Issue with :hosts - ruby

Question

I have a Capfile for Multistage deploys that needs to deploy the code to one server (NFS) and finally restart several application servers. Roles can therefore not be used easily since application servers do not need to be used for deploy:update_code. I have come up with something that might work, but have a issue that needs to be resolved.
application_servers = nil
task :production do
role :nfs, "nfs.someserver.net"
application_servers = "app.someserver.net"
end
task :staging do
role :nfs, "nfs-staging.someserver.net"
application_servers = "app-staging.someserver.net"
end
desc "tail resin logs #{resin_logs}"
task :tail, :hosts => application_servers do
puts("Server is:"#{application_servers})
stream "tail -f #{resin_logs}"
end
And when running:
#$ cap staging tail
* executing `staging'
* executing `tail'
Server is:app-staging.someserver.net
* executing "tail -f /log/resin/*.log"
servers: ["nfs-staging.someserver.net"]
[nfs-staging.someserver.net] executing command
tail: cannot open `/log/resin/*.log' for reading: No such file or directory
tail: no files remaining
command finished
failed: "sh -c 'tail -f /log/resin/*.log'" on nfs-staging.someserver.net
When printing value of application_servers in task tail it says "app-staging.someserver.net", but the value used in :hosts => application_servers is empty (which is why it uses the role nfs instead).
Why does the variable application_server have two different values? Is it scope issue? I have tried with global ($) and that does not work as well.

Answer 1

Solved the issue just by changing from using :hosts to :roles on application specific task and added a new role. The key feature is to use no_release so that the code is not deployed to application servers. We only want to restart resin instance on those machines.
task :production do
role :nfs, "nfs.someserver.net"
role :application, "app.someserver.net", :no_release => true;
end
task :staging do
role :nfs, "nfs-staging.someserver.net"
role :application, "app-staging.someserver.net", :no_release => true;
end
desc "tail resin logs #{resin_logs}"
task :tail, :roles => application_servers do
puts("Server is:"#{application_servers})
stream "tail -f #{resin_logs}"
end