Rename roles

Allow roles to be renamed without having to manually stop the old
containers.

If you have config like:

```
servers:
  jobs:
    hosts:
      - vm3
```

And you want to rename `jobs` to `workers`, you can do:

```
servers:
  workers:
    previously:
      - jobs
    hosts:
      - vm3
```

And the deployment will take care of stopping the old "jobs" containers.

Once deployed you can remove the `previously` key.

lib/kamal/cli/app/boot.rb

@@ -11,12 +11,12 @@ class Kamal::Cli::App::Boot
   end
 
   def run
-    old_version = old_version_renamed_if_clashing
+    old_version, old_app = old_version_renamed_if_clashing
 
     start_new_version
 
     if old_version
-      stop_old_version(old_version)
+      stop_old_version(old_version, old_app)
     end
   end
 
@@ -41,7 +41,13 @@ class Kamal::Cli::App::Boot
         execute *app.rename_container(version: version, new_version: renamed_version)
       end
 
-      capture_with_info(*app.current_running_version, raise_on_non_zero_exit: false).strip.presence
+      [ role, *role.previous_roles ].each do |old_role|
+        old_app = KAMAL.app(role: old_role)
+        old_version = capture_with_info(*old_app.current_running_version, raise_on_non_zero_exit: false).strip.presence
+        return [ old_version, old_app ] if old_version
+      end
+
+      nil
     end
 
     def start_new_version
@@ -51,7 +57,7 @@ class Kamal::Cli::App::Boot
       Kamal::Cli::Healthcheck::Poller.wait_for_healthy(pause_after_ready: true) { capture_with_info(*app.status(version: version)) }
     end
 
-    def stop_old_version(version)
+    def stop_old_version(version, app)
       if uses_cord?
         cord = capture_with_info(*app.cord(version: version), raise_on_non_zero_exit: false).strip
         if cord.present?

lib/kamal/commands/app.rb

@@ -3,7 +3,7 @@ class Kamal::Commands::App < Kamal::Commands::Base
 
   ACTIVE_DOCKER_STATUSES = [ :running, :restarting ]
 
-  attr_reader :role, :role
+  attr_reader :role
 
   def initialize(config, role: nil)
     super(config)

lib/kamal/configuration.rb

@@ -71,7 +71,9 @@ class Kamal::Configuration
 
 
   def roles
-    @roles ||= role_names.collect { |role_name| Role.new(role_name, config: self) }
+    @roles ||= role_names.collect do |role_name|
+      Role.new(role_name, config: self, specializations: role_specializations(role_name), primary: role_name == primary_role_name)
+    end
   end
 
   def role(name)
@@ -325,6 +327,14 @@ class Kamal::Configuration
       raw_config.servers.is_a?(Array) ? [ "web" ] : raw_config.servers.keys.sort
     end
 
+    def role_specializations(name)
+      if servers.is_a?(Array) || servers[name].is_a?(Array)
+        {}
+      else
+        servers[name].except("hosts")
+      end
+    end
+
     def git_version
       @git_version ||=
         if Kamal::Git.used?

lib/kamal/configuration/role.rb

@@ -2,11 +2,11 @@ class Kamal::Configuration::Role
   CORD_FILE = "cord"
   delegate :argumentize, :optionize, to: Kamal::Utils
 
-  attr_accessor :name
+  attr_reader :name
   alias to_s name
 
-  def initialize(name, config:)
-    @name, @config = name.inquiry, config
+  def initialize(name, config:, specializations:, primary:)
+    @name, @config, @specializations, @primary = name.inquiry, config, specializations, primary
   end
 
   def primary_host
@@ -98,7 +98,7 @@ class Kamal::Configuration::Role
   end
 
   def primary?
-    self == @config.primary_role
+    @primary
   end
 
 
@@ -163,8 +163,14 @@ class Kamal::Configuration::Role
     File.join config.run_directory, "assets", "volumes", container_name(version)
   end
 
+  def previous_roles
+    previous_role_names.map do |role_name|
+      Kamal::Configuration::Role.new(role_name, config: config, specializations: specializations, primary: primary?)
+    end
+  end
+
   private
-    attr_accessor :config
+    attr_reader :config, :specializations
 
     def extract_hosts_from_config
       if config.servers.is_a?(Array)
@@ -207,14 +213,6 @@ class Kamal::Configuration::Role
       end
     end
 
-    def specializations
-      if config.servers.is_a?(Array) || config.servers[name].is_a?(Array)
-        {}
-      else
-        config.servers[name].except("hosts")
-      end
-    end
-
     def specialized_env
       Kamal::Configuration::Env.from_config config: specializations.fetch("env", {})
     end
@@ -237,4 +235,8 @@ class Kamal::Configuration::Role
         options
       end
     end
+
+    def previous_role_names
+      specializations.fetch("previously", [])
+    end
 end