Getting Started with Clojure on Heroku

Last week I introduced the Den of Clojure to Heroku. I really enjoyed learning more about Clojure and experiencing super simple Clojure deployment on Heroku. For those who haven’t yet deployed Clojure on Heroku, lets walk through 8 quick steps to get you started:

  1. Install the Heroku Toolbelt and Leiningen
  2. Login to Heroku from the command line:
    heroku login

    If this is your first time logging into Heroku from the command line then you will be led through some steps to associate an SSH key with your Heroku account.

  3. Create a new Leiningen build definition by creating a file named project.clj containing:
    (defproject hello-clojure-noir "0.1.0-SNAPSHOT"
      :main web
      :dependencies [[org.clojure/clojure "1.4.0"]
                     [noir "1.2.1"]])

    As you can see from the dependencies, this simple app uses the Noir web framework.

  4. Create a simple Noir app by creating a file named src/web.clj containing:
    (ns web
      (:use noir.core)
      (:require [noir.server :as server]))
     
    (defpage "/" [] "hello, world")
     
    (server/start (Integer/parseInt (or (System/getenv "PORT") "8080")))

    This very basic web app returns “hello, world” for requests to “/”. It starts the server using either the port defined by an environment variable named “PORT” or a default of 8080.

  5. Test this app locally by running:
    lein run

    Then visit http://localhost:8080 in your browser and verify that you see “hello, world”.

  6. To upload this application to Heroku you will first need to create a Git repository, add the files to it, and commit them:
    git init
    git add project.clj src
    git commit -m init
  7. Now create a new application on Heroku:
    heroku create

    This creates an HTTP and a Git endpoint for your application. The Git endpoint will be added to your Git configuration as a “remote” named “heroku”.

  8. Upload your Git repository to the Git repository for your application on Heroku:
    git push heroku master

    This will kick off the Leiningen build process on Heroku. The build will download the dependencies for the app then compile the app and put everything into a “slug” that will be deployed onto a Dyno. Once the process is complete you can open the HTTP endpoint for your app in your browser:

    heroku open

    You should now see “hello, world” coming from the Cloud!

The source for this example is on GitHub.

To learn more about Clojure on Heroku, check out the Heroku Dev Center. Let me know how it goes!

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  • Phil Hagelberg

    Thanks for posting this, James. I thought I’d add a note about my Heroku lein-template project: https://github.com/technomancy/lein-heroku/tree/master/lein-template

    If you’re on Leiningen 2.x (and if you’re not, you should try it), you can run `lein new heroku myapp` to have a ready-made skeleton project written with Compojure, a Procfile, etc. I should have a new version out soon that adds support for easier environment config and embeds an HTTP repl server.



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