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Deploying Clojure Applications with the Heroku Leiningen Plugin

Last updated 24 April 2019

In addition to Git deployment, Heroku supports building and releasing apps via an API. The lein-heroku plugin uses this API to provide direct deployment of prepackaged standalone web applications to Heroku.

This may be a preferred approach for applications that take a long time to compile or need to be deployed from a continuous integration server such as Travis CI or Jenkins.

In this article, you’ll learn how to include the Heroku Leiningen Plugin in your project, configure it, and deploy your application to Heroku.

Adding the plugin

To include the plugin in your project, add the following to your project.clj file’s :plugins vector:

Install the Heroku CLI and run the create command.

$ heroku create
Creating obscure-sierra-7788... done, stack is heroku-18
http://obscure-sierra-7788.herokuapp.com/ | git@heroku.com:obscure-sierra-7788.git

If you do not have a Heroku Git repo in your git remotes, add something like this to your project.clj .

:heroku {:app-name "your-heroku-app-name"}

Make sure your project has a Procfile, and you’re ready to deploy.

Deploying an app

Run the following command from the root directory of your project to deploy the app to Heroku:

$ lein heroku deploy
-----> Packaging application...
       - app: obscure-sierra-7788
       - including: target/clojure-getting-started-standalone.jar
-----> Creating build...
       - file: target/heroku/slug.tgz
       - size: 5MB
-----> Uploading build...
       - success
-----> Deploying...
remote:
remote: -----> Fetching custom tar buildpack... done
remote: -----> JVM Common app detected
remote: -----> Installing OpenJDK 1.8... done
remote: -----> Discovering process types
remote:        Procfile declares types -> web
remote:
remote: -----> Compressing... done, 53.9MB
remote: -----> Launching... done, v6
remote:        https://obscure-sierra-7788.herokuapp.com/ deployed to Heroku
remote:
-----> Done

Visit your application with this command:

$ heroku open -a obscure-sierra-7788

Or view the logs with this command:

$ heroku logs -a obscure-sierra-7788

The Heroku CLI will allow you to access the application, and run commands just like an application deployed with git push.

Configuring the plugin

You may set a :heroku element in your project.clj like this:

:heroku {
  :app-name "your-heroku-app-name"
  :jdk-version "1.8"
  :include-files ["target/myapp.jar"]
  :process-types { "web" "java -jar target/myapp.jar" }}

By default, the plugin will include the target directory in your slug file.

Requirements

• Your application must be built as an uberjar.
• You must use Java 1.7 or higher locally.

For more information on the plugin and Clojure in general, see Heroku’s Clojure support. For more information on Leiningen, see the Leiningen documentation.