Nihal Singh

It had been a while since I had been using a server to host the website for WnCC. With a lot of development happening around, updating and testing changes on the server, had become a requirement. Having built the site in Jekyll, I required to shift the contents of _site from my local machine to /var/www/html on the server, after every build. I had been following the simple, standard method of using scp, for a long time. Copying all the content from _site to /var/www/html was now becoming inefficient (as I copied all the files in the folder all over again), took a lot of time as the site started expanding with more multimedia content, and required a long terminal command too. I could have used a probably more efficient way of SSHing into the server, pulling from the git repository and copying the contents of the _site folder into /var/www/html. But this would have been tedious too, and probably could have been made easier with a script. Nevertheless, it would have required me to SSH into the server, and atleast a couple of terminal commands.

Discovering Github Webhooks

Enter webhooks. Webhooks allow one to set up an integration with their github repository to listen for one or more events. Whenever such an event occurs, Github sends a HTTP POST payload to the webhook’s configured URL. An event can occur with the creation of an issue, a push to the server or be triggered whenever a repository is starred, forked etc. Webhooks can be used to do a lot of things. I have used a webhook, in this example for the quite general purpose of setting up an auto-deplow on my server.

Github provides a quite comprehensive guide about how to set up a webhook to the local host which is connected to the web using ngrok. I followed the guide and replicated similar steps on my server to get my webhook configured to send a HTTP POST payload to the server.

Using Sinatra

I used Sintara to create a simple web framework which would receive a HTTP POST made to the configured server URL, and run a small shell command. Having written this small piece of code, I could now reflect all changes made in the repository on the website, everytime a push is made to the repository. The following code renames the html folder inside /var/www/ to _site and performs a git pull inside /var/www and later renames it back to html. This is done as the built site lies inside the _site folder of the repository. I

# hook.rb
require 'sinatra'
require 'json'

set :bind, '0.0.0.0'

post '/payload' do
  #push = JSON.parse(request.body.read)
  #puts "I got some JSON: #{push.inspect}"
  output = `mv html _site ; git pull origin master; mv _site html`
  p output
end

Running a ruby hook.rb -o 0.0.0.0 will give a message like Sinatra/1.4.4 has taken the stage on 4567.... Making a POST request on http://IP:4567/payload, will now trigger the shell command in the above script. (-o 0.0.0.0 and set :bind, '0.0.0.0' allows access from networks other than localhost)

Note: You may have to enable the port if you are using a firewall on your server. A simple sudo ufw allow 4567 should do it.

However this session of Sinatra will close as soon as you CTRL+C out of it or logout. To keep such an instance running even after logout you could try

nohup sudo ruby hook.rb -o 0.0.0.0 &

This would put the Sinatra process in background and keep it running even after you have logged out.

I did not know about github webhooks earlier and this was an interesting find. The above was a quick setup for automation. If you know a way in which I could improve it, do let me know in the comments.

Till next time!