ibmcloud-cf-clojure

Clojure functional programming in Cloud Foundry

Get a simple Clojure web app running in Cloud Foundry on IBM Cloud.

After watching Russ Olsen at goto18 on YouTube, I thought I would go through the steps needed to start a Clojure app in the Cloud Foundry application runtime environment.

Russ mentioned the pedestal.io libraries as a way of bootstrapping a web runtime - this example is based on the pedestal hello-world sample.

Setup

IBM Cloud

Make sure you have an IBM Cloud account, and have installed the IBM Cloud command line tool.

Sample code

First, clone the pedestal repo:

git clone https://github.com/pedestal/pedestal.git

then navigate to the pedestal/samples/hello-world directory.

This folder contains a project.clj file, which is compatible with the heroku clojure buildpack -- although the Cloud Foundry docs point to mstine's buildpack repo, this hasn't been updated since 2013 -- the base heroku repo has moved on, so we'll use that instead.

Modify service configuration to also support Cloud Foundry

There are two files that make up the sample web app

• src/hello-world/service.clj - settings, routes and config for the app
• src/hello-world/server.clj - the application that listens for 'hello' requests

The default setting for http/port in service.clj is 8080 -- this is usually the port number passed to Cloud Foundry applications via the PORT environment variable, but it can vary; for completeness, we'll add support for that variability by replacing:

  ::http/port   8080

with:

  ::http/port   (read-string (or (System/getenv "PORT") "8080"))

(read-string is needed to convert the PORT value from string to number)

Also worth noting is that despite what all the Cloud Foundry doc samples suggest, trying to push an application which binds to a TCP port on localhost will not work - the server host needs to be unspecified, or set to "0.0.0.0". For that reason, the default bind address for the app needs to be set in the same way, with awareness of the VCAP_APP_HOST environment variable provided by Cloud Foundry:

  ::http/host   (or (System/getenv "VCAP_APP_HOST") "0.0.0.0")

Save these updates to src/hello-world/service.clj, and off we go.

Deploy to IBM Cloud Foundry

Pick a name for your application, then deploy to IBM Cloud using the "cf push" command.

We need to specify a couple of parameters:

• the name of the application
• the buildpack option, pointing to the Heroku/Cloud Foundry repository
• the memory size option - set to 256MB to ensure the app will run within the default limit for IBM Cloud Lite accounts (the default for the buildpack is 1GB!)

ibmcloud cf push <your-app-name> -m256m -b https://github.com/heroku/heroku-buildpack-clojure.git

Run the cf apps command to get the fully-qualified hostname for your application; from a browser connect to "https://< your-app-hostname >/hello?name=me", and you should see something like:

  Hello me!