A web application with Play, ScalaJS, ReactJS - Part I

This is the first artcle in the blog post series developing a web application based on Scala, ScalaJS, React and Play and I will look at the initial set up. At the end of this first part I want to have a minimalistic Play application that is configured as a multi-module SBT project (with only one module for now) which is deployable on Heroku and instrumented for basic monitoring.

I assume that you are familiar with git and github and already have set up git on your machine.

All code behind this part of the tutorial is available in the branch 01_Initial_Setup within the project’s github repository.

Scala, Play, Typesafe Activator, SBT and your favorite IDE

I will use the current versions of Scala (2.11.4), Play (2.3.7) and Sbt (0.13.7) for this project.


For development you should have a JDK, Scala and SBT set up on your machine. A JDK is required as an execution environment for all the required tools. Though you could just downlowd the Typesafe Activator to get started with developing applications in Scala and Play, personally I prefer a separate installation of the participating tools to have them at my fingertips when I need them.

You can download the desired Scala platform from here. Simply download the binaries for your operating system and unzip them into a directory of your choice. Make sure the bin directory of the unzipped binaries is on the search path for executables.

On Linux or OS X i tend to create a symbolic link named scala to the unzipped binaries I want to use and put that on my path. For example within my OS X environment I have unzipped scala into /opt and therefore have

drwxr-xr-x@  8 root     wheel   272 18 Dec 12:27 .
drwxr-xr-x  34 root     wheel  1224 12 Dec 10:55 ..
drwxr-xr-x   8 root     wheel   272 11 Aug 23:55 X11
drwxr-xr-x   9 root     wheel   306 13 Oct 14:20 apache-maven-3.0.5
lrwxr-xr-x   1 root     wheel    18 13 Oct 14:20 maven -> apache-maven-3.0.5
lrwxr-xr-x   1 root     wheel    12 18 Dec 12:26 scala -> scala-2.11.4
drwxrwxr-x@  6 2000     2000    204 24 Oct 01:00 scala-2.11.4
drwxr-xr-x@  5 andreas  staff   170 13 Oct 19:18 zinc-

After the successful installation and configuration you should be able to execute scala -version from the command and see something like this as a result:

$ scala -version
Scala code runner version 2.11.4 -- Copyright 2002-2013, LAMP/EPFL


Next, you can download the desired sbt version from here. I tend to use the manual installation and download the archive with the binaries for my platform and extract them into a directory of my choice. This will create a new directory named sbt which i normally change to sbt-version where version is the sbt version. This allows me again to create a symbolic link named sbt` to the renamed directory and set up my path using the symbolic link.

Now we would have something like

$ cd /opt
$ ls -al
total 24
drwxr-xr-x@ 10 root     wheel   340  3 Jan 16:36 .
drwxr-xr-x  34 root     wheel  1224 12 Dec 10:55 ..
drwxr-xr-x   8 root     wheel   272 11 Aug 23:55 X11
drwxr-xr-x   9 root     wheel   306 13 Oct 14:20 apache-maven-3.0.5
lrwxr-xr-x   1 root     wheel    18 13 Oct 14:20 maven -> apache-maven-3.0.5
lrwxr-xr-x   1 root     wheel    10  3 Jan 16:36 sbt -> sbt-0.13.7
drwxr-xr-x@  5 andreas  staff   170  3 Jan 16:36 sbt-0.13.7
lrwxr-xr-x   1 root     wheel    12 18 Dec 12:26 scala -> scala-2.11.4
drwxrwxr-x@  6 2000     2000    204 24 Oct 01:00 scala-2.11.4
drwxr-xr-x@  5 andreas  staff   170 13 Oct 19:18 zinc-

You can double check the sbt setup with sbt --version and should see something like

$ sbt --version
sbt launcher version 0.13.7

Typesafe Activator

Last not least you can download the typesafe activator. This is an application that gives you access to a ton of ready-to-go examples for the Typesafe platform. I will only use the activator to create a basic Play application later on. You can always create and explore any of the other examples to dig into a particular use case in more detail. Refer to the activator documentation to learn how to browse the examples and use them as starting points for your new application.

If you have followed the instructions to get started with the activator, you should have the activator executable on your path and executing activator ui should start the activator backend and a browser with the the activator ui.

Your favorite IDE

Personally I use IntelliJ IDEA for developing in Scala. An alternative is the Eclipse based Scala-IDE. Install the IDE of your choice and we are ready to go.

Create the initial Play application

Apparently the fastest way to get started with a new Play application is with one of the sample applications available within the activator. There are many sample applications touching quite a range of technologies. However, personally I felt that I would gain a deeper understanding if I started with the simplest template available and subsequently add the pieces I require for my application.

The example I have chosen is just-play-scala. It is a minimal Play application with no dependencies. You can either instantiate the template from the activator ui within the browser or use the activator command line.

For now I’ll stick with the command line version to create the application. Regardless which template you use you can use activator new <app-name> <template-name> to instantiate the chosen template with an arbitrary name. In my case I have used

$ activator new castillo just-play-scala

The result on the command line should look like this:

Fetching the latest list of templates...

OK, application "castillo" is being created using the "just-play-scala" template.

To run "castillo" from the command line, "cd castillo" then:
/Users/andreas/projects/play/castillo/activator run

To run the test for "castillo" from the command line, "cd castillo" then:
/Users/andreas/projects/play/castillo/activator test

To run the Activator UI for "castillo" from the command line, "cd castillo" then:
/Users/andreas/projects/play/castillo/activator ui

The activator has instantiated the template in a subdirectory <app-name>. This is a ready to run sbt project, which you can open in your IDE. I won’t go through the files that have been created, take your time to browse through them and understand what they are doing. The initial post contains some references that can help digesting the generated files sufficiently.

Running the initial application

Now you can navigate to the directory where the application has been generated and execute the application by

sbt run

This will build the application and start the Play framework running it with a listener available on port 9000:

$ sbt run
[info] Loading project definition from /Users/andreas/projects/play/castillo/project
[info] Updating {file:/Users/andreas/projects/play/castillo/project/}castillo-build...
[info] Resolving org.fusesource.jansi#jansi;1.4 ...
[info] Done updating.
[info] Set current project to castillo (in build file:/Users/andreas/projects/play/castillo/)
[info] Updating {file:/Users/andreas/projects/play/castillo/}root...
[info] Resolving org.fusesource.jansi#jansi;1.4 ...
[info] Done updating.

--- (Running the application from SBT, auto-reloading is enabled) ---

[info] play - Listening for HTTP on /0:0:0:0:0:0:0:0:9000

(Server started, use Ctrl+D to stop and go back to the console...)

You can now open a browser and navigate to http://localhost:9000 and you should see a friendly Just Play Scala in the browser window as a result. I admit it is not much of an application, but it is nice to look at and nothing that keeps the brain busy for too long. Stop the server with Ctrl-C and we start cleaning up the initial set up.

Initial git commit

Examining the generated application you will find 3 files activator, activator.bat, activator-launch-<version>.jar. As you can run the project with sbt only I tend to get rid of these files and remove them before the initial commit. Also I find it is a good practice to run sbt clean and delete the logs before the initial commit. Also review the LICENSE file that has been generated.

Now we are ready to create an initial git repository and perform the initial commit:

$ git init
Initialized empty Git repository in /Users/andreas/projects/play/castillo/.git/
$ git add .
$ git commit -m "Initial commit."
[master (root-commit) 7f42791] Initial commit.
 9 files changed, 128 insertions(+)
 create mode 100644 .gitignore
 create mode 100644 LICENSE
 create mode 100644 app/controllers/Application.scala
 create mode 100644 app/views/main.scala.html
 create mode 100644 build.sbt
 create mode 100644 conf/application.conf
 create mode 100644 conf/routes
 create mode 100644 project/build.properties
 create mode 100644 project/plugins.sbt
$ git status
On branch master
nothing to commit, working directory clean

After the initial commit we create a repository on github and add it to our project as a remote repository. The code for the application lives at https://github.com/CastilloSanRafael/castillo. To add the remote repository and push the initial commit:

$ git remote add origin ssh://git@github.com/CastilloSanRafael/castillo.git
$ git push origin master
Counting objects: 16, done.
Delta compression using up to 4 threads.
Compressing objects: 100% (14/14), done.
Writing objects: 100% (16/16), 2.71 KiB | 0 bytes/s, done.
Total 16 (delta 0), reused 0 (delta 0)
To ssh://git@github.com/CastilloSanRafael/castillo.git
 * [new branch]      master -> master
$ git branch --set-upstream-to=origin/master
Branch master set up to track remote branch master from origin.
$ git checkout -b 01_InitialSetup
Switched to a new branch '01_InitialSetup'
$ git push origin --all
Total 0 (delta 0), reused 0 (delta 0)
To ssh://git@github.com/CastilloSanRafael/castillo.git
 * [new branch]      01_InitialSetup -> 01_InitialSetup

Deploy the application to Heroku

Though the application we have is not much to look at I have decided to get the deployment and some basic application monitoring out of the way right from the beginning. There are some hosting alternatives for Play applications and I have decided to go with Heroku based articles and recommendations. For each application you deploy to Heroku you get 750 instance hours. This basically that Heroku deployment is free as long as you use a single instance only, which is perfect for development. Later on the application can be scaled to multiple instances, which would be more than 750 instance hours already with 2 instances.

To get started with Heroku and Play you can follow the Heroku Scala tutorial. Basically you have to

  • Install the heroku toolbelt, a simple command line utility to interact with Heroku
  • Add a Heroku repository as additional remote repository
  • Push the code to Heroku
  • Provide additional configuration if required

After you have installed the heroku toolbelt for your platform, you can use heroku login to log into your heroku account; then you simply use heroku create to create the heroku git repository and add it as a remote repository to the project. This will add an additional remote repository to the project. Every time the master branch is pushed to that repository, the application will be rebuilt and started.

$ heroku login
Enter your Heroku credentials.
Email: andreas@wayofquality.de
Password (typing will be hidden): 
Authentication successful.
$ heroku create
Your version of git is 1.9.3. Which has serious security vulnerabilities.
More information here: https://blog.heroku.com/archives/2014/12/23/update_your_git_clients_on_windows_and_os_x
Creating stormy-crag-3594... done, stack is cedar-14
https://stormy-crag-3594.herokuapp.com/ | https://git.heroku.com/stormy-crag-3594.git
Git remote heroku added
$ git push heroku master
Counting objects: 16, done.
Delta compression using up to 4 threads.
Compressing objects: 100% (14/14), done.
Writing objects: 100% (16/16), 2.71 KiB | 0 bytes/s, done.
Total 16 (delta 0), reused 0 (delta 0)
remote: Compressing source files... done.
remote: Building source:
remote: -----> Play 2.x - Scala app detected
remote: -----> Installing OpenJDK 1.8... done
remote: -----> Downloading SBT... done
remote: -----> Priming Ivy cache (Scala-2.10, Play-2.3)... done
remote: -----> Running: sbt update
remote:        OpenJDK 64-Bit Server VM warning: ignoring option MaxPermSize=512M; support was removed in 8.0
remote:        [info] Loading global plugins from /tmp/scala_buildpack_build_dir/.sbt_home/plugins
remote:        [info] Updating {file:/tmp/scala_buildpack_build_dir/.sbt_home/plugins/}global-plugins...
remote:        [info] Resolving org.scala-lang#scala-library;2.10.4 ...
remote:        [info] Resolving org.scala-sbt#sbt;0.13.5 ...

... Many more lines of build output 

remote: -----> Running: sbt compile stage
remote:        OpenJDK 64-Bit Server VM warning: ignoring option MaxPermSize=512M; support was removed in 8.0
remote:        [info] Loading global plugins from /tmp/scala_buildpack_build_dir/.sbt_home/plugins
remote:        [info] Loading project definition from /tmp/scala_buildpack_build_dir/project
remote:        [info] Set current project to castillo (in build file:/tmp/scala_buildpack_build_dir/)
remote:        [info] Compiling 4 Scala sources and 1 Java source to /tmp/scala_buildpack_build_dir/target/scala-2.10/classes...
remote:        [success] Total time: 24 s, completed Jan 4, 2015 5:22:51 PM
remote:        [info] Wrote /tmp/scala_buildpack_build_dir/target/scala-2.10/castillo_2.10-1.0-SNAPSHOT.pom
remote:        [info] Packaging /tmp/scala_buildpack_build_dir/target/castillo-1.0-SNAPSHOT-assets.jar ...
remote:        [info] Packaging /tmp/scala_buildpack_build_dir/target/scala-2.10/castillo_2.10-1.0-SNAPSHOT.jar ...
remote:        [info] Done packaging.
remote:        [info] Done packaging.
remote:        [success] Total time: 1 s, completed Jan 4, 2015 5:22:51 PM
remote: -----> Dropping ivy cache from the slug
remote: -----> Dropping sbt boot dir from the slug
remote: -----> Dropping compilation artifacts from the slug
remote: -----> Discovering process types
remote:        Procfile declares types            -> (none)
remote:        Default types for Play 2.x - Scala -> web
remote: -----> Compressing... done, 71.8MB
remote: -----> Launching... done, v6
remote:        https://stormy-crag-3594.herokuapp.com/ deployed to Heroku
remote: Verifying deploy... done.
To https://git.heroku.com/stormy-crag-3594.git
 * [new branch]      master -> master

This last couple of lines show that the Play application has been built and published. It is available at https://stormy-crag-3594.herokuapp.com. Examining the build output we see that we are using the wrong versions on the Heroku instance: Scala 2.10 rather than 2.11.4 and Play 2.3.4 rather than 2.3.7.

Studying some of the example projects it seems that creating a Scala build file is the way to go for a multi module project. Though we have only one module so far we will start by creating a file CastilloBuild.scala within the project’s project folder:

 1 import com.typesafe.sbt.packager.universal.UniversalKeys
 2 import play._
 3 import sbt._
 4 import Keys._
 6 object CastilloBuild extends Build with UniversalKeys {
 8   /**
 9    * Define the root project as a Play application.
10    */
11   lazy val root =
12     project.in(file("."))
13     .settings(commonSettings:_*)
14     .enablePlugins(PlayScala)
16   /**
17    * The setting that will be applied to all sub projects
18    */
19   lazy val commonSettings = Seq(
20     organization := "de.woq",
21     version := "1.0-SNAPSHOT",
22     name := "castillo",
23     scalaVersion := "2.11.4"
24   )
25 }

After creating that file we can get rid of the file build.sbt in the root folder of the project. To finish the cleanup we make sure that the sbt version is 0.13.7 in the file project/build.properties. Finally we set the desired version of the Play framework in the file project/plugins.sbt.

On Heroku we want to make sure that we execute the application on top of JDK 7, so we create a system.properties in the root directory of the project setting the java runtime like this:


To double check the changes we can push them to heroku and wait until the application has been rebuilt. The application should be rebuilt and published and we should be able to navigate to the project’s homepage on heroku again.

Note: Heroku uses the OpenJDK by default. Later on I will investigate how to use the Oracle JSK instead. It seems there is a rather old thread on this. It should be possible to use a heroku buildpack based on the Oracle JDK later on.

Change the application secret for deployment on Heroku

The application has been generated with a play application secret that should only be used for the development server. In production this should be a secret key. Therefore we change the file conf/application.conf, so that the application key is


Then we set the application secret on the heroku application using the heroku client:

$ heroku config:add APP_SECRET=MySuperSecret
Setting config vars and restarting stormy-crag-3594... done, v13
APP_SECRET: MySuperSecret

As you can see heroku has set the config value and restarted the application.

Instrumentation to monitor the logs

Now we have an initial application up and running with the correct versions and we want to set up a basic monitoring for the logs. We can achieve this by selecting an appropriate addon for our heroku application from the Heroku AddOn Overview. I have selected the Papertrail add-on, but I would love to hear about other plugins that perform the same task.

To add the papertrail add-on to the application, we use the heroku client from a command line within the project’s root folder:

$ heroku addons:add papertrail
Adding papertrail on stormy-crag-3594... done, v11 (free)
Welcome to Papertrail. Questions and ideas are welcome (support@papertrailapp.com). Happy logging!
Use `heroku addons:docs papertrail` to view documentation.

Afterwards we can see the papertrail add-on from the application’s dashboard on heroku:

The application dashboard

From here we can navigate to the add-on itself and will see the recorded log events:

Some application logs

Instrumentation for basic application monitoring

Next we will add some basic application monitoring in order to monitor the application’s health and response times. The add-on I have chosen is NewRelic. Again I would love to hear pro’s and con’s for other plugins.

Adding new relic support to the application is a bit more involved - we have to:

  • Set up NewRelic as an addon for the application.
  • Add the NewRelic agent as a dependency to the project
  • Change the Heroku configuration to be aware of the agent on startup

First we add NewRelic to the application:

$ heroku addons:add newrelic
Adding newrelic on stormy-crag-3594... done, v12 (free)
Use `heroku addons:docs newrelic` to view documentation.

From the application’s heroku dashboard we navigate to the NewRelic add-on and need to agree to the license agreement. You can double check the NewRelic settings for your application with the heroku client from a command line within the projects root directory:

$ heroku config
=== stormy-crag-3594 Config Vars
JAVA_OPTS:             -Xss512k -XX:+UseCompressedOops
NEW_RELIC_LICENSE_KEY: <<My super secret license key>>
NEW_RELIC_LOG:         stdout
PAPERTRAIL_API_TOKEN:  <My secret token>
PATH:                  .jdk/bin:.sbt_home/bin:/usr/local/bin:/usr/bin:/bin
REPO:                  /app/.sbt_home/.ivy2/cache
SBT_OPTS:              -Xmx384m -Xss512k -XX:+UseCompressedOops

Now, first of all we need to add a library dependency for the newrelic agent to our project, so that it will be included in the packaged application. Essentially, this is done within the projects build file.

Next, we need to set up a heroku Procfile and fine tune the Java options. These changes will take enable the NewRelic agent within the Play application.

The Procfile lives in the project’s root directory and looks like this:

web: target/universal/stage/bin/castillo -Dhttp.port=${PORT} -Dnewrelic.config.license_key=${NEW_RELIC_LICENSE_KEY}

Here I only appended the reference to the newrelic license key which is configured uniquely for my application. Having the license key as a reference within the Procfile avoids having it in clear text in the newrelic config file.

Next we modify the Java options and add the newrelic agent reference. Since we have added the agent jar as a dependency, it will end up in the play application’s lib directory, so we simply add


to the Java options. Make sure to look up the current value with heroku config:get JAVA_OPTS and then run

heroku config:set JAVA_OPTS="<old value goes here> -javaagent:target/universal/stage/lib/com.newrelic.agent.java.newrelic-agent-3.12.1.jar"

According to the newrelic documentation this should get us going, but reviewing the logs after the application has been restarted the agent complains about a missing newrelic configuration file. It turns out that we can download a template for that file from the application’s newrelic dashboard when we look at the Ruby configuration. Simply download newrelic.yml and stick it in the application’s root directory.

Within newrelic.yml we comment out the license key and switch it to something else than the real value. Also we adjust the app_name, so that it has a meaningful name within newrelic’s dashboards.

After these changes we push again to heroku master and wait for the application to be restarted. We can use the logging dashboard to inspect the logs and make sure that the agent has been started correctly.

Now we can navigate again to the applications entry page.

Note that the application takes some time to load when you haven’t used it for a while and have configured only a single heroku instance. This should be fine for development though.

After a short while the traffic and response times should show up on the application’s NewRelic dashboard on Heroku:

Some application traffic

Refactor to a basic multi-module project

Now we basically have something like a hello world application deployed on Heroku with some nice dashboards for log and application monitoring. The final step for the first part of this series is to refactor the build file, so that the project is already geared towards supporting multiple modules.

We have only one module so far, which is the play application itself. The code for this application lives within app, conf and public. Essentially we are going to create a subdirectory server and move those directories to that directory. Then we need to make the appropriate changes to our build file.

$ mkdir server
$ git add server
$ git mv app/ server/
$ git mv conf/ server
$ git mv public/ server/
$ git status
# On branch 01_InitialSetup
# Changes to be committed:
#   (use "git reset HEAD <file>..." to unstage)
#	renamed:    app/controllers/Application.scala -> server/app/controllers/Application.scala
#	renamed:    app/views/main.scala.html -> server/app/views/main.scala.html
#	renamed:    conf/application.conf -> server/conf/application.conf
#	renamed:    conf/routes -> server/conf/routes

Within the build file we reflect the changes by renaming the root project to server and change the directory from "." to "server". Further we add a new root project aggregating the on and only sub project. Some more changes have been done more or less for cosmetic reasons. Here are all the changes for the build file.

For Heroku we need to reflect the new subdirectory within the Procfile

web: server/target/universal/stage/bin/castillo-server -Dhttp.port=${PORT} -Dnewrelic.config.license_key=${NEW_RELIC_LICENSE_KEY}

and also within the JAVA_OPTS

heroku config:set JAVA_OPTS="-Xss512k -XX:+UseCompressedOops -javaagent:server/target/universal/stage/lib/com.newrelic.agent.java.newrelic-agent-3.12.1.jar"

Then we can push the changes to heroku. After the application has been rebuilt and published we should be able to navigate to the applications entry page as before.

After deplyment I got a Heroku error message about the slug size:

remote: -----> Compressing... 
remote:  !   Compiled slug size: 472.2MB is too large (max is 300MB).
remote:  !   See: http://devcenter.heroku.com/articles/slug-size
remote:  !     Push failed: slug archive could not be created
remote:  !     If the problem persists, see http://help.heroku.com and provide Request ID bee7f883-8414-4160-b398-b502a04de312.
remote: Verifying deploy...
remote: !	Push rejected to stormy-crag-3594.

Referring to the Heroku documentation we need to reduce the slug size of the deployed application and the first measure is to add the sbt-native-packager to the application’s list of sbt plugins in project/plugins.sbt:

resolvers += "Typesafe repository" at "http://repo.typesafe.com/typesafe/releases/"

addSbtPlugin("com.typesafe.play" % "sbt-plugin" % "2.3.7")

addSbtPlugin("com.typesafe.sbt" % "sbt-native-packager" % "0.8.0-RC2")

Once the plugin is added, the application can be deployed and works as before.

Next steps

Now we have a simplistic project up and running on Heroku and have already prepared to enhance the project with additional modules. The build file starts to take shape and we should have the basic configuration files for monitoring the application in place.

Next time we will add the first business object and a minimal REST interface to interact with it on the server.

In a subsequent post we will reuse the business object on the client side in a very simple ReactJS UI.

Any comments / suggestions are very much appreciated.