Has a Go CLI been considered for Kamal?

[gregjotau]

We run Kamal in production and like the model: config/deploy.yml, Docker, and kamal-proxy for zero-downtime switchover. This is not a complaint about that design.

The part that has been expensive for us is the Ruby CLI itself. Kamal is a control-plane tool (SSH + docker + proxy deploy). Almost all of the time in a deploy is Docker. Almost all of the startup cost is MRI + ActiveSupport + Thor + SSHKit, paid on every kamal invocation, including kamal version and kamal app logs.

On a current Mac:

• require "active_support/all" alone is 256 ms
• Kamal then still has to load Thor, SSHKit, net-ssh, dotenv, zeitwerk
• Installing Kamal means installing Ruby plus those gems (tens to hundreds of MB)

We tried rewriting the CLI we actually use in Go, speaking the same on-server protocol (container names, labels, .kamal env files, lock dirs, docker exec kamal-proxy kamal-proxy deploy …). Result:

• 4.1 MB static binary, Go 1.27, CGO_ENABLED=0
• 3 ms to run gamal version
• Same config/deploy.yml (including destination overlays)
• Skips SSH entirely when the target IP is local (our deploys run on the app host and Kamal still SSHKit'd to itself)
• docker login --password-stdin instead of putting the registry password on the command line

Repo: https://github.com/beint-no/gamal

It is not feature-complete Kamal. We did not port accessories, secret-manager adapters, remote/cloud/pack builders, asset bridging, error pages, ERB, or the 1.x Traefik upgrade. Those are not in our configs. The point of publishing it is the measurement, not a claim of parity.

Why bring it here

kamal-proxy is already Go. The remaining Ruby is the orchestrator. That job is a good fit for a static binary: one file on a laptop or a server, no gem boot, no SSHKit, no ActiveSupport. A future Kamal could keep the YAML, the proxy, and the Docker labels, and change only the CLI language.

Rewrites are costly and I am not asking anyone to throw away 2.x. I am asking whether a Go CLI has been considered for Kamal 3, or as an official alternative implementation of the same protocol. Happy to be told the Ruby CLI is a deliberate product choice — then this is just a data point.

Happy to answer questions about what we implemented, what we skipped, and how the protocol mapping was verified.

[gregjotau]

We switched to Gamal for all our apps now. Just a few shot experiment, but seems like a no-brainer to implement for our flow! Implemented just what we needed, and everything is faster.

Kamal is still a great project and we still use the proxy though!