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Play Framework 2 Scala

Play Framework 2 Scala

Overview

Clever Cloud supports Play! 2 applications natively. The following guide explains how to set up your application to run on Clever Cloud.

Create an application on Clever Cloud

With the web console

Refer to Quickstart for more details on application creation via the console.

With the Clever Tools CLI

  1. Make sure you have clever-tools installed locally or follow our CLI getting started guide.
  2. In your code folder, do clever create --type <type> <app-name> --region <zone> --org <org> where :
    1. type is the type of technology you rely on
    2. app-name the name you want for your application,
    3. zone deployment zone (par for Paris and mtl for Montreal)
    4. org the organization ID the application will be created under.

Refer to clever create for more details on application creation with Clever Tools.

Setting up environment variables on Clever Cloud

With the Clever Cloud console

  1. Go to the Clever Cloud console, and find the app you want to fine tune under it’s organization.
  2. Find the Environment variables menu and select it.
  3. In this menu, you will see a form with VARIABLE_NAME and variable value fields.
  4. Fill them with the desired values then select Add.
  5. Don’t forget to “Update Changes” at the end of the menu.

With the Clever Tools CLI

  1. Make sure you have clever-tools installed locally. Refer to our CLI getting started.
  2. In your code folder, do clever env set <variable-name> <variable-value>

Refer to environment variables reference for more details on available environment variables on Clever Cloud.

You can of course create custom ones with the interface we just demonstrated, they will be available for your application.

Configure your Scala + Play! 2 application

Mandatory configuration

  • Starting from Play 2.4, your application needs Java 8 to run. Please read select java version for more information.

Play! 2 applications use sbt. Please have a look at deploy scala apps for a complete documentation on sbt deployment options.

Generate application secret

To deploy a Play! application you have to set a secret in your conf/application.conf the environment variable name depends on your Play2! version:

  • 2.6.x: play.http.secret.key=${?APPLICATION_SECRET}, to generate secret use sbt playGenerateSecret;
  • 2.4.x -> 2.5.x: play.crypto.secret=${?APPLICATION_SECRET} -> sbt playGenerateSecret;
  • 2.3.x: application.secret=${?APPLICATION_SECRET} -> sbt play-generate-secret.

Then, in your Clever Cloud application define APPLICATION_SECRET environment variable with the generated value.

Custom config file

If you don’t want to use the default conf/application.conf configuration file, you can use the SBT_DEPLOY_GOAL environment variable SBT_DEPLOY_GOAL=-Dconfig.resource=clevercloud.conf

HTTPS support

HTTPS is handled by Clever Cloud ahead of your application, your application retrieves the traffic in plain http.

If you want to redirect HTTP traffic to HTTPS, please have a look at How to Redirect to HTTPS With Play 2.4.

HTTP support with Play! 2.x < 2.4

To be able to use request.secure, you have to add trustxforwarded=true in application.conf.

Multi-module project

If you have a single repository with multiple modules, then you can specify which module to run with CC_SBT_TARGET_DIR environment variable.

For instance, if your Sbt project contains a shared and play module and you want to execute the play module, then add CC_SBT_TARGET_DIR=play environment variable.

Monitor your application with New Relic

You can use New Relic to monitor your application on Clever Cloud.

Please refer to our New Relic documentation to configure it for your application.

Environment injection

Clever Cloud injects environment variables from your application settings as mentioned in setting up environment variables and is also injecting in your application production environment, those from your linked add-ons.

Custom build configurations

On Clever Cloud you can define some build configuration: like the app folder to deploy or the path to validate your application deployment is ready To do that follow the documentation here and add the environement variable you need.

To access the environment variables from your code, you need to add my.option=${MY_VARIABLE} in your application.conf file, and then use the configuration item my.option in your application. e.g %clevercloud.db.url="jdbc:mysql://"${MYSQL_ADDON_HOST}"/"${MYSQL_ADDON_DB}. You can also use the System.getenv("MY_VARIABLE") method. Be aware that it can return null.

Git Deployment on Clever Cloud

You need Git on your computer to deploy via this tool. Here is the official website of Git to get more information: git-scm.com

Setting up your remotes

  1. The “Information” page of your app gives you your Git deployment URL, it looks like this:

    1. git+ssh://git@push.clever-cloud.com/<your_app_id>.git
    2. Copy it in your clipboard

  2. Locally, under your code folder, type in git init to set up a new git repository or skip this step if you already have one

  3. Add the deploy URL with git remote add <name> <your-git-deployment-url>

  4. Add your files via git add <files path> and commit them via git commit -m <your commit message>

  5. Now push your application on Clever Cloud with git push <name> master

Refer to git deployments for more details.

Linking a database or any other add-on to your application

By linking an application to an add-on, the application has the add-on environment variables in its own environment by default.

On add-on creation

Many add-ons do exist on Clever Cloud: refer to the full list and check add-ons dedicated pages for full instructions.

During add-on creation, an Applications screen appears, with a list of your applications. You can toggle the button to Link and click next. If you finish the process of add-on creation, the application is automatically linked to it.

Add-on already exists

In the Clever Cloud console, under the Service Dependencies menu of your application, you can use the Link add-ons dropdown menu to select the name of the add-on you want to link and use the add button to finish the process.

You can also link another application from the same page in the Clever Cloud console, using the Link applications dropdown menu.

Known problems with Play! 2

sbt-plugin unresolved dependency error

If your project fails with the error sbt.ResolveException: unresolved dependency: play#sbt-plugin;2.0: not found this is because some versions of Play2 try to retrieve a nonexistent version of “sbt-plugin” which is required by the framework. You have two options to fix this problem:

  • You can set the “play.version” environment variable in the /clevercloud/sbt.json file. For example, for Play 2.0.4:
{
  "deploy": {
    "goal": "-Dplay.version=2.0.4"
  }
}
  • You can modify plugins.sbt in the project folder of your app like the following:
// Comment to get more information during initialization
logLevel := Level.Warn

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

// Use the Play sbt plugin for Play projects
addSbtPlugin("play" % "sbt-plugin" % "2.0.4") // The important part of the configuration

Both alternatives effectively fulfill the task at hand; you are free to select the one that best suits your preference.

More info on playframework.com.

Bad root server path error

The error occurs when we cannot find a bin to execute your project.

Failed to acquire connection: Too many connections

You may run into this error during deployments:

[error] c.j.b.h.AbstractConnectionHook - Failed to acquire connection to jdbc:<address> Sleeping for 1000ms and trying again. Attempts left: 10. Exception: null.Message:FATAL: too many connections for role "<user>"

By default, Play! opens a pool of 10 connections, which is more than the connection limit allowed by DEV database plans. During a no-downtime deployment, there are at least two instances of the application running in parallel, so it’s 20 connections.

To avoid connection exhaustion, you should limit your pool at half the number of available connections (if you have horizontal scaling enabled, adjust accordingly).

# conf/application.conf

db.default.partitionCount=2
db.default.maxConnectionsPerPartition=5
db.default.minConnectionsPerPartition=5

More configuration

Need more configuration? To run a script at the end of your deployment? To add your private SSH key to access private dependencies?

Go check the Common configuration page.

You may want to have an advanced usage of your application, in which case we recommend you to read the Administrate documentation section.

If you can’t find something or have a specific need like using a non supported version of a particular software, please reach out to the support.

Enable health check during deployment

The healthcheck allows you to limit downtimes. Indeed, you can provide Clever Cloud with paths to check. If these paths return something other than 200, the deployment will fail.

Add one (or several) environment variable as such:

CC_HEALTH_CHECK_PATH=/my/awesome/path

Or

CC_HEALTH_CHECK_PATH_0=/my/awesome/path
CC_HEALTH_CHECK_PATH_1=/my/other/path

The deployment process checks all paths. All of them must reply with a 200 OK response code.

By default, when no environment variable (for ex: APP_HOME) is defined, the monitoring checks your repository root path /.

Example

Using the path listed above, below are the expected logs:

Response from GET /my/awesome/path is 200
Response from GET /my/other/path is 500
Health check failed:
- GET /my/other/path returned 500.
If the deployment fails after this message, please update your configuration and redeploy.

In this example, the first path is OK, but the second one failed. This gives you a hint on what failed in your application.

Best practice for healthcheck endpoints

To make the most of a healthcheck endpoint, have it check your critical dependencies. For example:

  • execute SELECT 1 + 1; on your database
  • retrieve a specific Cellar file
  • ping a specific IP through a VPN
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