samza-config

Samza jobs. In idiomatic Clojure

Rationale

Samza takes care of a lot of quite difficult problems and while it would be fun to solve them in Clojure (in-fact some people are doing that and more), it's hard to justify the time it would take when you've got business features to deliver. We want to allow app developers to focus on the business logic of their app.

Ideally, you could write a plain old clojure function, and somehow arrange for Samza to invoke it on each new message it is interested in. The intention of this project is to provide the "somehow arrange for" part.

Implementation

We do this by implementing a few key features

• A suite of functions that take a function as input, and use reify to build an implementation of the corresponding samza interface

• A defjob macro that registers the job and allows for it's configuration to be generated

• A config rewriter that pulls a job-id from the environment and generates the samza config on the fly

Usage

I'm still playing around with the syntax of defjob but it should look something like this. Here's the standard LinkedIn scale word-counter.

Update:

The syntax is stabilizing a bit. The job below defines a working samza job that assumes email-task implements the StreamTask interface and submits an email if one hasn't already been sent. This also decodes messages using confluent's schema registry. Read more about that here

http://docs.confluent.io/1.0.1/schema-registry/docs/index.html

(ns example.word-counter
  (:require
   [samza-config.core :refer [local-storage job-coordinator task-factory]]
   [org.apache.samza.serializers StringSerdeFactory]))

(defn word-counter [config context]
  (let [store (local-storage context "word-counts")]
    (reify
      StreamTask
      (process [this envelope collector coordinator]
        (let [word (.getMessage envelope)]
          (swap! store update-in [word] (fnil inc 0)))))))

(defjob word-counter
  {:job {:factory thread-job-factory
         :coordinator (job-coordinator "word-counter" (env :coordinator-replication-factor))
         :task {:factory (task-factory 'word-counter)}}

   :systems {:word-counter
             {:samza {:factory kafka-system-factory}
              :streams (input-streams
                        (input-topic "words" :string :string))
              :consumer (env :zk-addr)
              :producer (env :kafka-addr)}}

   :serializers {:registry
                 {"string" {:class StringSerdeFactory}}}

   :stores (stores
            (kv-store "word-counts" :edn :edn))

   :task {:class "samza-config.task.Task"
          :inputs (task-inputs "words")}})

Samza jobs are typically deliverable as tarballs so we include a helper that knows how to build one.

$ lein run -m samza-job.build tarball

Assuming the job above, this will package the job and write it to target/word-counter.tar.gz

License

Copyright © 2015 Andy Chambers

Distributed under the Eclipse Public License either version 1.0 or (at your option) any later version.