Ruby tools a pipeline runs

Why so many tools are Ruby

A pipeline is a list of commands, and several of the commands it runs are Ruby programs. That is why a Ruby job on a CI runner is often not about Rails at all: the runner installs Ruby because one of the tools needs it.

The four below appear in real pipelines often enough to recognise:

• Fastlane builds and releases mobile apps; it is the usual way an iOS or Android release runs from CI.
• Jekyll builds static sites from Markdown, so its build step is a Ruby command.
• Chef configures servers; its recipes are Ruby code and its chef-client runs on the machine being configured.
• Vagrant starts development virtual machines from a Vagrantfile, which is Ruby.

The same list explains why a container image for a build job sometimes carries Ruby even when the project is not Ruby: the tool that builds the artifact is.

Ask RubyGems what is current

The gem command can query the index without installing anything. The --exact flag keeps the answer to one gem:

gem list --remote --exact fastlane

fastlane (2.241.2)

gem list --remote --exact jekyll

jekyll (4.4.1)

That is a useful first step when a pipeline pins a tool version: the number on the remote is what a new install would pick today, and the difference from the pin is the reason a build changed without a commit.

What each one does in a pipeline

Fastlane runs a lane, a named sequence of build and upload steps, and the pipeline calls it as one command. Jekyll builds the site into a folder that the deploy step copies. Chef runs at the end of a deploy to put the machine into the declared state. Vagrant is a developer tool; it rarely runs in a pipeline, but a pipeline that tests it needs a hypervisor.

Each tool is a gem, so each one arrives the same way as minitest or rake. The difference is what a failure means: a failed Jekyll build is a broken page, a failed Chef run is a half-configured server, and both are worth stopping the pipeline for.

What to watch for

Pin the version of a tool that runs in the pipeline. Fastlane in particular changes its output and its lanes often, and an unpinned tool turns a green release into a red one without a line of your code changing.

Install the tool in the job that needs it, not in the project bundle, unless the project really depends on it. A linter belongs in the Gemfile; a deployment tool usually does not.

Next: A pipeline for a CLI gem

Article author: Arthur Isaev