Invoking a capistrano task on another environment - ruby

Question

I am trying to create tasks that sync from my production/staging environments to a local vagrant box.
I am hoping for a command like this: cap vagrant sync_production_database which would perform a database dump on the remote server, download it, and then import it on the vagrant box. Unfortunately, I can't find a way to execute a capistrano task on another environment.
I have my environments set up like so:
config
├── deploy
│   ├── production.rb
│   ├── staging.rb
│   └── vagrant.rb
└── deploy.rb
And here is an example of what I am trying to accomplish:
desc 'sync database'
task :sync_production_database do
# executed on remote server
# this is obviously not working
on(:production) do |host|
# dump database and download it
end
# executed on vagrant box
on roles(:web) do |host|
end
end

Answer 1

First, I think it is better to use the stage parameter of the cap command to designate the remote stage servers rather than your local stage servers. This means your command assumes :vagrant as always being the local stage.
Then if vagrant stage servers have a role which the remote servers don't have, you can execute different tasks on each stage via the following:
# Assuming the following stage definitions in deploy/production.rb and deploy/vagrant.rb respectively
server 'production.example.com', roles: %w{web app}
server 'vagrant.local', roles: %w{web localhost}
# the following will execute tasks on each host
desc 'sync database'
task :sync_database do
# executed on remote server(s)
on roles(:app) do |host|
# dump database and download it
end
# Load the servers in deploy/vagrant.rb
invoke(:vagrant)
# executed on vagrant box server(s)
on roles(:localhost) do |host|
# Create database and load dump from remote
end
end
This works because roles(...) returns all servers loaded with the given role and since each stage has a unique role, you can retrieve only what servers you want by specifying their respective role.
Normally, without invoke(:vagrant), roles(:localhost) in the example above wouldn't return anything since Capistrano only loads the servers defined in the given stage by default. To get around this, you can force load servers in your vagrant stage using invoke(:vagrant). So then, roles(:app) returns the servers for the given stage and roles(:localhost) returns your vagrant servers.