Git is the one of the best version control system around, and bitbucket offers unlimited free private repos. What’s left is a simple way to deploy to your server every push.

The solution? BitBucket hooks.

Introduction to BitBucket hooks

BitBucket Hooks allow an easy way to trigger scripts after each push . The one we’re looking for today is a POST hook.

A POST hook sends a ‘payload’ of information related to the repository and the git commit, formatted in JSON, as a POST request to a URL we supply. (Instructions for setting up and example payload data by BitBucket).

So, go on and create a script with an obscure and un-guessable name (security through obscurity), for example, deploy-correcthorsebatterystapler.php. Next, make a POST hook on the repo of your choice to call said php script.

What does the deploy script do?

Our script will do four things:

  1. Parse the payload sent by Bitbucket servers.
  2. Check the payload data.
  3. Pull from the remote repository.
  4. Log results.

Note step 3 – Pulling from the remote repository. For that, we’ll need to create a SSH key so that our PHP user can access and modify the remote repo without a password.

Setting up SSH

Who am I?

First, we need to find out who the PHP user is. We could do that through a PHP script that executes whoami in the shell. Run this:

<?php echo exec('whoami'); ?>

Depending on the configuration, you could get apache, www-data, or any other. My PHP user is www-data, and since I’m lazy, I’ll write the post using www-data.

Creating keys for www-data

For creating the keys, we basically need to:

  1. Access the shell as the www-data (Requires sudo).
  2. Create keys.
  3. Add BitBucket.org as host for that key in the config file.

To give commands as any other user, we do sudo -u <username> <command>. So in this case, we’ll do sudo -u www-data.

The first step is to create a SSH key pair. Run sudo -u www-data ssh-keygen -t rsa. That would show the directory where SSH keys are stored for www-data, and, create a key pair. You’ll be prompted for the name and password of the key. I set the name to id_rsa-git, feel free to name it anything; but the password should be blank.

Now, we need to create a config file in www-data‘s SSH directory. A config file tells which host uses what key for SSH access. cd to the SSH directory (mine was /var/www/.ssh) and create file config in that folder.

(You may need to change permissions of .ssh to 0700 for cding in, do that by running sudo chmod 0700 /var/www/.ssh.)

The config file requires two lines:

Host bitbucket.org <more hosts, space separated>  
    IdentityFile <keyname>

My config file looks like

Host bitbucket.org github.com  
    IdentityFile /var/www/.ssh/id_rsa-git

…and you’re done here. Give yourself a pat on the back.

Back to the deploy script

Parsing and verifying the payload

The payload is in JSON, and to use it as a PHP object, we have to decode it.

<?php  
    $payload = '';
    if ( isset($_POST['payload']) ){
        $payload = json_decode($_POST['payload']);
    } else {
        return false;
    }
    $repo = $payload->repository
?>

The above snippet checks if the payload exists, and if it does, sets $payload variable to data from BitBucket. Also set $repo to repository in payload.

Pull from the remote repo

This is simple – we need to run init, then add an origin, and then pull from the origin repo.

To enter a bash command in PHP, we need to use exec().

<?php  
exec('git init && git remote add origin git@bitbucket.org:' . $repo->absolute_url . '.git . && git pull origin master');  
?>

Logging runs

This is the easiest part. Using file_put_contents, we create a log file where times when the script was run are added.

<?php  
file_put_contents('bitbucket-deployment.log', 'Last run on: ' . date('m/d/Y h:i:s a'), FILE_APPEND);  
?>

…and you’re done. Congrats! Read further if you want to add more stuff to your script and want to get tips for debugging.

The final deploy script:

<?php

  $payload = '';
  if ( isset($_POST['payload']) ){
    $payload = json_decode($_POST['payload']);
  } else {
    return false;
  }

  $repo = $payload->repository;

  exec('git init && git remote add origin git@bitbucket.org:' . $repo->absolute_url . '.git . && git pull origin master');

  file_put_contents('bitbucket-deployment.log', 'Last run on: ' . date('m/d/Y h:i:s a'), FILE_APPEND);

?>

Debugging

Echoing the output of shell commands and using demo payload data are two easy ways we can debug.

Demo payload data

<?php  
    $payload = '';
    if ( isset($_POST['payload']) ){
        $payload = json_decode($_POST['payload']);
        file_put_contents('payload.log', $_POST['payload']);
    } else {
        $payload = json_decode(file_get_contents('payload.log'))
        return false;
    }
    $repo = $payload->repository
?>

Put the output of $_POST['payload'] to payload.log, and run a testing push. A new file, payload.log, will be created and you’ll find demo data. Visiting the URL from your web browsers will let you retain and test with actual payload data. You can the use echos for testing, instead of the complicated file_put_contents(). Pretty cool, right?

Output shell command results to the browser

Changing the execution line to this

<?php  
echo exec('git init 2>&1 && git remote add origin git@bitbucket.org:' . $repo->absolute_url . '.git . 2>&1  && git pull origin master 2>&1');  
?>

Will echo the outputs of each command.

2>&1 redirects stderr to stdout, while the echo before exec(...) will print stdout in the browser.

Further reading