Deploying with Git

I often rely on Capistrano to deploy web applications. I already talked about this tool in my previous blog. In this article, I am going to describe a simpler approach to deploy simple apps.

When you need to deploy a simple web application on a server, like this blog for instance, there is no need to use Capistrano or Fabric. We mainly want a way to copy a set of files and one could rely on rsync or scp… How boring!

An alternative is to rely on Git, assuming you are using it. But how?

The first step is to configure the local repository by adding a new remote:

git remote add -t master production ssh://<server>/path/to/project_prod

The -t <branch> option allows to track a given branch instead of all branches. You can add more remotes if you want, like a testing remote for instance:

git remote add testing ssh://<server>/path/to/project_test

To deploy the application to production, run:

git push production

To deploy the application to a testing environment, run:

git push testing <branch>

At the moment, you can push your code to your server but it won’t deploy your changes. We need to configure Git. First, add the following lines to the .git/config file:

[receive]
    denyCurrentBranch = false

This allows to push code to the current branch, which is important to deploy your new changes. Old Git versions don’t need to set this parameter by the way.

Then, create and enable a post-receive hook with the following content:

#!/usr/bin/env bash

SUBJECT="Deploy successful"
BODY="You've successfully deployed the branch:"

while read oldrev newrev ref
do
    branch=`echo $ref | cut -d/ -f3`

    if [ "$branch" ] ; then
        cd ..
        env -i git checkout $branch
        env -i git reset --hard

        EMAIL=`env -i git log -1 --format=format:%ae HEAD`
        BODY="$BODY $branch."

        echo "$BODY" | mail -s "$SUBJECT" "$EMAIL"
    fi
done

This script updates the working tree after changes have been pushed, and send an email to the last committer. Keep in mind that it always deploys the last branch you push.

The important part is:

cd ..
env -i git checkout $branch
env -i git reset --hard

Feel free to “decorate” these three lines as you wish.

For example, for the production environment (or because you are using a Git Branching Model), you should modify the previous script to make sure that you only deploy the master branch:

    if [ "$branch"  == "master" ] ; then
        cd ..
        # env -i git checkout $branch
        env -i git reset --hard

        # Send an email
    fi

You’re done! Each time you’ll execute git push production, you’ll deploy your application to your production environment. Easy. Fast. Powerful.