Getting Started on Heroku Fir with Scala and Play

Introduction

Complete this tutorial to deploy a sample Scala app to Heroku Private Spaces on the Fir generation of the platform. To deploy the app to the Common Runtime or Cedar Private Spaces, follow this guide instead.

The tutorial assumes that you have:

• A verified Heroku Account
• An existing Fir Private Space
• A team admin or member role that has the app creation permission on the space.
• An SSH key added to your Heroku account
• OpenJDK 17 (or newer) installed locally
• sbt installed
• Postgres installed locally

Set Up

Install the Heroku Command Line Interface (CLI). Use the CLI to manage and scale your app, provision add-ons, view your logs, and run your app locally.

Download and run the installer for your platform:

After installation, you can use the heroku command from your command shell.

To log in to the Heroku CLI, use the heroku login command:

$ heroku login
heroku: Press any key to open up the browser to login or q to exit:
Opening browser to https://cli-auth.heroku.com/auth/cli/browser/***
heroku: Waiting for login...
Logging in... done
Logged in as me@example.com

This command opens your web browser to the Heroku login page. If your browser is already logged in to Heroku, click the Log In button on the page.

This authentication is required for the heroku and git commands to work correctly.

If you have any problems installing or using the Heroku CLI, see the main Heroku CLI article for advice and troubleshooting steps.

Clone the Sample App

Clone the sample application to get a local version of the code. Execute these commands in your local command shell or terminal:

$ git clone https://github.com/heroku/scala-getting-started
$ cd scala-getting-started

You now have a functioning Git repository that contains a simple application. It includes a build.sbt file, which is used by sbt, a Scala build tool.

Define a Procfile

Use a Procfile, a text file in the root directory of your application, to explicitly declare what command to execute to start your app.

The Procfile in the example app looks like this:

web: target/universal/stage/bin/scala-getting-started -Dhttp.port=${PORT}

This Procfile declares a single process type, web, and the command needed to run it. The name web is important here. It declares that this process type is attached to Heroku’s HTTP routing stack and receives web traffic when deployed.

A Procfile can contain additional process types. For example, you can declare a background worker process that processes items off a queue.

Create Your App in a Fir Space

 

Create an app on Heroku to prepare the platform to receive your source code by replacing <space-name> with the name of your Fir space in the command below:

$ heroku create --space <space-name>
Creating app in space <space name>...
Creating app in space <space name>... done, morning-hollows-66944
http://morning-hollows-66944-d74ffbce4462.herokuapp.com/ | https://git.heroku.com/morning-hollows-66944.git

When you create an app, a Git remote called heroku also gets created and associated with your local Git repository. Git remotes are versions of your repository that live on other servers. You deploy your app by pushing its code to that special Heroku-hosted remote associated with your app.

Heroku generates a random name for your app, in this case, morning-hollows-66944. You can specify your own app name.

Provision a Database

The sample app requires a database. Provision a Heroku Postgres database, an add-on available through the Elements Marketplace. Add-ons are cloud services that provide out-of-the-box additional services for your application, such as logging, monitoring, databases, and more.

$ heroku addons:create heroku-postgresql:essential-0
Creating heroku-postgresql:essential-0 on morning-hollows-66944...
Creating heroku-postgresql:essential-0 on morning-hollows-66944... ~$0.007/hour (max $5/month)
Database should be available soon
postgresql-animated-10652 is being created in the background. The app will restart when complete...
Use heroku addons:info postgresql-animated-10652 to check creation progress
Use heroku addons:docs heroku-postgresql to view documentation

You can wait for the database to provision by running this command:

$ heroku pg:wait
Waiting for database postgresql-animated-10652... Provisioning
Waiting for database postgresql-animated-10652... Available

After that command exits, your Heroku app can access the Postgres database. The DATABASE_URL environment variable stores your credentials. For applications that use the JVM an additional environment variable JDBC_DATABASE_URL is available. It contains a JDBC compatible connection string. You can see all the add-ons provisioned with the addons command:

$ heroku addons

 Add-on                                        Plan        Price        Max price State
 ───────────────────────────────────────────── ─────────── ──────────── ───────── ───────
 heroku-postgresql (postgresql-animated-10652) essential-0 ~$0.007/hour $5/month  created
  └─ as DATABASE

The table above shows add-ons and the attachments to the current app (morning-hollows-66944) or other apps.

Deploy the App

Deploy your code. This command pushes the main branch of the sample repo to your heroku remote, which then deploys to Heroku:

$ git push heroku main
remote: Updated 28 paths from b8cbe02
remote: Compressing source files... done.
remote: Building source:
remote: Extracting source
remote: Image with name "morning-hollows-66944/builds" not found
remote: 3 of 4 buildpacks participating
remote: heroku/jvm      6.0.3
remote: heroku/sbt      6.0.3
remote: heroku/procfile 3.1.2
remote:
remote: [Installing OpenJDK 17.0.12]
remote:
remote: [Building Scala project]
remote: Running: sbt compile stage
remote: Downloading sbt launcher for 1.7.2:
remote:   From  https://repo1.maven.org/maven2/org/scala-sbt/sbt-launch/1.7.2/sbt-launch-1.7.2.jar
remote:     To  /layers/heroku_sbt/sbt-extras/launchers/1.7.2/sbt-launch.jar
remote: Downloading sbt launcher 1.7.2 md5 hash:
remote:   From  https://repo1.maven.org/maven2/org/scala-sbt/sbt-launch/1.7.2/sbt-launch-1.7.2.jar.md5
remote:     To  /layers/heroku_sbt/sbt-extras/launchers/1.7.2/sbt-launch.jar.md5
remote: /layers/heroku_sbt/sbt-extras/launchers/1.7.2/sbt-launch.jar: OK
remote: Picked up JAVA_TOOL_OPTIONS: -Dfile.encoding=UTF-8
remote: [info] [launcher] getting org.scala-sbt sbt 1.7.2  (this may take some time)...
remote: [info] [launcher] getting Scala 2.12.16 (for sbt)...
remote: [info] welcome to sbt 1.7.2 (Azul Systems, Inc. Java 17.0.12)
remote: [info] loading global plugins from /layers/heroku_sbt/sbt-global/plugins
remote: [info] compiling 1 Scala source to /layers/heroku_sbt/sbt-global/plugins/target/scala-2.12/sbt-1.0/classes ...
remote: [info] Non-compiled module 'compiler-bridge_2.12' for Scala 2.12.16. Compiling...
remote: [info]   Compilation completed in 12.161s.
remote: [info] done compiling
remote: [info] loading settings for project workspace-build from plugins.sbt ...
remote: [info] loading project definition from /workspace/project
remote: [info] loading settings for project root from build.sbt ...
remote: [info]   __              __
remote: [info]   \ \     ____   / /____ _ __  __
remote: [info]    \ \   / __ \ / // __ `// / / /
remote: [info]    / /  / /_/ // // /_/ // /_/ /
remote: [info]   /_/  / .___//_/ \__,_/ \__, /
remote: [info]       /_/               /____/
remote: [info]
remote: [info] Version 2.8.19 running Java 17.0.12
remote: [info]
remote: [info] Play is run entirely by the community. Please consider contributing and/or donating:
remote: [info] https://www.playframework.com/sponsors
remote: [info]
remote: [info] Running Play on Java 17 is experimental. Tweaks are necessary:
remote: [info] https://github.com/playframework/playframework/releases/2.8.15
remote: [info]
remote: [info] compiling 8 Scala sources and 1 Java source to /workspace/target/scala-2.13/classes ...
remote: [info] Non-compiled module 'compiler-bridge_2.13' for Scala 2.13.10. Compiling...
remote: [info]   Compilation completed in 11.698s.
remote: [info] done compiling
remote: [success] Total time: 18 s, completed Nov 28, 2024, 4:21:48 PM
remote: [info] Wrote /workspace/target/scala-2.13/scala-getting-started_2.13-1.0-SNAPSHOT.pom
remote: [success] Total time: 1 s, completed Nov 28, 2024, 4:21:49 PM
remote:
remote: [Discovering process types]
remote: Procfile declares types -> web
remote: Adding layer 'heroku/jvm:openjdk'
remote: Adding layer 'heroku/jvm:runtime'
remote: Adding layer 'buildpacksio/lifecycle:launch.sbom'
remote: Added 1/1 app layer(s)
remote: Adding layer 'buildpacksio/lifecycle:launcher'
remote: Adding layer 'buildpacksio/lifecycle:config'
remote: Adding layer 'buildpacksio/lifecycle:process-types'
remote: Adding label 'io.buildpacks.lifecycle.metadata'
remote: Adding label 'io.buildpacks.build.metadata'
remote: Adding label 'io.buildpacks.project.metadata'
remote: Setting default process type 'web'
remote: Saving morning-hollows-66944/builds...
remote: *** Images (sha256:ee9a97c1bc214ff5714b27d56ee3eb1381d07cc9f9eafcc1f3a7ea9642b2baf0):
remote:       morning-hollows-66944/builds:72f3de8e-8e4c-424c-b33b-9310d85c5e37
remote: Adding cache layer 'heroku/jvm:openjdk'
remote: Adding cache layer 'heroku/sbt:coursier-home'
remote: Adding cache layer 'heroku/sbt:ivy-home'
remote: Adding cache layer 'heroku/sbt:sbt-boot'
remote: Adding cache layer 'heroku/sbt:sbt-extras'
remote: Uploading cache
remote: Launching...
remote: https://morning-hollows-66944-d74ffbce4462.herokuapp.com/ deployed to Heroku
remote: Verifying deploy... done.
To https://git.heroku.com/morning-hollows-66944.git
 * [new branch]      main -> main

The app is now deployed. The default dyno size for Fir Private Spaces is 1X-Classic.

Visit the app at the URL shown in the logs. As a shortcut, you can also open the website as follows:

$ heroku open

View Logs

Heroku treats logs as streams of time-ordered events, aggregated from the output streams of all your app and Heroku components. Heroku provides a single stream for all events. View information about your running app by using one of the logging commands:

$ heroku logs
Fetching logs...

To generate more log messages, refresh the app’s homepage in your browser.

$ heroku logs
Fetching logs...

2024-11-28T16:24:13.159446+00:00 app[web-756cc855b6-zhdlv]: 2024-11-28 16:24:13 [34mINFO [0;39m [36mplay.api.Play[0;39m [35m[0;39m Application started (Prod) (no global state)
2024-11-28T16:24:14.362817+00:00 app[web-756cc855b6-zhdlv]: 2024-11-28 16:24:14 [34mINFO [0;39m [36mplay.core.server.AkkaHttpServer[0;39m [35m[0;39m Listening for HTTP on /[0:0:0:0:0:0:0:0]:8000

To stop streaming the logs, press Control+C.

Declare App Dependencies

Heroku recognizes an app as a Scala app by the existence of a build.sbt file in the root directory.

The demo app you deployed already has a build.sbt:

name := """scala-getting-started"""
organization := "com.heroku"

version := "1.0-SNAPSHOT"

lazy val root = (project in file(".")).enablePlugins(PlayScala)

scalaVersion := "2.13.10"

libraryDependencies += guice
libraryDependencies += jdbc
...

The build.sbt file specifies the dependencies to install with your application.

Run sbt stage in your local directory to install the dependencies, preparing your system for running the app locally:

$ sbt stage
[info] welcome to sbt 1.7.2 (Homebrew Java 17.0.12)
[info] loading global plugins from /Users/manuel.fuchs/.sbt/1.0/plugins
[info] loading settings for project scala-getting-started-build from plugins.sbt ...
[info] loading project definition from /private/var/folders/fc/dw_bf9wd5sb512b0cwn3wp2w0000gp/T/d20241128-11221-talylm/scala-getting-started/project
[info] loading settings for project root from build.sbt ...

Push Local Changes

In this step, you propagate a local change to the application to Heroku.

Modify build.sbt to include an additional dependency for the jscience to libraryDependencies.

In file build.sbt, on line 16 add:

    "org.jscience" % "jscience" % "4.3.1",

Add the import statements for the library.

In file app/controllers/Application.scala, on line 2 add:

import org.jscience.physics.amount.Amount
import org.jscience.physics.model.RelativisticModel
import javax.measure.unit.SI

Add a new convert method.

In file app/controllers/Application.scala, on line 14 add:

def convert(): Action[AnyContent] = Action { implicit request: Request[AnyContent] =>
    RelativisticModel.select()
    val energy = Amount.valueOf("12 GeV");

    Ok("E=mc^2: " + energy + " = " + energy.to(SI.KILOGRAM))
}

Add a new route to the new action.

In file conf/routes, on line 7 add:

GET     /convert                    controllers.Application.convert()

Now test locally:

$ sbt stage
$ heroku local --port=5006

Visit your application’s /convert path at http://localhost:5006/convert. If your changes worked, you see scientific conversions:

E=mc^2: 12 GeV = (2.139194076302506E-26 ± 1.4E-42) kg

Now deploy this local change to Heroku.

Almost every deploy to Heroku follows this same pattern. First, add the modified files to the local Git repository:

$ git add .

Now commit the changes to the repository:

$ git commit -m "Add convert endpoint"
[main 81d47b1] Add convert endpoint
 4 files changed, 37 insertions(+)
 create mode 100644 install.txt

Now deploy as before:

$ git push heroku main

Finally, check that everything is working:

$ heroku open

Debugging

The Heroku Scala Cloud Native Buildpack turns your code into an Open Container Initiative (OCI) container image when you deploy to Fir. This image gets executed on our dynos.

You can use this image locally to reproduce and debug deployment problems. Build an OCI image from your application to debug locally by using the Heroku Scala Cloud Native Buildpack. If you’re interested, check out the buildpack docs.

Start a One-off Dyno

The heroku run command to launch an interactive one-off dyno is unavailable for Fir. As an alternative, use heroku run:inside to access a running dyno until we add heroku run for Fir.

To execute the command you need the name of a currently running process. You can see a list with heroku ps:

$ heroku ps
=== web (1X-Classic): target/universal/stage/bin/scala-getting-started -Dhttp.port=${PORT} (1)

web-756cc855b6-zhdlv: up 2024/11/28 17:24:15 +0100 (~ 39s ago)

Use that dyno name to run a command like java -version by prepending launcher to it:

$ heroku run:inside web-756cc855b6-zhdlv "launcher java -version"
Running launcher java -version on ⬢ morning-hollows-66944... up, web-756cc855b6-zhdlv
Picked up JAVA_TOOL_OPTIONS: -Xmx300m -Xss512k -XX:CICompilerCount=2 -Dfile.encoding=UTF-8
openjdk version "17.0.12" 2024-07-16 LTS
OpenJDK Runtime Environment Zulu17.52+17-CA (build 17.0.12+7-LTS)
OpenJDK 64-Bit Server VM Zulu17.52+17-CA (build 17.0.12+7-LTS, mixed mode, sharing)

If you receive an error, Error connecting to process, configure your firewall.

Let’s try another example. Create another one-off process within your running dyno and run the bash command to open up a shell on that dyno. You can then execute commands there.

$ heroku run:inside web-756cc855b6-zhdlv "launcher bash"
Running launcher bash on ⬢ morning-hollows-66944... up, web-756cc855b6-zhdlv
heroku@web-756cc855b6-zhdlv:/workspace$

You can use this to view the contents of the dyno’s disk:

~ $ ls
LICENSE         app.json        project
Procfile        build.sbt       public
Procfile.windows    build.sc        system.properties
README.md       conf            target
app         install.txt
~ $ exit
exit

Type exit to exit the shell and terminate the dyno.

Define Config Vars

Heroku lets you externalize configuration by storing data such as encryption keys or external resource addresses in config vars.

At runtime, we expose config vars as environment variables to the application.

For example, modify Application.scala so that the method obtains an energy value from the ENERGY environment variable:

def convert(): Action[AnyContent] = Action { implicit request: Request[AnyContent] =>
    RelativisticModel.select()

    Ok(sys.env.get("ENERGY")
            .map(Amount.valueOf)
            .map(energy => "E=mc^2: " + energy + " = " + energy.to(SI.KILOGRAM))
            .getOrElse("ENERGY environment variable is not set!"))
}

The heroku local command automatically sets up the environment based on the contents of the .env file in your local directory. In the top level directory of your sample project, there’s already a .env file that contains:

ENERGY=20 GeV

If you run the app with heroku local --port=5006 and visit http://localhost:5006/convert to see the conversion value for 20 GeV.

To set the config var on Heroku, execute the following:

$ heroku config:set ENERGY="20 GeV"
Setting ENERGY and restarting morning-hollows-66944...
Setting ENERGY and restarting morning-hollows-66944... done, v5
ENERGY: 20 GeV

View the app’s config vars using heroku config:

$ heroku config
ENERGY: 20 GeV
...

To see this change in action, deploy your changed application to Heroku.

Use a Database

Listing the config vars for your app displays the URL that your app uses to connect to the database, DATABASE_URL:

$ heroku config
DATABASE_URL:                postgres://xx:yyy@host:5432/d8slm9t7b5mjnd
HEROKU_POSTGRESQL_BROWN_URL: postgres://xx:yyy@host:5432/d8slm9t7b5mjnd
...

Heroku also provides a pg command that shows a lot more information:

$ heroku pg
=== DATABASE_URL

Plan:                  essential-0
Status:                Available
Connections:           unknown/20
PG Version:            16.3
Created:               2024-11-28 16:18
Data Size:             unknown usage / 1 GB (In compliance)
Tables:                0/4000 (In compliance)
Fork/Follow:           Unsupported
Rollback:              Unsupported
Continuous Protection: Off
Add-on:                postgresql-animated-10652

The example app you deployed already has database functionality. You can visit the page by appending /database to your app’s URL.

Database Output

* Read from DB: 2024-11-27 13:07:53.002632
* Read from DB: 2024-11-27 13:07:54.965283
* Read from DB: 2024-11-27 13:07:55.620596

If you have Postgres installed locally, you can also interact directly with the database. For example, here’s how to connect to the database using psql and execute a query:

$ heroku pg:psql -c "SELECT * FROM ticks"
--> Connecting to postgresql-animated-10652
            tick
----------------------------
 2024-11-28 16:27:48.032932
 2024-11-28 16:27:49.761292
 2024-11-28 16:27:53.055597
(3 rows)

Read more about Heroku PostgreSQL.

Delete Your App and Add-on

Remove the app and database from your account. We only charge you for the resources you used.

$ heroku addons:destroy heroku-postgresql

$ heroku apps:destroy

You can confirm that your add-on and app are gone with these commands:

$ heroku addons --all
$ heroku apps --all

Next Steps

You’re now ready to deploy your app. You now know how to deploy an app, change its configuration, view logs, scale, and attach add-ons.

Here’s some recommended reading:

• Read How Heroku Works for a technical overview of the concepts you encounter while writing, configuring, deploying, and running applications.
• To learn more about developing and deploying Scala applications, visit the Scala support category.