Skeleton Application

The skeleton application is an app for you to get up and running as quickly as possible. Inside you’ll find the PHP libraries (vendor dir), a selection of useful modules, our recommended directory structure and some default configuration.

First, lets review the file structure of the PPI skeleton application:

www/                                        # your web root directory
└── skeleton/                               # the unpacked archive
    ├── app/
    │   ├── console                         # CLI script to help debug the application
    │   ├── init.php
    │   ├── config/                         # application configuration files
    │   │   ├── base/                       # base configuration to be extended by other environments
    │   │   │   ├── app.yml
    │   │   ├── dev/                        # configuration for the development environment (``dev``)
    │   │   │   └── app.yml
    │   │   ├── prod/                       # configuration for the production environment (``prod``)
    │   │   │   └── app.yml
    │   ├── cache/                          # application cache (must be writable by the web server)
    │   ├── logs/                           # application logs  (must be writable by the web server)
    │   └── views/                          # global template (view) files
    │       └── base.html.php
    ├── modules/                            # application modules
    │   ├── Application/
    │   ├── Framework/
    │   └── UserModule/
    ├── public/
    │   ├── index.php                       # front controller
    │   ├── css/
    │   ├── images/
    │   └── js/
    └── vendor/                             # libraries installed by Composer

Lets break it down into parts:

The public folder

The structure above shows you the /public/ folder. Anything outside of /public/ i.e: all your business code will be secure from direct URL access. In your development environment you don’t need a virtualhost file, you can directly access your application like so: http://localhost/skeleton/public/. In your production environment this will be All your publicly available asset files should be here, CSS, JS, Images.

The public index.php file

The /public/index.php is also known as your bootstrap file, or front controller and is presented below:


// All relative paths start from the main directory, not from /public/

// Setup autoloading and include PPI
require_once 'app/init.php';

// Set the environment
$env     = getenv('PPI_ENV') ?: 'dev';
$debug   = getenv('PPI_DEBUG') !== '0'  && $env !== 'prod';

// Create our PPI App instance
$app = new PPI\App(array(
    'environment'   => $env,
    'debug'         => $debug

// Configure the application

// Load the application, match the URL and send an HTTP response


PPI supports the notion of “environments” to make the application behave differently from when you are coding and testing the application in your laptop to when you deploy it to a production server. While in production debug messages won’t be logged, your application won’t stop due to non-fatal PHP errors and we’ll use caching wherever possible. In development you’ll get everything!

Auto-set the environment using web server variables

Editing index.php whenever you want to test the application in another environment can be tedious. An alternative is to set environment variables in your web server on a per vhost basis.

If you’re using Apache, environment variables can be set using the SetEnv directive.

Production VirtualHost configuration:

<VirtualHost *:80>
       ServerName    prod.skeletonapp.ppi.localhost
       DocumentRoot  "/var/www/skeleton/public"
       SetEnv        PPI_ENV prod
       SetEnv        PPI_DEBUG false

And a development VirtualHost configuration:

<VirtualHost *:80>
       ServerName    dev.skeletonapp.ppi.localhost
       DocumentRoot  "/var/www/skeleton/public"
       SetEnv        PPI_ENV dev
       SetEnv        PPI_DEBUG true

The front controller (index.php) needs to be slightly edited to load these environment variables:

// file: public/index.php

// Set the environment
$env     = getenv('PPI_ENV') ?: 'dev';
$debug   = getenv('PPI_DEBUG') !== '0'  && $env !== 'prod';

// Create our PPI App instance
$app = new PPI\App(array(
    'environment'   => $env,
    'debug'         => $debug

After this change http://prod.skeletonapp.ppi.localhost/ will use production settings while http://dev.skeletonapp.ppi.localhost/ is configured to work in development mode.

Creating a new environment

You don’t need to be restricted to the dev and prod environments. To create a new environment with a special configuration, let’s call it staging, just copy the folder contents of an existing environment to the new one and edit the app.yml file inside the staging dir.

$ cd /path/to/skeletonapp/app/config
$ cp -r prod staging
$ vim staging/app.yml

Now make sure public/index.php is picking up your new environment:

// ...

// Staging
$app = new PPI\App(array(
    'environment'   => 'staging',
    'debug'         => true


// ...


PPI creates cache and log files associated with each environment. For this new staging environment cache files will be available under app/cache/staging/ and the log file is available at app/logs/staging.log.

The app folder

This is where all your apps global items go such as app config, datasource config and modules config and global templates (views). You wont need to touch these out-of-the-box but it allows for greater flexibility in the future if you need it.

The app/config folder

Starting with version 2.1 all the application configuration lives inside app/config/<env>/ folders. Each <env> folder holds configuration for a specific environment: dev, prod.

Supported configuration formats

PPI supports both PHP and YAML formats. PHP is more powerful whereas YAML is more clean and readable. It is up to you to pick the format of your liking.


In 2.1 we changed the default configuration file format from PHP to YAML because (we think) it is less verbose and faster to type but don’t worry because PHP configuration files are and will always be supported.

YAML imports/include

The YAML language doesn’t natively provide the capability to include other YAML files like a PHP include or require statement. To overcome this limitation PPI supports two special syntaxes: imports and @include.


One of the goals of the PPI Framework is to provide an environment familiar to users coming from or going to the Symfony and Zend frameworks (among others). We support these two variants so these users do not need to worry about learning new syntaxes.


Available in the Symfony framework. Works like a PHP include statement providing base configuration to be tweaked in the current file. It is usually added at the top of the file.

    - { resource: ../base/app.yml }


Available in the Zend framework. Similar to the imports syntax but can be used also in a subelement of a value.

    @include: ../base/datasource.yml

The app.yml file

Looking at the example config file below, you can control things here such as the enabled templating engines, the datasource connection and the logger (monolog).

  • YAML
        - { resource: datasource.yml }
        - { resource: modules.yml }
            engines: ["php", "smarty", "twig"]
            path: "./utils/skeleton_module"
                type:  stream
                path:  %app.logs_dir%/%app.environment%.log
                level: debug
  • PHP
    $config = array();
    $config['framework'] = array(
        'templating' => array(
            'engines'     => array('php', 'smarty', 'twig'),
        'skeleton_module'   => array(
            'path'  => './utils/skeleton_module'
    $config['datasource'] => array(
        'connections' = require __DIR__ . '/datasource.php'
    $config['modules'] = require __DIR__ . 'modules.php';
    return $config;


The configuration shown above is not exhaustive. For a complete listing of the available configuration options please check the sections in the Configuration Reference chapter.

The datasource.yml file

The datasource.yml is where you setup your database connection information.


Because this file may hold sensitive information consider not adding it to your source control system.

  • YAML
                type:   'pdo_mysql'
                host:   'localhost'
                dbname: 'ppi2_skeleton'
                user:   'root'
                pass:   'secret'
  • PHP
    return array(
        'main' => array(
            'type'   => 'pdo_mysql',    // This can be any pdo driver. i.e: pdo_sqlite
            'host'   => 'localhost',
            'dbname' => 'ppi2_skeleton',
            'user'   => 'root',
            'pass'   => 'secret'

The modules.yml file

The example below shows that you can control which modules are active and a list of directories module_paths that PPI will scan for your modules. Pay close attention to the order in which your modules are loaded. If one of your modules relies on resources loaded by another module. Make sure the module loading the resources is loaded before the others that depend upon it.

  • YAML
            - Framework
            - Application
            - UserModule
            module_paths: ['./modules', './vendor']
  • PHP
    return array(
        'active_modules' => array(
        'module_listener_options' => array(
            'module_paths' => array('./modules', './vendor')

The app/views folder

This folder is your applications global views folder. A global view is one that a multitude of other module views extend from. A good example of this is your website’s template file. The following is an example of /app/views/base.html.php:

        <h1>My website</h1>
        <div class="content">
            <?php $view['slots']->output('_content'); ?>

You’ll notice later on in the Templating section to reference and extend a global template file, you will use the following syntax in your modules template.

<?php $view->extend('::base.html.php'); ?>

Now everything from your module template will be applied into your base.html.php files _content section demonstrated above.

The modules folder

This is where we get stuck into the real details, we’re going into the /modules/ folder. Click the next section to proceed.