75 lines
3.6 KiB
Markdown
75 lines
3.6 KiB
Markdown
---
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layout: post
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title: 'Katja: Riemann Client Written In Erlang'
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description: "Introductory post about the Riemann client I've written."
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date: 2014-05-04 21:55:00 CEST
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category: posts
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tags: [erlang, programming, riemann, katja, english]
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comments: true
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---
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[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.
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Katja supports all the basic things a Riemann client has to support. It can ...
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- ... send events
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- ... send states
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- ... query events
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Additionally multiple events and states can also be send in a single message.
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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.
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## Sending Events
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{% highlight erlang linenos %}
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Event = [{service, "katja demo"}, {metric, 9000.1}],
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ok = katja:send_event(Event),
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Event2 = [{service, <<"katja demo">>}, {metric, 9000.1}, {tags, ["demo"]}],
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ok = katja:send_events([Event, Event2]).
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{% endhighlight %}
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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.
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The entire `katja:event()` type definition can be found on [GitHub](https://github.com/nifoc/katja/blob/v0.1/src/katja.erl#L31..L33).
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## Sending States
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{% highlight erlang linenos %}
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State = [{service, "katja demo"}, {state, "testing"}],
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ok = katja:send_state(State),
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State2 = [{service, "katja demo"}, {state, "testing"}, {tags, ["demo"]}],
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ok = katja:send_states([State, State2]).
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{% endhighlight %}
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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.
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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).
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## Querying Events
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{% highlight erlang linenos %}
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{ok, Events} = katja:query("service = \"katja demo\"").
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{% endhighlight %}
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`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).
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You can find example queries in the [Riemann test suite](https://github.com/aphyr/riemann/blob/master/test/riemann/query_test.clj).
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## Sending Entities
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{% highlight erlang linenos %}
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Event = [{service, "katja demo"}, {metric, 9000.1}],
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State = [{service, "katja demo"}, {state, "testing"}],
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ok = katja:send_entities([{events, [Event]}, {states, [State]}]).
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{% endhighlight %}
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Katja also allows you to send mutiple events and/or states in a single request via `katja:send_entities/1`.
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## Future
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There are two things I'm currently thinking about adding to Katja:
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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.
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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.
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