Wednesday, February 29, 2012

Neo4J with Scala Play! 2.0 on Heroku (Part 9) :: Final


This post is a continuation of this post (which started there), which is the last part of a blog suite that aims the use of Neo4j and Play2.0 together on Heroku.

What have been accomplished so far:

  • install Play 2.0
  • install Neo4J
  • use Dispatch
  • create model
  • create persistence service in Neo4J
  • create views and controllers
Ok, where almost done. Let's see how to deploy the whole app on Heroku.

Heroku, here I come

But wait, who're you?

Heroku is simply one of the best cloud players of the moment, I won't talk too much about it, because i'd have to talk a lot otherwise.

But here are some very interesting features and paradigms followed by Heroku.

Process Centric

Where almost all other cloud providers are binding their services to server instances, CPU flop count, memory usages, and other similar metrics, it is a fact that their aren't easily forecastable and hard to track in development phases (even if I encouraged to do it, though).

Heroku comes with a much more easy concept, that is, Web Dynos. A Web Dynos is simply a process that can handle requests. So, what if the requests are too numerous? Just add Dynos. Note that Dynos are existsing for background process, one Dyno by worker.

Costs are very simple too, you have one free Dyno by month, and the rest is billed at low cost by hour.

Thanks for simplicity.

Remote CLI

We've just ask how to handle more requests in an efficient way, and answered by adding dynos.

So far so good, but how? That's where comes the Heroku remote CLI that is able to operate remotely on a deployed application behavior.

Thus, adding a dyno is doing that in console : $> heroku dynos 1

Now, alerts on performance are quickly resolved.

Thanks for rapidity.

Continuous Deployment

The paradigm followed by Heroku to deploy their app are based on Continuous Deployment.

Having that, you app should define how you app must be deployed using their Procfile.

And it will be deployed automatically when the sources are pushed to the Git repo that is created for each application.

This ensure you to at any time be able to retrieve the sources related to the running instance (for example).

Thanks for debugging ease.


What to say? A good sdk to create add-ons, a good architecture and service level. It makes a pleiade of powerful add-ons including Neo4J running instances.

Thanks to be open.

Can I Play! with Heroku?

Of course, you can!

Actually, Heroku has already integrated Play! starting with its first version, and has also added the scala support some time ago.

And finally the Play 2.0 wiki is explaining how to do...

Ok, let's Go then.

Getting started

First of all, you must have been registered too Heroku. Hopefully, it's free and fast. So go on, and create your account here

Having your account, you can now install the Heroku toolkit belt. This will gives you acces to your Heroku CLI that can manage your account, apps, and app configuration.

When you're done with the installation, you just have to login using the console command: $> heroku login

Play! app side

What is needed for your app is to have a Git repo and to contain a Heroku process description file.
Since everything is already explain there, I won't go into deep details.

Create Heroku app

Since we are using Play! and scala, we need a JVM, that stack at Heroku is called Cedar.

So, to create your app, open a shell and do the following:
heroku create my-playing-app-with-neo4j --stack cedar

Now, you have an up and running environment to setup and deploy your application. And the application will be named my-playing-app-with-neo4j.

Neo4J add-on

Ok, but I've to use a Neo4J database, not embedded (too heavy for a cloud). Do I have to install it somewhere and host it myself. Na!

Neo4J's team is actually working on an integration in the Heroku platform, and a beta test add-on is available at the time writing.

That says that to have a running database that we can use, we just have to open a shell (in our app folder) and drop the following command: heroku addons:add neo4j 

You don't believe it, huh?

Since you'll need to retrieve the database url and credentials, either you go to the Heroku site and...
Na, just keep your shell and do: heroku addons:open neo4j 

Ta da!

App update

In my previous post, for the sake of simplicity I left the Neo4J database hard coded to localhost:7474.

But now, we have to update this to use our deployed Neo4J instance and credentials.

We should have (must) define an application configuration property for such paramater, but It is not what I want to illustrate here so let's keep it simple and hard coded.

But we have to add something to the Neo4J's Dispatch url, the credentials. For that we just have to do the following:

SSH key

Just a note, to remember you to add your ssh key to Heroku. This is simply accomplished (after you've have created 'em) using the CLI: $> heroku keys:add

Beginning to love this CLI, no?


This is the Heroku configuration file that tells the continuous deployer (if I can say) how the application will be deployed and are its needs.

This file is located at the root of the Play's application folder and only contains one line:
web: target/start -Dhttp.port=${PORT} ${JAVA_OPTS}

This simple line tells that we need a web process for the staging application located under target/start
Actually, this folder will contains the staging Play! application after Heroku will run sbt clean compile stage on it.

Aaaaand Deploy! (push)

Getting closer to the end!

After having added all the necessary sources to the local git repo for your app, (including last update and the Procfile), we can now commit everything and push it to the git repo that Heroku holds for our application.

Actually, when created the Heroku app, the CLI has updated the git local configuration to add the related remote repo called heroku.

So, the only thing that left to do is to push: $> git push heroku master
To test if it is ok: $> heroku ps. This will display the proceses running on Heroku.

If the process is shown, let's open the application in our default brower (leave your mouse alone and...):  $> heroku open.

I hope that I didn't made too many mistakes and you are now able to see your application running and using Neo4J.

At least, here is the one I succeed to deploy:
I've also shared this app on Heroku's GenSen that is meant to share project template on Heroku.

Now, you should love the CLI, but also Heroku, and Neo4J and Play! 2.0 and Scala and Dispatch and arbor.js and...

Thanks for reading, if someone do have ^^.

No comments:

Post a Comment