What's it all about
Whatever services you are running, there always a need for monitoring. You want to know that you service is down before you customers or bosses fire you :) There are a lot of open source software and hosted services for that, but services are usually featureless or costly (or both) and open source solutions are often featureless and outdated as well. But some of them are different.
Shinken's core was divided into several separated services: arbiter, scheduler, broker, poller, etc. connected over network. It gives both better scalability and better availability. You can host different services on different hosts, double them when needed, and not worry about monitoring while you restart web UI or something for update. Also several things (like web UI, for example, or data retention backend) are, in fact, modules which could be chosen out of several options.
Default web UI is nice, it looks like contemporary web UI should look like, it doesn't use cgi or something that outdated (for technology's sake, cgi, c'mon? it's 2014 already!).
If you were using Nagios before, migration should not be very hard. Quickstart documentation says you can use you Nagios configuration as is, but I would not recommend you to. I'd suggest trying to re-use big amounts of data like hosts descriptions while trying to incorporate other pieces into Shinken's own configuration structure. It would take some time, but it makes sense. Almost all third-party tools (plugins and stuff) will work as well.
Configuration can be loaded from various sources, you can monitor all your AWS instances automatically, or keep configuration in database with some configuration tools, or whatever.
It all may help someone build commercial monitoring service using Shinken. I'd love to see a lot of them around, cheap, feature-rich, and helping to develop great open source tool.
It's under active development so we can expect it to become nicer with every new release.
Well, it's not all good. There some minor disadvantages as well. For example, it heavily relies upon Nagios plugins (they are shell commands, in fact, but it does not matter) and several other tools built for Nagios. It ok, they good, but I'd prefer if they maintain their own fork (with repository similar to modules).
Also several things I found annoying in Nagios are still here. Why, for example, no one wrote notification module using Python library and templates instead of shell pipes and /usr/bin/mail? Apart from other reasons, it might help sending emails with CC/BCC for several receivers and with proper headers to organize emails in threads.
Documentation is far from being up-to-date and full. Especially quick start documentation. I've spent half an hour trying to get web UI working. Several new things (not available in Nagios) may require you to change you configuration structure a bit in order to get all the advantages. Notification filters rely on contact groups, default network service monitoring packs (like http or ssh) rely on templates instead of hostgroups, so you'd need to change all your hosts configurations unless you want to stick with you own custom service configurations, and so on. It's understandable that there are differences, and Shinken's way is usually better one, but when I read quickstart documentation' I'd prefer to see what those differences are.
Shinken's cool. If you are still using Nagios, consider at least trying it (it won't hurt to have both for a while, but you'll quickly realize that you don't need Nagios anymore). If you don't use any monitoring yet, but want to try something, try Shinken. If you arethinking about IT start-up, think about starting monitoring service, there are not much of cheap and feature-rich services out there. If you are Shinken user already, think about sharing some of your experience, tips and tricks with community. Maybe your module or pack is what everyone need? And I will continue to use it whereever I'd used Nagios before. There is nothing about monitoring that Shinken is not able of.
And I'm very eager to see any hosted service using Shinken, that was the one thing Nagios was not capable of at all.