I’ve been working on a project involving long-running, resource-intensive batch jobs in Node. At first, when my needs were simpler, I used Heroku to run these jobs. It was great, but eventually, the price:performance ratio offered became a little too unwieldy, and I chose to make a move from Heroku to DigitalOcean.

Almost immediately, I was impressed. In just a short while, I was up and running these jobs with little issue. But there was one challenge I had yet to work out: setting up some sort of deployment process to get the code from my Git repository to my droplet. I was spoiled with Heroku. They make that part of the job incredibly hassle-free. But thankfully, when I made the move to DO, my needs were relatively straightforward:

  • On a git push, I wanted my code to be copied to my droplet.
  • On that same push, I wanted to npm install the dependencies in my package.json.
  • I wanted the option to control which branches would trigger a deployment to that droplet.

As it turned out, the setup was less complicated than I had been expecting. A single Git hook and a little local configuration meet all the needs noted above. This post is basically me backing up and documenting all that I pieced together from experimenting and Googling. Note that I’m not gonna get into the weeds of configuring a DigitalOcean or any other VPS. For the purposes of what I’m showing off here, just make sure you have a SSH access to your droplet, and that Git’s installed on it.

Configure a Remote Repository on Your Droplet

First, create a bare repository on your droplet. A bare repository is one created without a working tree and used solely for sharing code — not working with it. We’ll only be pushing to this repository, so --bare is the way to go.

For this example, kick this of by ssh-ing into your droplet, creating a neat-app-repo directory, and initializing that repository.

ssh user@your-ip-address
cd /home
mkdir neat-app-repo
cd neat-app-repo
git init --bare

Create a post-receive hook file inside your newly created repository. If you’re unfamiliar with them, catch up. In short, this hook will allows to do something after code has been received by the repository on the droplet (ie. when we do a git push). In our case, all we want to happen after our code is received is for it to be moved to a different directory and its dependencies installed.

If you cd into your neat-app-repo/hooks directory (this is one of the directories created when you initialized the bare repository), you should see a long list of *.sample Git hooks. While you’re there, create a new post-receive hook:

touch post-receive

And paste the following bones in there:

#!/bin/bash

while read oldrev newrev ref
do
    # We gonna do stuff. 
done

That’s a bash while read loop with three parameters:

oldrev - The SHA for the previous commit in the pushed branch.

newrev - the SHA for the new commit in the pushed branch.

ref - the Git reference of the branch just pushed. Example: refs/heads/master

Inside of that block, we’re free to do whatever we want, like copy the branch that was just pushed to a different directory:

#!/bin/bash

+# Location of our bare repository.
+GIT_DIR="/home/neat-app-repo"
+
+# Where we want to copy our code.
+TARGET="/home/neat-app-deployed"

while read oldrev newrev ref
do
-   # We gonna do stuff.
+   # Neat trick to get the branch name of the reference just pushed:
+   BRANCH=$(git rev-parse --symbolic --abbrev-ref $ref)
+
+   # Send a nice message to the machine pushing to this remote repository.
+   echo "Push received! Deploying branch: ${BRANCH}..."
+
+   # "Deploy" the branch we just pushed to a specific directory.
+   git --work-tree=$TARGET --git-dir=$GIT_DIR checkout -f $BRANCH
done

After saving that, a couple more steps are required before it’s actually usable:

  1. Make sure that hook is executable. If you skip this, you’ll get a The 'hooks/post-receive' hook was ignored because it's not set as executable error when you push from your machine.
chmod +x post-receive
  1. Make sure the target directory actually exists. If it doesn’t, you’ll get another error.
mkdir /home/neat-app-deployed

Now, for testing purposes, open up the repository on your local machine and set the origin to where your bare repository is located on your droplet.

git remote add origin root@YOUR_IP_ADDRESS:/home/neat-app-repo

Make an arbitrary commit and give it a git push. If successful, you should see something like this.

remote: Push received! Deploying branch: master...
remote: Switched to branch 'master'

Now, let’s (optionally) limit new deployments to specific branches. If you make a new branch and push it to your droplet, you’ll see it deploys successfully, just as if you were on master. Probably less than ideal, so let’s modify our hook to deploy only when the master branch is pushed.

#!/bin/bash

# Location of our bare repository.
GIT_DIR="/home/neat-app-repo"

# Where we want to copy our code.
TARGET="/home/neat-app-deployed"

while read oldrev newrev ref
do
    # Neat trick to get the branch name of the reference just pushed:
    BRANCH=$(git rev-parse --symbolic --abbrev-ref $ref)

+    if [[ $BRANCH == "master" ]];
+    then
        # Send a nice message to the machine pushing to this remote repository.
        echo "Push received! Deploying branch: ${BRANCH}..."

        # "Deploy" the branch we just pushed to a specific directory.
        git --work-tree=$TARGET --git-dir=$GIT_DIR checkout -f $BRANCH
+    else 
+       echo "Not master branch. Skipping."
+    fi
done

Gr8! Now, since my project was in Node, I needed to set up one final thing: run npm installon each deployment. In my case, nvm is in charge of specifying which version of Node I run, so updating my hook looks like this:

#!/bin/bash

# Location of our bare repository.
GIT_DIR="/home/neat-app-repo"

# Where we want to copy our code.
TARGET="/home/neat-app-deployed"

while read oldrev newrev ref
do
    # Neat trick to get the branch name of the reference just pushed:
    BRANCH=$(git rev-parse --symbolic --abbrev-ref $ref)

    if [[ $BRANCH == "master" ]];
    then
        # Send a nice message to the machine pushing to this remote repository.
        echo "Push received! Deploying branch: ${BRANCH}..."

        # "Deploy" the branch we just pushed to a specific directory.
        git --work-tree=$TARGET --git-dir=$GIT_DIR checkout -f $BRANCH
    else 
        echo "Not master branch. Skipping."
    fi

+   # Source nvm to make it available for use inside this script.
+   . $HOME/.nvm/nvm.sh
+    
+   # Use the LTS version of Node.
+   nvm use --lts
+   
+   # Navigate to where my deployed code lives. 
+   cd /home/neat-app-deployed
+
+   # Install dependencies in production mode.
+   npm install --production
done

And with that, pushing to my droplet will now deploy my code exactly where I want it, as well as install the dependencies it needs to run.

Configure Your Local Repository for Easier Deployments

When I first got this all set up, I assumed that if I wanted to push my code up to a remote GitHub repository and deploy it to DO simultaneously, I’d need to create two remotes and push them separately. Then I saw this tweet:

One push, two destinations. And with our post-receive hook only deploying pushes to the master branch, this is a good balance of efficiency and safety for our workflow.

Admittedly, configuring my Git remotes locally was a little weird, but working it all out eventually came to this. Note: this assumes you already had the DO droplet set as your origin.

# Change the `fetch` URL, so we always pull code from GitHub.
git remote set-url origin git@github.com:alexmacarthur/neat-app.git

# Re-add `push` URLs, so that we push to GitHub AND DigitalOcean.
git remote set-url --add --push origin root@YOUR_IP_ADDRESS:/home/neat-app-repo
git remote set-url --add --push origin git@github.com:alexmacarthur/neat-app.git

In the end git remote -v returns this:

origin  root@YOUR_IP_ADDRESS:/home/neat-app-repo (fetch)
origin  git@github.com:alexmacarthur/neat-app.git (push)
origin  root@YOUR_IP_ADDRESS:/home/neat-app-repo (push)

With that configured, a simple git push sends your code to two separate remotes, saving you seconds per day, perhaps.

Expect Gotchas

While it might be conceptually straightforward, working through the details of all this was periodically frustrating for me, especially since it was my first time pulling off such a thing. That said, give yourself a little grace in dealing with the gotchas that will inevitably come up. Hopefully what you read here will help alleviate the pains of the process even just a little bit. If that’s true, writing this all out was worth it.