Using capistrano to deploy from different git branches

I am using capistrano to deploy a RoR application. The codebase is in a git repository, and branching is widely used in development. Capistrano uses deploy.rb file for it's settings, one of them being the branch to deploy from.

My problem is this: let's say I create a new branch A from master. The deploy file will reference master branch. I edit that, so A can be deployed to test environment. I finish working on the feature, and merge branch A into master. Since the deploy.rb file from A is fresher, it gets merged in and now the deploy.rb in master branch references A. Time to edit again.

That's a lot of seemingly unnecessary manual editing - the parameter should always match current branch name. On top of that, it is easy to forget to edit the settings each and every time.

What would be the best way to automate this process?

Edit: Turns out someone already had done exactly what I needed:

This morning I had occasion to deploy a branch of a git repository to a staging server but hadn’t the foggiest idea how. A quick search through the capistrano source code revealed that I could use set :branch "branch_name" in my deploy script. I tried it and it worked. I then figured I would need to make a similar change across all my branches. Of course, I’m a lazy sod and wondered if there wasn’t a better way.

If you’re not familiar with git, the output of the git branch command is a list of branches with an asterisk marking the one currently checked out on your local machine. For example:

> git branch
* drupal_authentication
fragment_caching
master

So, I figured, what if I just parsed the output and searched for the branch marked as current:

set :branch, $1 if `git branch` =~ /\* (\S+)\s/m

Now I’m able to deploy whatever branch is current on my local machine from a single, shared, deploy script.

This works with Capistrano >= 3.1:

add this line to config/deploy.rb:

set :branch, ENV['BRANCH'] if ENV['BRANCH']

and then call capistrano with:

cap production deploy BRANCH=master

This solution works with Capistrano < 3.1:

# call with cap -s env="<env>" branch="<branchname>" deploy

set :branch, fetch(:branch, "master")
set :env, fetch(:env, "production")

Using Capistrano 3.1.0+, none of these were working for me anymore. Instead, according to their commented instructions:

   ask :branch, proc { `git rev-parse --abbrev-ref HEAD`.chomp }

But, you don't want to use ask or it will prompt you. Instead you should use set. HEAD is the top most branch; 'edge' as it's called. If you want a different branch, replace HEAD with your branch name, eg: master, staging, etc.

To conclude with examples, in /config/deploy/production.rb, you might include this line:

   set :branch, proc { `git rev-parse --abbrev-ref master`.chomp }

...or

   set :branch, proc { `git rev-parse --abbrev-ref HEAD`.chomp }

btw, HEAD is the default setting, so no need to really state that in file. Might be used better in a /config/deploy/edge.rb.

In /config/deploy/staging.rb, you might include this line:

   set :branch, proc { `git rev-parse --abbrev-ref staging`.chomp }

...or

   set :branch, proc { `git rev-parse --abbrev-ref test`.chomp }

You get the idea!

I hope these examples help future users of capistrano (^_^)

I can confirm that the below still works in Cap 3.11.0 13/10/18 as well as Cap 2:

In deploy.rb / stage.rb:

set :branch, ENV['BRANCH'] || 'develop'

On the command line:

cap deploy BRANCH=featurex

This gives you a default branch (which could be different for different environments), and the ability to change branches when you want.

With multistage, it's actually now:

cap production deploy -s branch=my-branch

The previous post syntax does not work in my environment

Alternatively you could structure it from the command line where you have a default branch and environment and also you are able to pass parameters to the cap call which could include the environment and the branch to use. This could be a branch that is explicitly passed or you could have a parameter which would indicate current branch as described in the link you listed.

#call with cap -S env="<env>" branch="<branchname>" deploy
...

# Prevents error if not parameter passed, assumes that default 'cap deploy' command
# and should deploy the master branch to the production server
set(:env, ‘production’) unless exists?(:env)
set(:branch, ‘master’) unless exists?(:branch)

if !env.nil? && env == "production"
   role :web, "production_ip_address"
else   # add more as needed 
   role :web, "development_ip_address"
end

if !branch.nil? && branch == "current"
   set :branch, $1 if `git branch` =~ /\* (\S+)\s/m
elsif !branch.nil?
   set :branch, branch
else   # add more as needed 
   set :branch, "master"
end
...

Code example borrowed heavily from here