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Welcome to Finaglezk!

Setup

Scala-bootstrapper has created a fully-functional Scala service for you. You can verify that things are set up correctly by doing:

$ sbt update test

Tutorial

Run your service!

There are two ways to start your service. You can build a runnable jar and tell java to run it directly:

$ sbt package-dist
$ java -Dstage=development -jar ./dist/finaglezk/finaglezk-1.0.0-SNAPSHOT.jar

or you can ask sbt to run your service:

$ sbt 'run -f config/development.scala'

Verify that the service is running

The java/sbt command-lines will "hang" because the server is running in the foreground. (In production, we use libslack-daemon to wrap java processes into unix daemons.) Go to another terminal and check for a logfile. If your server is named "finaglezk", there should be a finaglezk.log with contents like this:

INF [20110615-14:05:41.656] stats: Starting JsonStatsLogger
INF [20110615-14:05:41.674] admin: Starting TimeSeriesCollector
DEB [20110615-14:05:41.792] nio: Using the autodetected NIO constraint level: 0

That's your indication that the server is running. :)

View the Thrift IDL for your service

The IDL for your service is in src/main/thrift/finaglezk.thrift. The Thrift compiler uses the IDL to generate bindings for various languages, making it easy for scripts in those languages to talk to your service. More information about Thrift and how to write an IDL for your service can be found here.

Call your service from ruby

Your service implements simple get() and put() methods. Once you have your server running, as above, bring up a different shell and:

$ cd finaglezk
$ bundle install
$ ./dist/finaglezk/scripts/console
>> $client
>> $client.put("key1", "valueForKey")
>> $client.get("key1")

Look at the stats for your service

By default, your project is configured to use Ostrich, a library for service configuration, administration, and stats reporting. Your config file in config/development.scala defines which port ostrich uses for admin requests. You can view the stats via that port:

$ curl localhost:9900/stats.txt
counters:
  Finaglezk/connects: 1
  Finaglezk/requests: 2
  Finaglezk/success: 2
...

Ostrich also stores historial stats data and can build graphs for you.

Stop the service

You can ask the server to shutdown over the admin port also:

$ curl localhost:9900/shutdown.txt
ok

View the implementation of get() and put()

In src/main/scala, take a look at FinaglezkServiceImpl.scala. (This may have a different name, based on what you called your server.)

The base interface is specified by thrift. Additionally, we're using Twitter's async I/O framework: finagle. Finagle (and a lot of great documentation about it) is hosted here: https://github.com/twitter/finagle

Try adding some timers and counters

At the top of FinaglezkServiceImpl.scala, add:

import com.twitter.ostrich.stats.Stats

Then inside get():

Stats.incr("finaglezk.gets")

and inside put():

Stats.incr("finaglezk.puts")

Then restart your server, talk to the server via console, and check your stats:

$ curl localhost:9900/stats.txt
counters:
  Finaglezk/connects: 1
  Finaglezk/requests: 2
  Finaglezk/success: 2
  finaglezk.gets: 1
  finaglezk.puts: 1

You can also time various things that your server is doing, for example:

Stats.time("finaglezk.put.latency") {
  Thread.sleep(10) // so you can see it
  database(key) = value
}

Specs: let's add some tests

Specs is a Behavior-Driven Design framework that allows you to write semi-human-readable descriptions of how your service should behave and test that those descriptions are valid. You already have some Specs code for your project in src/test/scala/com/twitter/finaglezk/FinaglezkServiceSpec.scala. Check out the existing test and add a new one for the counter functionality we just added.

import com.twitter.ostrich.stats.Stats

...

"verify stats" in {
  val counters = Stats.getCounters
  finaglezk.put("name", "bluebird")()
  finaglezk.get("name")() mustEqual "bluebird"
  counters.getOrElse("finaglezk.gets", 1) must_==1
  counters.getOrElse("finaglezk.puts", 1) must_==1
}

TODO: add link to scala school lesson on Specs

Automatically compile and test your server when you change code

By now you've had to Ctrl-C your server and restart it to get changes to show up. This gets a little tiresome. The build tool we are using, SBT (simple build tool) has a console that you can access by just running "sbt" from the command line.

$ sbt
[info] Standard project rules 0.11.4 loaded (2011-03-18).
[warn] No .svnrepo file; no svn repo will be configured.
[info] Building project finaglezk 1.0.0-SNAPSHOT against Scala 2.8.1
[info]    using FinaglezkProject with sbt 0.7.4 and Scala 2.7.7

SBT has a wide array of features, but a useful one right now is to use the "~ test" command.

> ~ test

The tilde tells SBT to look for changes to your source files and re-execute the command when it detects a change.

TODO: add link to scala school lesson on SBT

Add an admin / dashboard page.

Add a new dependency to your project, perhaps twitter/util?

Take a tour of the logs our service is producing.

Add command-line parameters for your service.

-D foo=bar runtime.arguments.get("foo")

Storage: let's persist the data in Cassandra!

Twitter API: let's listen to the Firehose!

Twitter API: let's fetch some statuses & users & stuff.