by-builder example

[Fabien Wernli]

Hi,

I'm trying to understand how to use by-builder.

Could anyone share an example please ?

Thanks

[Fabien Wernli]

Adding a little context : I want to build a stateful load-balancer to send to multiple riemann servers.

Here's what I came up with:

(defn forward-balanced-stateful
  "Forwards events to a pool of riemann tcp clients.
   The client is chosen using the event's fields, hence the stateful suffix."
  [clients fields]
  (let [get-relay-idx (fn [event] (mod (hash (select-keys event fields)) (count clients)))]
    (by-builder [idx get-relay-idx] (batch 100 10 (forward (get clients idx))))))

And here's how I'm using it in a stream:

(let [forward_balanced_safe-tcp_clients [(tcp-client :host "remote-riemann-1" :port 5555)(tcp-client :host "remote-riemann-2" :port 5555)]

  (streams (forward-balanced-stateful forward_balanced_safe-tcp_clients [:host :service])))))))

Does that seem correct to you?

[ap...@aphyr.com]

There's an example in the docstring here: https://github.com/riemann/riemann/blob/0.3.10/src/riemann/streams.clj#L1593

Basically by-builder takes a binding form of [symbol by-field] and makes that symbol available in the remaining forms which construct the fork. I agree the docstring is not particularly clear! Took me reading the source to get what was going on.

--Kyle

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