Just to add a bit more nuance, I think we tend to focus a lot on community contributions, but IMO the biggest benefit of FOSS is not that; it's adoption.
Even if Elastic writes 100% of the code, by making it open source, they are promoting the widespread adoption of their software. A project with a non-free license or a custom license is a non-starter at many (most?) companies, or at a minimum requires talking to legal which is a PITA.
So, even with no community contributions, Elastic would never have been able to get to where they're at now - making $500MM in revenue a year and at a $15B evaluation - if it weren't open source.
Now just to be clear, Elastic is totally allowed to close things up now that they've reaped the benefits. The beautiful irony is that, when you close source after you've reaped the benefits, by definition you've also hit the point where it's now obviously beneficial for a company like Amazon to make their own fork and keep their AWS Elasticsearch cash cow going.
So, ultimately the community is totally fine. Indeed Elastic has been going down this road for a few years now, so it's actually a good thing for us that this happened. Better to have an amicable divorce early rather than a messy one later. But I can't help but point out that Elastic has broken its promises and misled the community - to their detriment more than to ours.
This isn't an accident, it's in fact the whole point of open source that people can make open source forks when the original authors decide to no longer do open source.
I don't think there's much 'amicable' about it though in this case at the moment.
I don't think that's true, at least for software such as Elastic, Mongo and RedisLabs.
There are a lot of big companies that benefit from those, and might want to invest it, despite not being their direct revenue driver.
See for example the Cassandra database released by Facebook. Or how Amazon is going to invest in their Elastic fork now. Or how Linux is funded by dozens of companies (IBM, RedHat, Oracle...)
Or pretty much any programming language: I haven't seen a programming language that's not truly Open Source (as in the compiler/interpreter + API) for decades.
The kind of software where it's not going to work is where it's solving a business need for companies that are not software companies: but Open Source isn't common in those fields anyway.
https://news.ycombinator.com/item?id=25867682
Do they want to have their cake and eat it too?
Elastic (and Mongo and RadisLabs) are trying to do something new.
Linux, without doubt, "reaped the benefits of open source, including free work from the community," to the point where although the original release was 100% Linus's own code and arguably "Linus's software", these days to a first approximation _none_ of the code is "his". The percentage of the ~27million LOC that is "linux" these days that were personally written by Linus is effectively zero.
Elastic is a company paying 500-1000 employees who I suspect (but haven't checked) contributed the majority of the code rather than it being "free work from the community". (And their ability to relicense the code suggests that any community contributed code was contributed under their CLA which meant the contributors explicitly granted Elastic future rights to relicense those contributions, so it's not like the "community" can pretend they didn't know this was possible.)
I don't know that Elastic's business model will work. I don't think there's any guarantee that it will. Part of me kinda hopes it does, because I suspect that the business success of "company backed venture capital funded free-as-in-beer software" might result in more and better software being available to use - perhaps software on such a large scale that "scratch your own itch" motivations have insurmountable ramp up difficulties. I personally think the jump[ from AntiRez's "scratch your own itch" redis, to RedisLab's "Widely Fortune500 adopted and enterprise ready Redis" is not a thing AntiRez wanted to stick around and do. And the world _might_ be a better place for the existence of the non-OSI approved software under license like RedisLabs "source available" one.
It'll be interesting t watch this play out over the next decade or so...