Add Katja v0.1 post

_posts/2014-05-04-katja-riemann-client-written-in-erlang.md

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+---
+layout: post
+title: 'Katja: Riemann Client Written In Erlang'
+description: "Introductory post about the Riemann client I've written."
+date: 2014-05-04 21:55:00 CEST
+category: posts
+tags: [erlang, programming, riemann, katja, english]
+image:
+  feature: header/abstract-11.jpg
+  credit: dargadgetz
+  creditlink: http://www.dargadgetz.com/ios-7-abstract-wallpaper-pack-for-iphone-5-and-ipod-touch-retina/
+comments: true
+share: true
+---
+
+[Riemann](http://riemann.io) is a network monitoring system written in Clojure, it offers a rather simple [protobuf](https://de.wikipedia.org/wiki/Protocol_Buffers)-based API. I have just tagged [Katja](https://github.com/nifoc/katja) [version 0.1](https://github.com/nifoc/katja/tree/v0.1), my Riemann client written in Erlang.
+
+Katja supports all the basic things a Riemann client has to support. It can ...
+
+- ... send events
+- ... send states
+- ... query events
+
+Additionally multiple events and states can also be send in a single message.
+
+Katja only supports Erlang/OTP R16B01+. This is mostly because in releases before R16 `query` was an unused keyword, meaning that you could not easily use it as a function name or record field.
+
+## Sending Events
+
+{% highlight erlang linenos %}
+Event = [{service, "katja demo"}, {metric, 9000.1}],
+ok = katja:send_event(Event),
+Event2 = [{service, <<"katja demo">>}, {metric, 9000.1}, {tags, ["demo"]}],
+ok = katja:send_events([Event, Event2]).
+{% endhighlight %}
+
+Katja allows you to send either a single event or multiple ones. Events are simple property lists with the following (possible) keys: time, state, service, host, description, tags, ttl, attributes, metric.
+
+The entire `katja:event()` type definition can be found on [GitHub](https://github.com/nifoc/katja/blob/v0.1/src/katja.erl#L31..L33).
+
+## Sending States
+
+{% highlight erlang linenos %}
+State = [{service, "katja demo"}, {state, "testing"}],
+ok = katja:send_state(State),
+State2 = [{service, "katja demo"}, {state, "testing"}, {tags, ["demo"]}],
+ok = katja:send_states([State, State2]).
+{% endhighlight %}
+
+States and events are very similar, so much so that the (possible) keys of a state property list are almost identical to the keys of an event property list: time, state, service, host, description, tags, ttl, once.
+
+Once again, the entire `katja:state()` type definition can be found on [GitHub](https://github.com/nifoc/katja/blob/v0.1/src/katja.erl#L34..L36).
+
+## Querying Events
+
+{% highlight erlang linenos %}
+{ok, Events} = katja:query("service = \"katja demo\"").
+{% endhighlight %}
+
+`katja:query/1` will return a list of events. Events are a property list of type `katja:event()`, so what you send to Riemann is also what you get back when querying. There is one important thing to keep in mind: All `undefined` or `[]` values will be removed from the returned property list(s).
+
+You can find example queries in the [Riemann test suite](https://github.com/aphyr/riemann/blob/master/test/riemann/query_test.clj).
+
+## Sending Entities
+
+{% highlight erlang linenos %}
+Event = [{service, "katja demo"}, {metric, 9000.1}],
+State = [{service, "katja demo"}, {state, "testing"}],
+ok = katja:send_entities([{events, [Event]}, {states, [State]}]).
+{% endhighlight %}
+
+Katja also allows you to send mutiple events and/or states in a single request via `katja:send_entities/1`.
+
+## Future
+
+There are two things I'm currently thinking about adding to Katja:
+
+1. Adding (generic) support process pools: This should be done in a way that does not assume anything about the pool that's being used. Katja will not depend on a specific process pool implementation.
+
+2. Querying based on a property list: This means that you could pass a property list of type `katja:event()` to a query method and get back events based on that. In general, all it should take to do this is transforming the property list in a query string that Riemann understands.