Dynamic (runtime) role

[ky]

I use Amazon's EC2 for my production system. Currently I'm writing a
recipe to spawn a new server instance and massage it into a fresh,
clean, staging instance. My recipes all set, except one thing: EC2
provides a dynamic, unpredictable server name (something like
ec2-67-202-12-42.z-1.compute-1.amazonaws.com). I'd like to connect to
this machine thru capistrano (and give it a better dns name, amongst
other things) -- but how?

Roles apparently cannot be set within a task dynamically at runtime --
this message told me so: "/usr/local/lib/ruby/gems/1.8/gems/
capistrano-2.0.0/lib/capistrano/configuration/namespaces.rb:170:in
`role': roles cannot be defined in a namespace (NotImplementedError)"

Has anyone encountered this problem? If so, what solution do you
suggest?

[Michael Bushkov]

Hi,
Actually you can set roles dynamically. There are 2 ways:
1) You can define you role as a block:
set(:myrole) { (fetch(:remote, nil) == nil) ? :local : :app }

The code inside the block can do actually anything.
Then you can use your role in tasks this way:
task :check_app_status, :roles => myrole do

The important thing here is that you must place "set(:myrole)" statement
strictly before the definition of any task that uses "myrole".

2) The dirtier but more dynamic solution:
parent.roles[:myrole] = [] #clearing the role servers list
parent.role :myrole, server_host #appending the hostname to the role

Hope this would help.
--
Cheers,
Michael

[ky]

Thanks for the help -- however, I don't think either of these
solutions will work for my problem.

The first solution dynamically sets a variable to a symbol -- the
symbol can be used to look up statically declared host-roles.
However, I have a dynamic host.

The second solution throws this error: /usr/local/lib/ruby/gems/1.8/
gems/capistrano-2.0.0/lib/capistrano/configuration/connections.rb:
121:in `execute_on_servers': undefined method `host' for
"ec2-67-202-12-42.z-1.compute-1.amazonaws.com":String (NoMethodError).

I could keep hacking, but I figured it'd be wiser to get a Community
Approved Solution (tm).

[Michael Bushkov]

ky wrote:
>
> I could keep hacking, but I figured it'd be wiser to get a Community
> Approved Solution (tm).
>

Yup, that's the option :) Actually maybe the simplest solution for you
will be to place the code that will discover the hostname into the
/etc/capistrano.conf, because it is executed prior to any recipe:
..
.. #discover dynamic host name, put it into 'dhname' variable
..
set :dynamic_host, dhname

and then in one of your recipies you can have the following task definition:
task :check_app_status, :roles => dynamic_host do
..
end

In this case the task's role will be the 'dynamic_host' contents.

>
> The second solution throws this error: /usr/local/lib/ruby/gems/1.8/
> gems/capistrano-2.0.0/lib/capistrano/configuration/connections.rb:
> 121:in `execute_on_servers': undefined method `host' for
> "ec2-67-202-12-42.z-1.compute-1.amazonaws.com":String (NoMethodError).

Sorry, the right variant is the:

arent.roles[:myrole] = [] #clearing the role servers list

parent.role :myrole, Capistrano::ServerDefinition.new(server_host)

--
Cheers,
Michael

[ky]

Thanks Michael.
In the end this worked:

parent.roles[:myrole] =
[Capistrano::ServerDefinition.new(my_staging_name)]

This is definately not part of the api, but at this time its the only
way I've found to make it work. Any cleaner solutions welcome.