Cap Blue Green Deploy

Blue-Green deployment solution for Capistrano, using symbolic links between releases.

Blue Green Concept

Learn more about Blue Green Deployment with Martin Fowler

Presentations about this gem and the concept:

Introduction

Cap Blue Green Deployment is a non canonical Blue Green solution, based on symlinks. Instead of having blue and green, we have pre and live. Pre is always validation environment and live it's production environment.

You can do as many deploys as you need to pre without affecting your live env. Changing symlinks you can easily put your code from validation to production environment.

Prerequisite

Capistrano 2 (Capistrano 3 coming soon)

Installation

Add this line to your application's Gemfile:

gem 'cap_blue_green_deploy'

And then execute:

$ bundle

Or install it yourself as:

$ gem install cap_blue_green_deploy

And then, require the gem script under your capistrano configuration file (Capfile, deploy.rb, ...):

require 'cap_blue_green_deploy'

Usage

Understanding the deploy folder:

current: Pre environment. Used to test and validate your application.
current_live: Live environment. Your production access goes here. This dir name can be customized in custom variables, see below
previous_live: Last live release. Used to do the rollback action of current_live. This dir name can be customized in custom variables, see below

Deploy Commands:

Going to Pre cap deploy:blue_green:pre

This command is an alias for cap deploy default task. It will run the deploy process and create the current release
Going to Live cap deploy:blue_green:live

This command will change symlinks of current_live dir to use the same release path of current dir. And also create the previous_live symlink to track the last current live release used.
Rolling back cap deploy:blue_green:rollback

This command will change the current_live symlink to use the same destination of previous_live symlink.
Cleanup cap deploy:blue_green:cleanup

This is the same behavior of the default capistrano cleanup deploy:cleanup, but the current, current_live and previous_live releases will be preserved and not removed.

This lib automatically rewrite the default deploy:cleanup to use this new cleanup function.

Don't forget that you need to add the cleanup callback manually in your capistrano file: after "deploy:update", "deploy:cleanup"
Custom Variables

You can change the default values by overwriting them in your capistrano file. The default values are:
- keep_releases: 5
- blue_green_live_dir: "current_live"
- blue_green_previous_dir: "previous_live"

How to Play

Custom Variables used

set :keep_releases, 2
set :blue_green_live_dir, "current_live"
set :blue_green_previous_dir, "previous_live"

1. Starting with clean server

2. Running cap deploy:setup to prepare the server

3. Running cap deploy three times to populate the release folder (cleanup code removes one old release)

4. Going to live cap deploy:blue_green:live (current_live dir will be created. No changes in releases dir)

5. Running two more deploy with cap deploy (current_live will not change. Cleanup remove one old release.)

6. Going to live again with cap deploy:blue_green:live (At this time, previous_live will be created, targeting the current_live release before change it. No changes in releases dir)

7. Something goes wrong... Rollbacking with cap deploy:blue_green:rollback (The current_live will change to target the same release of previous_live. No changes in releases dir)