No work at all; basic coreos is just docker managed by systemd. Can you make your application docker-izable? Were you planning on using process management? If you answered yes to both of these questions... :)

Further, coreos tries to make you write applications in a 12-factor-y way, so when the time does come for you to use a million machines, you won't need to make huge adjustments to your deployments (just plug the container and init script into fleet and let it roll).

The main benefit is it's an easy to update, minimal OS. And docker's already set up for you and updated regularly.

Our cloud-config implementation is designed so that you can use the same config to set up a new machine to match an existing one, and have it automatically join the cluster. Start with 3 machines and scale up as you need.

Learning systemd is one bump you'll have to get over, but all of the major distros will be using it, so they're is no better time to try it out.

It is not a lot of work to get started, here is a short and simple tutorial that goes from nothing to a full running app with a database on CoreOS: http://www.centurylinklabs.com/building-your-first-app-on-co...

I'm interested in it because I plan to use docker to ease application management, and with CoreOS I barely have to maintain the operating system because it's so lightweight. So it greatly simplifies things :)

If you think docker is a good fit for your application, this is kind of the next step.

The only significant benefit over traditional operating systems/network services is it's designed to work on flaky hardware and networks. The only use cases i've found for decentralized distributed networks of application services (other than obscure stuff like parallel processing of large datasets) is when you have no guarantees of availability. As far as "scaling", you don't need coreOS to build a scalable network (and i've seen no performance benchmarks of coreOS running on thousands of machines at a time, so I have no idea how well it scales)

"Recoverable system upgrades" - https://coreos.com/blog/recoverable-system-upgrades/

Run from root partition A and only update on partition B, essentially via chroot. Downtime required for updates is the cost of a reboot. If, however, upon an error during boot, reboot into other partition which will be your last known good config.

Seems simple and straight-forward but is difficult for unmodified Debian-based distributions, so they've addressed this as a key feature of CoreOS.

While similar, Serf and Etcd solve a different problem. Etcd is strong consistent (all nodes will see the same data, however a partition may cause the system to not accept writes) while Serf is eventually consistent (all nodes are not guaranteed to see the same data, however the system will always accept writes)

So somethings like a distributed lock is impossible to implement with Serf.

Config data accessible via HTTP instead of files.

Although its not limited to config data necessarily.

I suggest reading http://sysadvent.blogspot.com/2013/12/day-20-distributed-con...

I listed what I like. "Excites" is your word.

I guess what I meant by "from scratch" is that they aren't burdened by legacy code, and aren't limited to using the Paxos algorithm.

If you look at Deis, for example, it basically outsources a lot of node management to Chef Server, which in my view creates a great deal of technical debt on day one.

Probably the fact that you get a single binary (unlike interpreted languages), and that it isn't a mix of Go and C meaning I worries about c libraries.

The functionality to handle this is mentioned in the blog post: "standby" peer mode.

"Our upcoming release, etcd 0.4, adds a new feature, standby mode. It is an important first step in allowing etcd clusters to grow beyond just the peers that participate in consensus."

I don't know that that's necessarily a good idea.

As you (perhaps automatically) expand and collapse the cluster, you'll need to make sure to communicate to all nodes what the new cluster size is. If some nodes don't know the correct quorum count, split-brain!

Also, coordination services are typically critical, so its important to isolate from to the bugs in the adhoc code you're writing for your web tier, a crazy query in your database, etc.

It's much easier and safer in practice to just have 3 or 5 nodes running the coordination in isolation.

Edit: more reasons -- It's easier to deploy a coordination service to 5 nodes than 500. It's easier to debug 5 nodes than 500.