could host a better instance than Amazon. That would be one hell of a grandiose delusion.
I don't know what the answer is here for open source. Maybe a license that allows free use, but prohibits you directly competing (offering a paid solution for support of the product) without a license.
I don't think that's unfair stance to take, it doesn't punish Amazon for being such an incredibly successful and powerful hosting provider (I like AWS, I really hope I'm not sounding hostile towards them) but it creates a symbiotic relationship instead of a directly competitive one.
Maybe I'm being naive and overlooking something, but I don't see what choices Elastic had here.
I don't agree with the arguments that Elastic made a killing last year and therefore they should shut up and be grateful. Be grateful for what, exactly? That a behemoth of a platform is taking business share from them? You can't expect them to be OK with that, surely. I don't agree with their response either, but I think it's time the open source community acknowledges that we're in a different era now and we need a license to reflect that.
1. Don't punish Amazon, they haven't done anything wrong (and you can very easily nuke small businesses that offered support too, nobody is whining about them). Open source should belong to all of us. Making money off of that should really belong the original authors. I don't think that's a wildly ridiculous opinion.
2. Protect your business model, or maybe even come up with a new one that works hand-in-hand with a hosting provider like Amazon, rather than waiting for them to drain your market (which is not their intention but you can't ignore that it's happening).
An example I can think of for 2) is building a version of the product that's more suitable for Amazon, which might help relieve overhead for them setting that product up. Then charge them for supporting that codebase. I'm imagining a twist of the "enterprise-grade" tier with extra features for enterprise-grade users. Have a "cloud-provider" tier on top of that (that supports replication, multi-instance, easy-up-down state or whatever you can think of).
Again: I'm just a dude who thinks there's a growing elephant in the room that can be addressed in a manner that's beneficial to all parties. I don't mean to attack Amazon or Elastic, but I think this incident is a harbinger for what's to come
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EDIT: Maybe the right move is to approach the cloud providers as an OSS provider and ask them to work with you on your business model. Don't wait for Amazon to build your product into an offering, build it with them. Take a cut of the revenue. Maybe?