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I have 20 servers that are in the "web" role. I have a task I need to perform on only one of them as the change affects shared storage. My current solution is a hack to get around this (below). Looking for a better way, I don't have a ton of ruby or cap experience.

task :checkout_project_properties do
    num_runs = 0
    on roles(:web), in: :sequence do
        if num_runs > 0
            abort('Only running on one server.  Exiting')
        end
        execute("checkout-project-properties #{uc_stage} #{repo} #{branch}")
        num_runs += 1
    end
end
Jeff V
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1 Answers1

7

I assume that you are referring to your production configuration, with so many web servers. In this case, your config/deploy/production.rb probably contains many lines like this:

server 'web_1', roles: %w(web)
server 'web_2', roles: %w(web)
server 'web_3', roles: %w(web)
...

Simply make one of these servers primary, so it looks like:

server 'web_1', roles: %w(web), primary: true
server 'web_2', roles: %w(web)
server 'web_3', roles: %w(web)
...

Then change your task so it looks like this:

task :checkout_project_properties do
    on primary(:web) do
        execute("checkout-project-properties #{uc_stage} #{repo} #{branch}")
    end
end
pymkin
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  • Not working for me :'( I've tried with or without the `(:web)`, and other combinations. Might it be because I'm doing an `invoke` instead of an `execute`? – LaurentG Sep 20 '16 at 09:31
  • What can you do if you want to run on any server of any role ? It seems like the `primary` method must take an argument – Cyril Duchon-Doris Feb 18 '20 at 09:43