Configuration

In this chapter, we'll learn how to manage different configurations for our applications (locally and in production).

Environment variables

The best way to configure an application on Heroku is to use environment variables. It's a key value storage managed by the system that can affect the way running processes will behave on a computer.

Exemple of an env variable:

MESSAGE=Hello World

You can list all current environment variables using the command env.

Heroku defines by default 2 environement variables:

• PORT which equals the port our application should be running on.

• DYNO which gives you a id/name for the current process dyno.

With Node.js

In Node.js, it's really easy to read environment variable, the varibale process.env is an object containing all current env variables.

We already used it to start our application on the right port: var port = Number(process.env.PORT || 5000);.

Notice that environment variables are always string.

Modifying our application

We are going to change our application to show a message instead of "Hello World" that will be stored in a en environment variables.

Edit the main.js file to change the app.get to:

app.get('/', function(req, res) {
  res.send(process.env.MESSAGE || 'Default message!');
});

If you run the application using foreman start and access http://localhost:5000, you'll see : Default message!.

But you can test changing the value of MESSAGE in your terminal and running the application with:

$ export MESSAGE=Hello
$ foreman start

Storing a fixed configuration for foreman

You don't want to define using export our all configuration each time you want to start working on your application!

So we need to store our configuration in a file. By default foreman use a file named .env but we are going to use this file for your production configuration.

So we'll store our configuration in a file named .env.local:

MESSAGE=Hello from the local version

And we need to update foreman configuration by writting the file .foreman:

port: 5000
env: .env.local

You can then test using foreman start and see teh output: Hello from the local version.

Deployment of a production configuration

We are going to store our production configuration in a file named .env:

MESSAGE=Hello from the production version

Then we need to commit all these changes and deploy the last update of our code to Heroku:

# Commit changes
$ git add .
$ git commit -m "Use environment variables as configuration"

# Deploy to heroku
$ git push heroku master

But if you take a look at your application (using heroku open), you can see that the message is still "Default message!". It's because we didn't pushed your configuration to heroku yet.

For this we are going to use the plugin heroku-config, install it using:

$ heroku plugins:install git://github.com/ddollar/heroku-config.git

And then we can push our all configuration using:

$ heroku config:push

Now take a look at your application and you'll see "Hello from the production version".

Managing Heroku configuration by hand

I want to...	Command
List all my configuraton	heroku config
Get a variable value	heroku config:get MESSAGE
Set a variable value	heroku config:set MESSAGE=Test
Delete a variable	heroku config:unset MESSAGE

And with the plugin heroku-config:

I want to...	Command
Push my .env to heroku	heroku config:push
Update my .env with my heroku config	heroku config:pull
Rewrite my .env with my heroku config	heroku config:pull --overwrite