Sample Clojure webapp running on clever-cloud

Why?

There is no official clojure & leiningen support at the moment on clever-cloud, even if I’m sure that this is totally on track? 😃.

But it’s really easy to achieve it by building locally (or Jenkins or whatever) and using the JAR deployement support of clever-cloud.

Prerequisites

You will need Java and Leiningen installed on your machine, but if you are already a fan of Clojure, you got this covered.

GitHub

You can find the sources of the whole application & tutorial at the following URL: https://github.com/agrison/hello-clj-clever-cloud

Create the application

Bootstrap

lein compojure new app

Edit the app

Then just for fun, bump some versions, in order to use bleeding edge state-of-the-art fully unicorn-approved awesome technology.

Edit project.clj:

(defproject app "0.1.0-SNAPSHOT"
  :description "FIXME: write description"
  :url "http://example.com/FIXME"
  :min-lein-version "2.0.0"
  :dependencies [[org.clojure/clojure "1.9.0-alpha5"]
                 [compojure "1.5.1"]      
                 [ring/ring-defaults "0.2.1"]
                 [ring/ring-jetty-adapter "1.5.0"]   
                 [ring "1.5.0"]]                     
  :plugins [[lein-ring "0.9.7"]]
  :ring {:handler app.handler/app}
  :profiles
  {:dev {:dependencies [[javax.servlet/servlet-api "2.5"]
                        [ring/ring-mock "0.3.0"]]}}
  :main app.handler)

We will need a standalone JAR, in order to do that, our handler namespace needs to generate a Java class using (:gen-class) and we need a main method that starts jetty on port 8080 (default port for a clever-cloud application).

Edit src/app/handler.clj:

(ns app.handler
  (:gen-class)
  (:require [compojure.core :refer :all]
            [compojure.route :as route]
            [compojure.handler :as handler]
            [ring.adapter.jetty :as jetty]]))

(defroutes app-routes
  (GET "/" [] "Hello World")
  (route/not-found "Not Found"))

(def app
  (handler/site app-routes))

(defn -main [& args]
  (jetty/run-jetty app {:port 8080}))

clever-cloud specifics

As explained on the clever-cloud docs regarding JAR deployment, add a jar.json file to the clevercloud/ directory:

cat <<EOF > clevercloud/jar.json
{
    "deploy": {
    "jarName": "target/app-0.1.0-SNAPSHOT-standalone.jar"
  }
}
EOF

That way, clever-cloud knows what JAR to deploy & run.

That’s it

Yes, that’s all there is to it.

Build

lein uberjar
# add the jar to repository
git add -f target/app-0.1.0-SNAPSHOT-standalone.jar
git push -u origin master

clever-cloud

Go sign-in or create an account on clever-cloud then load your personal dashbord.

Add an application

Create an application from a Github repository

Select Java + Maven

Newly created java applications run on java 8 by default. You can set the java version with the JAVA_VERSION environment variable.

Edit the instance (if you want)

By default it will select an XS instance, for such a hello world application, I will select a pico instance.

Click the EDIT button:

Click the pico circle button, then NEXT:

Create the application

Click the CREATE button:

Select your addons

For this simple hello world app I click I DON’T NEED ANY ADD-ON:

Start the application

Click the play button under This app is currently stopped:

Then click the read logs link above that pretty little orange circle:

Wait for the build to success

Wait for the app to deploy

Check that the application is UP

If you can see that little comforting green circle:

Open the application

Click that Open the application button:

Profit!

You’re awesome.

Downside

• The uberjar can become large.
• You have to build locally and push that artifact.

Hopefully clever-cloud will support clojure and leiningen soon enough? 😃

Disclaimer

I’m not at all affiliated with clever-cloud even if I find @waxzce, @clementd and the rest of the clever-cloud team totally awesome for what they have built so far 😎