“What’s new since the last deploy?”

Managing deployments is one of the trickier aspects of creating software for the web. Several times a week, a project manager will ask the dev team something to the effect of “what’s new since the last deploy?” – if we did a deploy right now, what commits would that include? Fortunately, the tooling around this stuff has never been better (as Tim Bray says, “These are the good old days.”). Easy enough to pull this info via command line and paste a list into Campfire, but if you’re using GitHub and Capistrano, here’s a nifty way to see this information on the website without bothering the team. As the saying goes, teach a man to fetch and whatever shut up.

Tag deploys with Capistrano

The first step is to tag each deploy. Drop this recipe in your config/deploy.rb (original source):

namespace :git do
 task :push_deploy_tag do
 user = `git config --get user.name`.chomp
 email = `git config --get user.email`.chomp

 puts `git tag #{stage}-deploy-#{release_name} #{current_revision} -m "Deployed by #{user} <#{email}>"`
 puts `git push --tags origin`
 end
end

Then throw a after 'deploy:restart', 'git:push_deploy_tag' into the appropriate deploy environment files. Note that this task works with Capistrano version 2 with the capistrano-ext library. For Cap 3, check out this gist from Zachary.

GitHub Tag Interface

Now that you’re tagging the head commit of each deploy, you can take advantage of an (as far as I can tell) unadvertised GitHub feature: the tags interface. Simply visit (or have your PM visit) github.com/<organization>/<repo>/tags (e.g. https://github.com/rails/rails/tags) to see a list of tags in reverse chronological order. From here, they can click the most recent tag (production-deploy-2014...), and then the link that says “[N] commits to master since this tag” to see everything that would go out in a new deploy. Or if you’re more of a visual learner, here’s a gif for great justice:

This approach assumes a very basic development and deployment model, where deploys are happening straight from the same branch that features are being merged into. As projects grow more complex, so must your deployment model. Automatically tagging deploys as we’ve outlined here breaks down under more complex systems, but the GitHub tag interface continues to provide value if you’re tagging your deploys in any manner.