Simplified proxy hosts validation and documentation, similar to accessory config

lib/kamal/configuration/docs/proxy.yml

@@ -17,24 +17,16 @@
 # `proxy: true` or providing a proxy configuration.
 proxy:
 
-  # Host
+  # Hosts
   #
   # The hosts that will be used to serve the app. The proxy will only route requests
   # to this host to your app.
   #
   # If no hosts are set, then all requests will be forwarded, except for matching
   # requests for other apps deployed on that server that do have a host set.
+  #
+  # Specify one of `host` or `hosts`.
   host: foo.example.com
-  # If multiple hosts are needed, these can be specified by comma-separating the hosts.
-  host: foo.example.com,bar.example.com
-
-  # Hosts
-  #
-  # The hosts that will be used to serve the app. The proxy will only route requests
-  # to these hosts to your app.
-  #
-  # If no hosts are set, then all requests will be forwarded, except for matching
-  # requests for other apps deployed on that server that do have a host set.
   hosts:
     - foo.example.com
     - bar.example.com

lib/kamal/configuration/validator/proxy.rb

@@ -7,8 +7,8 @@ class Kamal::Configuration::Validator::Proxy < Kamal::Configuration::Validator
         error "Must set a host to enable automatic SSL"
       end
 
-      if config["host"].present? && config["hosts"].present?
+      if (config.keys & [ "host", "hosts" ]).size > 1
-        error "Must use either 'host' or 'hosts', not both"
+        error "Specify one of 'host' or 'hosts', not both"
       end
     end
   end