I kind of see this as a general trend where CoreOS is concerned they reimplement everything in house, even when open source solution might already exist - rkt, etcd, now this.
For Etcd I'm of two minds. I like its simplicity. On the other hand, I have had far more problems with Etcd than I've ever had with e.g. Consul (though I dislike Consuls "and the kitchen sink" approach), up to and including data loss and more than once having to re-initialise clusters. I'm a couple of years of no further problems at least a way from trusting Etcd with my data.
For this? They have to have very compelling stories for why they couldn't e.g. modify Ceph or Gluster to achieve whatever it is that they want. And it's no clear what they want. Gluster for example is built as a stack of pluggable translators that is relatively easy to extend.
Even if they have a credible and compelling story for why we need something else, it will take years of production use by others before I'd trust any data to a new distributed file system.
Gluster and Ceph have those years. I've had a Gluster volume running without maintenance or data loss for more than five years. Even then it took several years before I truly started to trust it.
Gluster had many issues too when it was a young project, but they were fixed many years ago. I don't doubt that Etcd too will become solid enough for me to trust, but looking at part of the docs [1] we still have "gems" such as "Permanent Loss of Quorum Requires New Cluster" (you don't lose your data to that one, but it's painful nevertheless).
And yes, I've run into that one. Not "permanent" as in "we could never recover the machines in question", but "permanent" as in "we're not going to be able to get this sorted fast enough, so let's fail everything over". Everything else we run can handle that scenario easily. We know it means consistency issues, but if you run into that situation we have taken the decision that they are acceptable and will be resolved later if necessary. The last thing I need in a scenario like that is for some critical component to just refuse to run without requiring lots of manual intervention.
All we'd like would be to be able to say "ok, drop all the other members and pretend all is well, and yes we know what we're asking". There are a number of gotcha's like that with Etcd that sounds find until they bite you in the ass.
They'll resolve these things eventually, but storage is the very last place I'd be willing to take risks with it. So until they have years of track record of running flawlessly, with less hassle than Gluster or Ceph, and substantial advantages, I'll see it as the dangerous choice.
[1] https://coreos.com/etcd/docs/latest/runtime-reconf-design.ht...
How many separate data centres do you want me to host in? Two is certainly insufficient, as if the data centre with the majority of Etcd nodes now falls of the network, you're SOL.
Three? Think you can't have two fall of face of the earth the first time? Been there. Redundant connections doesn't always help if there are major external connectivity issues and you don't have multi-million dollar budgets for connectivity alone.
Most small to mid size companies do not have the budget to run a system that is sufficiently redundant to be able to guarantee that they won't sooner or later be in a situation where either 1) the most viable partition is the minority, or 2) the Etcd cluster is centralised enough that too large parts of the cluster can loose access to it. When fighting large scale failures is the last time where you want to have to fight your tools to be able to convince them that you know what you're doing.
For those kind of situations, Etcd's lack of support for more fine-grained control of consistency or for intentionally breaking apart the cluster and letting them continue to operate independently when you know what you're doing basically makes it unsuitable for running multi-data centre clusters for anything important.
Which basically means any tools that assumes a single underlying Etcd cluster is appropriate as storage, for, say, a cluster scheduler (cough) becomes an inappropriate tool for those kind of setups.
And it generally seems that, when they say "composable modular tools", one should read "includes dependencies on the rest of our stack". This isn't intended as harshness. It is just that every time a tool from COS seems interesting enough to look in to, it turns out that I wouldn't be investing in a tool, it would be investing in an ecosystem that duplicates a ton of what I'm already managing.
https://en.wikipedia.org/wiki/Clustered_file_system#Distribu...
I write this not as storage religion (of which there's far too much), but to warn away those who haven't experienced the many kinds of data (and stomach lining) loss that come with being a Lustre admin.
http://sector.sourceforge.net/
I swore I added it to the Wikipedia links. I'll have to do it again, I guess.
(disclaimer: I'm an engineer there...)
I thought Elasticsearch was open-sourced, and the GitHub repo says Apache v2. What am I missing here?