Passenger Ruby Report App Tutorial

Passenger Ruby Status App Tutorial

**Note: this is a DRAFT of a tutorial that will be moved to **

Passenger Overview

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Tutorial

Login to Open OnDemand, click "Develop" and "My Sandbox Apps (Development)". Click "New Product" and "Clone Existing App". We will be starting with an example status app that displays the output of the ps command.

screenshot

1. Directory name: quota
2. Git remote: https://github.com/OSC/ood-example-ps
3. Check "Create new Git Project from this?"
4. Click Submit

screenshot

Launch the app by clicking the large blue Launch button and in a new browser window/tab you will see the output of a ps command filtered using grep.

screeenshot

The features of this app include:

1. The app uses the custom branded Bootstrap 3 that My Jobs ande ActiveJobs apps use.
2. The navbar contains a link back to the dashboard.
3. On a request, the app runs a shell command, parses the output, and displays the result in a table.

This serves as a good starting point for any status app to build for OnDemand, because

1. the app has the branding matching other OnDemand apps
2. all status apps will do something similar on a request to the app:
   1. get raw data from a shell command or http request
   2. parse the raw data into an intermediate object representation
   3. use that intermediate object representation to display the data formatted as a table or graph

Go back to the Dashboard browser window/tab where the quota details page is displayed. Click the Files button to open this app in the File Explorer. Notice the structure of the app. It is a Ruby Passenger app that uses the Sinatra web framework:

1. config.ru is the entry point for the app (as is for all Ruby Passenger apps)
2. the Gemfile and Gemfile.lock specify the Ruby gem dependencies, and those dependencies are installed in vendor/bundle
3. public/ contains static css and js files. everything under public/ is automatically served up by NGINX
4. views/ contains index.html which is the template for the body of the index page, and the layout.html which contains the erb tag <%== yield %> that is replaced with the rendered contents of index.html

Here is part of the config.ru file that defines a single route for '/':

get '/' do
  # Define your variables that will be sent to the view.
  @title = "Currently Running OnDemand Passenger Apps"
  @command = "ps aux | grep App | grep -v grep"

  # Run the command and capture the stdout, stderr, and exit code as separate variables.
  stdout_str, stderr_str, status = Open3.capture3(@command)

  # Parse the stdout of the command and set the resulting object array to a variable.
  @app_processes = parse_ps(stdout_str)

  # If there was an error performing the command, set it to an error variable.
  @error = stderr_str unless status.success?

  # Variables will be available in views/index.erb
  erb :index
end

This does 3 things:

1. Sets several instance variables for things like the title and the command to run
2. Executes a shell command, calls a helper method to parse the output, and sets the resulting array of structs to an instance variable
3. Renders the views/index.erb which makes uses of the instance variables to render the webpage

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