Why I Deploy Rails Apps with Capistrano in Docker (Yes, Still)

Most Rails devs have moved on to CI pipelines, fancy cloud hooks, or even zero-deploy tools.

So when I tell people I still use Capistrano to deploy all my Rails apps, I get a look—like I just admitted to still using FTP.

But here’s the thing:

I’ve deployed hundreds of times using Capistrano.

And now I do it all inside Docker.

Not only does it work flawlessly, it avoids a whole category of headaches:

• No SSH agent weirdness
• No local Ruby version dependencies
• No flaky CI step failures
• No provisioning a new box every time

If you’re a solo developer or running a small team, this setup might save your sanity.

🧠 Why Not Just Use CI or GitHub Actions?

Because I don’t need to.

My Docker-based Capistrano workflow:

• Works consistently on every project
• Doesn’t rely on CI/CD services
• Deploys over existing installations, with zero downtime
• Avoids manual SSH key forwarding
• Is self-contained, fast, and shareable with collaborators

No CI pipeline. No secrets storage. No cloud runners.

Just a predictable image, and a deploy that just works.

🧱 How It Works

🐳 The Dockerfile (Summary)

This Dockerfile installs all the system dependencies needed to run Capistrano inside a container, bundles your app, and sets up a deploy script as the container's entrypoint.

FROM ruby:3.2.2-bullseye

# Installs system packages like libpq-dev, openssh-client, yarn, etc.
# Creates the working directory
# Installs bundler and installs gems
# Adds a deploy.sh script and runs it

You can build it like this:

docker build -t myapp-deploy -f Dockerfile.deploy.fixed .

The full Dockerfile is available in the free starter kit (link below).

🚀 Running the Deploy

Once built, you can deploy like this:

docker run -it --rm \
  -v $(pwd)/server_key:/app/server_key \
  -v $(pwd)/github_key:/app/github_key \
  -v $(pwd):/app \
  -e DEPLOY_STAGE=production \
  myapp-deploy

This mounts your app directory and private SSH keys into the container so that Capistrano can connect to both the server and your Git repo.

🧰 The Deploy Script (deploy.sh) — Summary

This script configures the SSH environment inside the container, adds GitHub to known hosts, and kicks off the Capistrano deployment.

# Sets up /root/.ssh
# Copies and sets permissions for mounted SSH keys
# Adds github.com to known_hosts
# Writes SSH config for your target server
# Runs: bundle exec cap production deploy

The full script is included in the download below.

📦 Free Starter Kit

I've packaged everything (Dockerfile, deploy script, Capistrano config) into a free downloadable starter kit.

Grab it here → https://realliferails.com/dockerized-deploy-kit/

Includes:

• Dockerfile.deploy.fixed
• deploy.sh
• Example deploy.rb
• README instructions

🤝 Tradeoffs

Let’s be honest:

• This doesn’t use CI. If that’s a dealbreaker for you, no problem.
• Some people dislike the Capistrano DSL. I don’t. It works.
• This method expects you to manage SSH keys carefully—but you are in control, not a black box.

🔧 Why I Stick With It

I use this for every Rails project.

It’s portable, reproducible, and doesn’t get in my way.

Even contractors can deploy safely without polluting their machines or setting up CI pipelines.

🛠 Need Help?

If you’re dealing with flaky deploys, broken staging environments, or SSH key nightmares, I run Rails Rescue Sprints that cover exactly this kind of infrastructure cleanup.

👉 https://realliferails.com/ruby-on-rails-rescue-sprint