Allow deployment in a single role

[wenderjean]

Hi guys!

So, by the time I'm writing this suggestion I'm trying to test a specific configuration for Sidekiq and to do that I need to deploy a new instance, no surprise up here :) but... It seems like Kamal does not allow us to run a commands like these ones:

kamal deploy -P -d production --version=xyz --roles=worker
kamal redeploy -d production --version=xyz --roles=worker

Initially I assumed it was a bug considering when the command executes, the error I receive is that Kamal cannot find .kamal/env/roles/app-web-production.env but after reading this DHH's comment here I'm not that sure if this should even be possible assuming it could open up room for non-web applications deployment.

What do you guys think about this feature? The scenario itself seems doable.

[morgoth]

I got the same error, vide #709