Simple Cluster Management Tool

It may be usefull if Your claster has about 1-10 boxes, and tools like Chef, Puppet, Capistrano are too complex and proprietary for Your needs. It's very easy, there are only a 3 concept - Box, Cluster and Service.

Usage:

• package installation, dependencies, versioning
• process management, start/stop services
• deplyment

It's designed to be used with Virtual File System, Virtual Operation System and Rake, but it's not required, You can use other tools also. For testing purposes it uses Vagrant to test in a local Virtual Machine. If you're going to use Vagrant, you need to install VirtualBox

Core Concepts

• Box - a PC with remote access.
• Service - some abstract thing (a package, running process, app, ...) that operates on 1..n boxes. It can perform install/update/start/stop/.. operations and request other services to perform things it needs.
• Deployment Scheme - defines how services are distributed among boxes.

Deployment Scheme

Let's suppose that we want to deploy our App on a cluster of 3 boxes using the following scheme. Tags are used to define connections (N to M, althouth in example below it's 1 to 1) between Boxes and Services.

Deployment scheme defined via box tags (in config) and service tags, see below.

Boxes

Boxes are defined in config:

handy_scheme:
  'web1.app.com': ['web']
  'web2.app.com': ['web']
  'db.app.com': ['db']

Services

Dependencies are defined by calling another services, it's easy to use and understand and allows high flexibility in configuration.

And, it's 'smart', in sample below the App::deploy method is smart ennought to figure out that it needs the Ruby and MySQL Services and it will call for them to apply before itself.

You can specify that the package should be applied only once (see :apply_once), and use versioning (see :version) - change the version and it will be reapplied.

It supports iterative development and can figure out what services are missing and needs to be applied, You don't have to write all the config at once, do it by small steps, adding one package after another.

Below are our Services:

class Services::Ruby < Service
  tag :web
  version 4
  
  def install
    # it will be called only once, it will be called next time only if You change the version
    apply_once :install do |box|            
      logger.info "installing :#{service_name}"
      box.fake_bash "apt-get install ruby"
    end
  end
end

class Services::Thin < Service
  tag :web
  
  def restart
    logger.info "restarting :#{service_name}"
    boxes.each{|box| box.fake_bash 'thin restart'}
  end
end

class Services::MySql < Service
  tag :db
  def started
    logger.info "ensuring mysql is running"
    box.fake_bash 'mysql start' unless box.fake_bash('ps -A') =~ /mysql/
  end
end

class Services::App < Service
  tag :web

  def install      
    services.ruby.install        
    apply_once :install do |box| 
      logger.info "installing :#{service_name}"
      box.fake_bash "cd #{config.app_path} && git clone app"
    end
  end

  def update
    install        
    logger.info "updating :#{service_name}"
    boxes.each{|box| box.fake_bash "cd #{config.app_path} && git pull app"}
  end

  def deploy    
    update
    logger.info "deploying :#{service_name}"  
    services.my_sql.started
    services.thin.restart
  end    
end

Rake

desc 'deploy to cluster'
task :deploy do
  cluster.services.app.deploy
end

Note: You don't have install services before deployment, the App::deploy will resolve all dependencies automatically and fully configure all boxes from clean state - it will install packages, ensure all needed services are running and only then will start deployment.

Now, type:

$ rake deploy

You'll se something like this:

installing :ruby
   => bash: 'apt-get install ruby'
installing :app
   => bash: 'cd /tmp/cm_example_app && git clone app'
updating :app
   => bash: 'cd /tmp/cm_example_app && git pull app'
deploying :app
ensuring mysql is running
   => bash: 'ps -A'
   => bash: 'mysql start'
restarting :thin
   => bash: 'thin restart'

Deploy one more time, notice now there's no installation of Ruby and App:

updating :app
   => bash: 'cd /tmp/cm_example_app && git pull app'
deploying :app
ensuring mysql is running
   => bash: 'ps -A'
   => bash: 'mysql start'
restarting :thin
   => bash: 'thin restart'

Installation

$ gem install cluster_management

Examples

Clone cluster_management and go to example folder, there are full example. You can do the following:

$ bundle install
$ vagrant init # and wait for the image to be downloaded
$ vagrant up # this will power on the VM
$ rake deploy
installing :ruby to 10.11.12.13
  deleting old version
  building
  configuring
  updating environment
installing :app
updating :app
deploying :app

And voilà! It's done!

You can also see 'real' configuration I use to manage the http://ruby-lang.info site, my_cluster.

Bugs, Suggestion, Discussions

Please feel free to submit bugs and proposals to the issue tab above, or contact me directly.

Contributors

• Alexey Petrushin
• Fernando Mumbach