[Capistrano] Re: Dynamic (lazy) Roles

[Jamis Buck]

David,






- Jamis

On Jan 11, 2008, at 3:23 PM, David Masover wrote:

Interesting suggestion. I would definitely consider adding something like that to cap. If anyone were to write up a patch and attach it to a ticket at dev.rubyonrails.org, I'd look it over. In the meantime, you can probably work around it by using the :hosts key, instead of roles, and then using procs to return the exact hosts you want. It's more work, and it would probably wind up duplicating some of what roles give you, but then you don't have to wait for a patch. :)

Thanks, I didn't know about that.

However...  I'm looking for something more like this:

role :foo, do
...
end
task :bar, :roles => :foo
...
end



task :baz, roles => :foo
...
end
task :yetAnotherTask, roles => :foo
...
end
task :mixAndMatch, roles => :foo, :bar
...
end



On 1/11/08, Jamis Buck <[EMAIL PROTECTED]> wrote: David,

Perhaps I'm not understanding what you're mean, but the current
version of Capistrano allows you to do things like this:

   task :foo, :roles => defer { something_that_computes_roles } do
   end

The "defer" method is just an alias for lambda that Capistrano adds.
The block there just needs to return the name of a role (or an array
of role names). That block is then evaluated at the moment that the
task is run.

- Jamis

On Jan 11, 2008, at 1:29 PM, David Masover wrote:

>
> Working on a way to use Capistrano to deploy to ec2. I know about

> IDs anywhere -- particularly as Capistrano itself will eventually be
> creating those itself.
>
> The first roadblock was: I can use variables-as-blocks to define
> things like the list of current instances, the latest instance, etc.

> isn't going to change over the course of a single invocation of cap,
> unless I change it myself.)
>

> the results of ec2-describe-instances (and probably other things as
> well). So, I needed dynamic roles.
>
> I'm completely new to the Rails and Capistrano community, so I'm not

> Here's the hack I have so far:
>
> Capistrano::Configuration::Roles.module_eval do
>       alias_method :orig_role, :role
>       def role(which, *args, &block)

> value or a block"
>               end
>               if block_given? then
>                       which = which.to_sym
>                       @roles[which] = block
>               else
>                       # I apologize for this one-liner

> Capistrano::ServerDefinition.new(item) : item})
>               end
>       end
> end
>
> Capistrano::Configuration::Servers.module_eval do
>       alias_method :find_servers_orig, :find_servers
>       def find_servers(options={})

>
>               if hosts.any?
>                       hosts.uniq
>               else

> self.roles.keys)
>                       roles.each { |role|
>                               target = self.roles [role]
>                               if target.respond_to?(:call)

>                                       }
>                               end
>                       }
>                       find_servers_orig(options)
>               end
>       end
> end
>
>




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That's actually what I implemented in what I sent in, because I couldn't find it. Can "defer" work in a similar way? Because it also allows: Basically, it's not that I don't know which roles I want ahead of time. It's that I have a role that I do know about, very specifically (could be :web, :files, etc), but that I don't necessarily know which servers it will use. > Capsize, but decided that I didn't want to hardcode image and instance > (Variables, not functions or tasks, because I figure that information > But I cannot define roles-as-blocks, and I want to find roles out from > sure what style conventions I should use, where to send patches, etc. > if !block_given? && args.empty? || block_given? && ! args.empty? > raise ArgumentError, "you must specify exactly one of either a > orig_role(which, args.map{|item| String === item ? > hosts = server_list_from(ENV['HOSTS'] || options[:hosts]) > roles = role_list_from(ENV['ROLES'] || options[:roles] || > self.roles[role] = target.call.map { |server| > String === server ? ServerDefinition.new(server, {}) : server

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