ruby - Capistrano: create tasks with roles did not work -

i try create tasks different roles :

namespace :foo   task :mytasks, :roles => [:a, :b,]     task_a     task_b   end    task :task_a, :roles => :a     run 'echo a'   end    task :task_b, :roles => :b     run 'echo b'   end end 

when execute 'mytasks' here result :

$ cap -n roles=b foo:mytasks   * 2013-03-01 16:59:14 executing `foo:mytasks'   * executing "echo a"   * executing "echo b" 

all tasks executed, why ?

capistrano roles intended associate given server (or multiple servers) particular function, such saying "machine-a" web server while "machine-b" database server, useful because tasks need performed on machines.

so roles not intended way conditionally select machine(s) run tasks on @ time when running capistrano, select tasks should run on machines.

there is, however, capistrano feature called multistage may you're looking for. allows specify different sets of servers (and associate them different roles) based on "stage" you're deploying to. have a , b stages, each separate sets of servers, deploy using:

cap foo:mytasks cap b foo:mytasks