Getting Started with Gradle on Heroku

Introduction

This tutorial will have you deploying a Gradle app in minutes.

Hang on for a few more minutes to learn how it all works, so you can make the most out of Heroku.

The tutorial assumes that you have:

a free Heroku account
Java 8 installed

If you’d prefer to use Maven instead of Gradle, please see the Getting Started on Heroku with Java guide.

Set up

In this step you will install the Heroku Command Line Interface (CLI), formerly known at the Heroku Toolbelt. You will use the CLI to manage and scale your applications, to provision add-ons, to view the logs of your application as it runs on Heroku, as well as to help run your application locally.

Download the Heroku CLI

Once installed, you can use the heroku command from your command shell.

On Windows, start the Command Prompt (cmd.exe) or Powershell to access the command shell.

$ heroku login
Enter your Heroku credentials.
Email: java@example.com
Password:

Authenticating is required to allow both the heroku and git commands to operate.

Note that if you’re behind a firewall that requires use of a proxy to connect with external HTTP/HTTPS services, you can set the HTTP_PROXY or HTTPS_PROXY environment variables in your local development environment before running the heroku command.

Prepare the app

In this step, you will prepare a simple application that can be deployed.

Execute the following commands to clone the sample application:

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

You now have a functioning Git repository that contains a simple application as well as a build.gradle file, which is used by the Gradle dependency manager.

Deploy the app

In this step you will deploy the app to Heroku.

Create an app on Heroku, which prepares Heroku to receive your source code:

$ heroku create
Creating warm-eyrie-9006... done, stack is cedar-14
http://warm-eyrie-9006.herokuapp.com/ | https://git.heroku.com/warm-eyrie-9006.git
Git remote heroku added

When you create an app, a Git remote (called heroku) is also created and associated with your local Git repository.

Heroku generates a random name (in this case warm-eyrie-9006) for your app, or you can pass a parameter to specify your own app name.

Now deploy your code:

$ git push heroku master
Counting objects: 50, done.
Delta compression using up to 4 threads.
Compressing objects: 100% (36/36), done.
Writing objects: 100% (50/50), 55.64 KiB | 0 bytes/s, done.
Total 50 (delta 8), reused 0 (delta 0)
remote: Compressing source files... done.
remote: Building source:
remote:
remote: -----> Gradle app detected
remote: -----> Installing OpenJDK 1.8... done
remote: -----> Building Gradle app...
remote:        WARNING: The Gradle buildpack is currently in Beta.
remote: -----> executing ./gradlew stage
remote:        Downloading https://services.gradle.org/distributions/gradle-2.3-bin.zip

...
-----> Discovering process types
       Procfile declares types -> web

-----> Compressing... done, 62.7MB
-----> Launching... done, v7
       http://warm-eyrie-9006.herokuapp.com/ deployed to Heroku

To git@heroku.com:warm-eyrie-9006.git
 * [new branch]      master -> master

The application is now deployed. Ensure that at least one instance of the app is running:

$ heroku ps:scale web=1

Now visit the app at the URL generated by its app name. As a handy shortcut, you can 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, providing a single channel for all of the events.

View information about your running app using one of the logging commands, heroku logs:

$ heroku logs --tail
2015-07-30T01:01:35.036041+00:00 heroku[web.1]: Starting process with command `build/install/gradle-getting-started/bin/gradle-getting-started`
2015-07-30T01:01:37.376666+00:00 app[web.1]: Picked up JAVA_TOOL_OPTIONS: -Xmx384m -Xss512k -Dfile.encoding=UTF-8
2015-07-30T01:01:44.383944+00:00 app[web.1]: [main] WARN io.netty.channel.DefaultChannelId - Failed to find a usable hardware address from the network interfaces; using random bytes: e3:85:b3:ca:fd:ff:84:43
2015-07-30T01:01:44.423925+00:00 app[web.1]: [main] INFO ratpack.server.RatpackServer - Ratpack started for http://localhost:14791
2015-07-30T01:01:44.644074+00:00 heroku[web.1]: State changed from starting to up

Visit your application in the browser again, and you’ll see another log message generated. Press Control+C to stop streaming the logs.

Define a Procfile

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

The Procfile in the example app you deployed looks like this:

web: build/install/gradle-getting-started/bin/gradle-getting-started

This 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 will be attached to the HTTP routing stack of Heroku, and receive web traffic when deployed.

The syntax of the Procfile is important. Heroku runs the exact command specified here when it starts a web dyno and it runs it in a Unix environment.

When running locally under Windows, you may receive an error because the Unix way of passing in environment variables ($JAVA_OPTS) and of concatenating paths (:) is incompatible.

Procfiles can contain additional process types. For example, you might declare one for a background worker process that processes items off of a queue.

Scale the app

Right now, your app is running on a single web dyno. Think of a dyno as a lightweight container that runs the command specified in the Procfile.

You can check how many dynos are running using the ps command:

$ heroku ps
=== web (Free): `build/install/gradle-getting-started/bin/gradle-getting-started`
web.1: up 2014/08/08 14:55:07 (~ 2m ago)

By default, your app is deployed on a free dyno. Free dynos will sleep after a half hour of inactivity (if they don’t receive any traffic). This causes a delay of a few seconds for the first request upon waking. Subsequent requests will perform normally. Free dynos also consume from a monthly, account-level quota of free dyno hours - as long as the quota is not exhausted, all free apps can continue to run.

To avoid dyno sleeping, you can upgrade to a hobby or professional dyno type as described in the Dyno Types article. For example, if you migrate your app to a professional dyno, you can easily scale it by running a command telling Heroku to execute a specific number of dynos, each running your web process type.

For abuse prevention, scaling the application requires account verification. If your account has not been verified, you will be directed to visit the verification site.

Declare app dependencies

Heroku recognizes an app as a Gradle app by the existence of a gradlew or build.gradle file in the root directory.

The demo app you deployed already has a build.gradle (see it here). Here’s an excerpt:

dependencies {
  runtime "org.slf4j:slf4j-simple:1.7.12"
  ...
}

task stage {
  dependsOn installDist
}

The build.gradle file specifies dependencies that should be installed with your application. When an app is deployed, Heroku reads this file and installs the dependencies using the ./gradlew stage command.

Another file, system.properties, determines the version of Java to use. (Heroku supports many different versions). The contents of this file, which is optional, are quite straightforward:

java.runtime.version=1.8

Run the Gradle stage task in your local directory to install the dependencies, preparing your system for running the app locally. Note that this app requires Java 8, but that you can push your own apps using a different version of Java.

On Windows, run this comannd

> gradlew.bat stage

On Mac and Linux run this command:

$ ./gradlew stage

In either case, you’ll see output like this:

:compileJava UP-TO-DATE
:compileGroovy UP-TO-DATE
:prepareBaseDir UP-TO-DATE
:processResources
:classes
:jar
:startScripts
:installDist
:stage

BUILD SUCCESSFUL

Total time: 7.666 secs

If you see an error such as Unsupported major.minor version 52.0, then Gradle is trying to use Java 7. Check that your JAVA_HOME environment variable is set correctly.

The Gradle process will copy the dependencies into your application’s build/install/gradle-getting-started/lib directory. This process is called “vendoring”, and it is done by default in a Ratpack app, such as the sample. But it can also be done manually as described in the Deploying Gradle Apps on Heroku guide.

Once dependencies are installed, you will be ready to run your app locally.

Run the app locally

To run the app locally, first ensure that you’ve run the gradlew stage task as described in the previous section. Then start your application using the heroku local command, which was installed as part of the Heroku CLI.

On Windows, be sure to add the -f Procfile.windows option to this command because the default Procfile is specific to Linux.

$ heroku local web
20:14:17 web.1  | started with pid 30989
20:14:19 web.1  | [main] INFO ratpack.server.RatpackServer - Ratpack started for http://localhost:5000

Just like Heroku, heroku local examines the Procfile to determine what to run. It also defines the port your app will bind to by setting the PORT environment variable. Ratpack detects this by default, but you may need to detect it manually if you are using another framework.

Your app will now be running at http://localhost:5000. Test that it’s working with curl or a web browser, then Ctrl+C to exit.

heroku local doesn’t just run your app - it also sets “config vars”, something you’ll encounter in a later tutorial.

Push local changes

In this step you’ll learn how to propagate a local change to the application through to Heroku. As an example, you’ll modify the application to add an additional dependency and the code to use it.

Modify build.gradle to include a dependency for jscience. The dependencies section should look something like this:

dependencies {
  runtime "org.slf4j:slf4j-simple:1.7.12"
  compile "com.heroku.sdk:heroku-jdbc:0.1.1"
  compile "org.postgresql:postgresql:9.4-1201-jdbc4"
  compile "org.jscience:jscience:4.3.1"
}

Modify src/main/java/Main.java so that it imports this library at the start, by including the following imports:

import static javax.measure.unit.SI.KILOGRAM;
import javax.measure.quantity.Mass;
import org.jscience.physics.model.RelativisticModel;
import org.jscience.physics.amount.Amount;

And modify the get("hello",...) handler so that it reads like this:

.get("hello", ctx -> {
  RelativisticModel.select();
  Amount<Mass> m = Amount.valueOf("12 GeV").to(KILOGRAM);
  ctx.render("E=mc^2: 12 GeV = " + m.toString());
})

Here’s the final source code for Main.java - yours should look similar. Here’s a diff of all the local changes you should have made.

Now test locally:

$ ./gradlew stage
$ heroku local web

Visiting your application on the /hello route at http://localhost:5000/hello, you should see some great scientific conversions displayed:

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

Now deploy. 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 "Demo"

Now deploy, just as you did previously:

$ git push heroku master

Finally, check that everything is working:

$ heroku open

Provision add-ons

Add-ons are third-party cloud services that provide out-of-the-box additional services for your application, from persistence through logging to monitoring and more.

By default, Heroku stores 1500 lines of logs from your application. However, it makes the full log stream available as a service - and several add-on providers have written logging services that provide things such as log persistence, search, and email and SMS alerts.

In this step you will provision one of these logging add-ons, Papertrail.

Provision the Papertrail logging add-on:

$ heroku addons:create papertrail
Adding papertrail on warm-eyrie-9006... done, v8 (free)
Welcome to Papertrail. Questions and ideas are welcome (support@papertrailapp.com). Happy logging!
Use `heroku addons:docs papertrail` to view documentation.

To help with abuse prevention, provisioning an add-on requires account verification. If your account has not been verified, you will be directed to visit the verification site.

The add-on is now deployed and configured for your application. You can list add-ons for your app like this:

$ heroku addons

To see this particular add-on in action, visit your application’s Heroku URL a few times. Each visit will generate more log messages, which should now get routed to the Papertrail add-on. Visit the Papertrail console to see the log messages:

$ heroku addons:open papertrail

Your browser will open up a Papertrail web console, showing the latest log events. The interface lets you search and set up alerts:

Start a one-off dyno

You can run a command, typically scripts and applications that are part of your app, in a one-off dyno using the heroku run command. It can also be used to launch a REPL process attached to your local terminal for experimenting in your app’s environment, or code that you deployed with your application:

$ heroku run bash
Running `bash` attached to terminal... up, run.9640
~ $ java -version
openjdk version "1.8.0_51-cedar14"
OpenJDK Runtime Environment (build 1.8.0_51-cedar14-b16)
OpenJDK 64-Bit Server VM (build 25.51-b03, mixed mode)

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

Don’t forget to type exit to exit the shell and terminate the dyno.

Define config vars

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

At runtime, config vars are exposed as environment variables to the application. For example, modify src/main/java/Main.java so that the method repeats grabs an energy value from the ENERGY environment variable:

.get("hello", ctx -> {
  RelativisticModel.select();

  String energy = System.getenv("ENERGY");

  Amount<Mass> m = Amount.valueOf(energy).to(KILOGRAM);
  ctx.render("E=mc^2: " + energy + " = " + m.toString());
})

Now compile the app again so that this change is integrated by running ./gradlew stage or gradlew.bat stage respectively.

The heroku local command will automatically set up the environment based on the contents of the .env file in your local directory. In the top-level directory of your project there is already a .env file that has the following contents:

ENERGY=20 GeV

If you run the app with heroku local web and visit it at http://localhost:5000, you’ll see the conversion value for 20 GeV.

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

$ heroku config:set ENERGY="20 GeV"
Setting config vars and restarting warm-eyrie-9006... done, v10
ENERGY: 20 GeV

View the config vars that are set using heroku config:

$ heroku config
== warm-eyrie-9006 Config Vars
PAPERTRAIL_API_TOKEN: erdKhPeeeehIcdfY7ne
ENERGY: 20 GeV
...

Deploy your changed application to Heroku to see this in action.

Use a database

The add-on marketplace has a large number of data stores, from Redis and MongoDB providers, to Postgres and MySQL. In this step you will learn about the free Heroku Postgres add-on.

To begin, attach a new instance of the PostgreSQL add-on to your app by running this command:

$ heroku addons:create heroku-postgresql
Creating postgresql-transparent-1523... done, (free)
Adding postgresql-transparent-1523 to warm-eyrie-9006... done
Setting DATABASE_URL and restarting warm-eyrie-9006... done, v3
Database has been created and is available
 ! This database is empty. If upgrading, you can transfer
 ! data from another database with pgbackups:restore
Use `heroku addons:docs heroku-postgresql` to view documentation.

You can find out a little more about the database provisioned for your app using the addons command in the CLI:

$ heroku addons
=== Resources for warm-eyrie-9006
Plan                         Name                Price
---------------------------  ------------------  -----
heroku-postgresql:hobby-dev  singing-aptly-6889  free
papertrail:choklad           gazing-nimbly-9108  free

=== Attachments for warm-eyrie-9006
Name        Add-on              Billing App
----------  ------------------  -----------------
DATABASE    singing-aptly-6889  warm-eyrie-9006
PAPERTRAIL  gazing-nimbly-9108  warm-eyrie-9006

Listing the config vars for your app will display the URL that your app is using to connect to the database, DATABASE_URL:

$ heroku config
=== warm-eyrie-9006 Config Vars
DATABASE_URL:               postgres://qplhasewkhqyxp:YXDPSRus9MrU4HglCPzjhOevee@ec2-54-204-47-58.compute-1.amazonaws.com:5432/dc9qsdnghia6v1
...

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

$ heroku pg
== HEROKU_POSTGRESQL_BLUE_URL (DATABASE_URL)
Plan:        Hobby-dev
Status:      Available
Connections: 0
PG Version:  9.3.3
Created:     2014-08-08 13:54 UTC
Data Size:   6.5 MB
Tables:      0
Rows:        0/10000 (In compliance)
Fork/Follow: Unsupported
Rollback:    Unsupported

This indicates I have a hobby database (free), running Postgres 9.3.3, with a single row of data.

The example app you deployed already has database functionality, which you should be able to reach by visiting your app’s URL and appending /db. For example, if your app was deployed to https://wonderful-app-287.herokuapp.com/ then visit https://wonderful-app-287.herokuapp.com/db.

The code to access the database is straightforward. Here’s the method to insert values into a table called tick:

.get("db", ctx -> {
  Connection connection = null;
  Map<String, Object> attributes = new HashMap<>();
  try {
    connection = DatabaseUrl.extract(true).getConnection();

    Statement stmt = connection.createStatement();
    stmt.executeUpdate("CREATE TABLE IF NOT EXISTS ticks (tick timestamp)");
    stmt.executeUpdate("INSERT INTO ticks VALUES (now())");
    ResultSet rs = stmt.executeQuery("SELECT tick FROM ticks");

    ArrayList<String> output = new ArrayList<String>();
    while (rs.next()) {
      output.add( "Read from DB: " + rs.getTimestamp("tick"));
    }

    attributes.put("results", output);
    ctx.render(groovyTemplate(attributes, "db.html"));
  } catch (Exception e) {
    attributes.put("message", "There was an error: " + e);
    ctx.render(groovyTemplate(attributes, "error.html"));
  } finally {
    if (connection != null) try{connection.close();} catch(SQLException e){}
  }
})

This ensures that when you access your app using the /db route, a new row will be added to the tick table, and all the rows will then be returned so that they can be rendered in the output.

The DatabaseUrl.extract() method, which is made available via the heroku-jdbc dependency in the build.gradle, retrieves the DATABASE_URL environment variable, set by the database add-on, and establishes a connection.

Deploy your change to Heroku by committing the changes to Git, and then running git push heroku master.

Now, when you access your app’s /db route, you will see something like this:

Database Output
* Read from DB: 2014-08-08 14:48:25.155241
* Read from DB: 2014-08-08 14:51:32.287816
* Read from DB: 2014-08-08 14:51:52.667683

Assuming that you have Postgres installed locally, use the heroku pg:psql command to connect to the remote database and see all the rows:

$ heroku pg:psql
heroku pg:psql
psql (9.3.2, server 9.3.3)
SSL connection (cipher: DHE-RSA-AES256-SHA, bits: 256)
Type "help" for help.
=> SELECT * FROM ticks;
            tick
----------------------------
 2014-08-08 14:48:25.155241
 2014-08-08 14:51:32.287816
 2014-08-08 14:51:52.667683
 2014-08-08 14:51:53.1871
 2014-08-08 14:51:54.75061
 2014-08-08 14:51:55.161848
 2014-08-08 14:51:56.197663
 2014-08-08 14:51:56.851729
(8 rows)
=> \q

Next steps

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

Here’s some recommended reading. The first, an article, will give you a more firm understanding of the basics. The last is a pointer to the main Java category here on Dev Center:

Read How Heroku Works for a technical overview of the concepts you’ll encounter while writing, configuring, deploying and running applications.
Read Deploying Gradle Apps on Heroku to understand how to take an existing Java app and deploy it to Heroku.
Visit the Java category to learn more about developing and deploying Java applications.