Add a simple validation to the service name to prevent setup issues

lib/kamal/configuration.rb

@@ -218,7 +218,7 @@ class Kamal::Configuration
 
 
   def valid?
-    ensure_destination_if_required && ensure_required_keys_present && ensure_valid_kamal_version
+    ensure_destination_if_required && ensure_required_keys_present && ensure_valid_kamal_version && ensure_valid_service_name
   end
 
   def to_h
@@ -283,6 +283,12 @@ class Kamal::Configuration
       true
     end
 
+    def ensure_valid_service_name
+      raise ArgumentError, "Service name can only include alphanumeric characters and hyphens" unless raw_config[:service] =~ /^[a-z0-9-]+$/
+
+      true
+    end
+
     def ensure_valid_kamal_version
       if minimum_version && Gem::Version.new(minimum_version) > Gem::Version.new(Kamal::VERSION)
         raise ArgumentError, "Current version is #{Kamal::VERSION}, minimum required is #{minimum_version}"

test/configuration_test.rb

@@ -42,6 +42,16 @@ class ConfigurationTest < ActiveSupport::TestCase
     end
   end
 
+  test "service name valid" do
+    assert Kamal::Configuration.new(@deploy.tap { _1[:service] = "hey-app1" }).valid?
+  end
+
+  test "service name invalid" do
+    assert_raise(ArgumentError) do
+      Kamal::Configuration.new @deploy.tap { _1[:service] = "app.com" }
+    end
+  end
+
   test "roles" do
     assert_equal %w[ web ], @config.roles.collect(&:name)
     assert_equal %w[ web workers ], @config_with_roles.roles.collect(&:name)
@@ -299,7 +309,7 @@ class ConfigurationTest < ActiveSupport::TestCase
 
     assert_equal "alternate_web", config.primary_role
     assert_equal "1.1.1.4", config.primary_host
-    assert config.role(:alternate_web).primary? 
+    assert config.role(:alternate_web).primary?
     assert config.role(:alternate_web).running_traefik?
   end