Merge branch 'main' into valid_service_name

lib/kamal/configuration.rb

@@ -127,6 +127,10 @@ class Kamal::Configuration
     raw_config.require_destination
   end
 
+  def retain_containers
+    raw_config.retain_containers || 5
+  end
+
 
   def volume_args
     if raw_config.volumes.present?
@@ -218,7 +222,7 @@ class Kamal::Configuration
 
 
   def valid?
-    ensure_destination_if_required && ensure_required_keys_present && ensure_valid_kamal_version && ensure_valid_service_name
+    ensure_destination_if_required && ensure_required_keys_present && ensure_valid_kamal_version && ensure_retain_containers_valid && ensure_valid_service_name
   end
 
   def to_h
@@ -297,6 +301,12 @@ class Kamal::Configuration
       true
     end
 
+    def ensure_retain_containers_valid
+      raise ArgumentError, "Must retain at least 1 container" if retain_containers < 1
+
+      true
+    end
+
 
     def role_names
       raw_config.servers.is_a?(Array) ? [ "web" ] : raw_config.servers.keys.sort