Add Kamal by default to Rails 8 (rails#51798)

* Add Kamal by default

Author: dhh

railties/CHANGELOG.md

@@ -1,2 +1,6 @@
+*   Use Kamal for deployment by default, which includes generating a Rails-specific config/deploy.yml.
+    This can be skipped using --skip-kamal. See more: https://kamal-deploy.org/
+
+    *DHH* 
 
 Please check [7-2-stable](https://github.com/rails/rails/blob/7-2-stable/railties/CHANGELOG.md) for previous changes.

railties/lib/rails/generators/app_base.rb

@@ -112,6 +112,9 @@ def self.add_shared_options_for(name)
         class_option :skip_devcontainer,   type: :boolean, default: false,
                                            desc: "Skip devcontainer files"
 
+        class_option :skip_kamal,          type: :boolean, default: false,
+                                           desc: "Skip Kamal setup"
+
         class_option :dev,                 type: :boolean, default: nil,
                                            desc: "Set up the #{name} with Gemfile pointing to your Rails checkout"
 
@@ -407,6 +410,10 @@ def skip_devcontainer?
         options[:skip_devcontainer]
       end
 
+      def skip_kamal?
+        options[:skip_kamal]
+      end
+
       class GemfileEntry < Struct.new(:name, :version, :comment, :options, :commented_out)
         def initialize(name, version, comment, options = {}, commented_out = false)
           super
@@ -718,6 +725,16 @@ def run_css
         end
       end
 
+      def run_kamal
+        return if options[:skip_kamal] || !bundle_install?
+
+        bundle_command "binstubs kamal"
+        bundle_command "exec kamal init"
+
+        template "env.erb", ".env.erb"
+        template "config/deploy.yml", force: true
+      end
+
       def add_bundler_platforms
         if bundle_install?
           # The vast majority of Rails apps will be deployed on `x86_64-linux`.

railties/lib/rails/generators/rails/app/app_generator.rb

@@ -570,6 +570,7 @@ def finish_template
       public_task :run_javascript
       public_task :run_hotwire
       public_task :run_css
+      public_task :run_kamal
 
       def run_after_bundle_callbacks
         @after_bundle_callbacks.each(&:call)

railties/lib/rails/generators/rails/app/templates/Gemfile.tt

@@ -19,6 +19,11 @@ gem "tzinfo-data", platforms: %i[ <%= bundler_windows_platforms %> jruby ]
 # Reduces boot times through caching; required in config/boot.rb
 gem "bootsnap", require: false
 <% end -%>
+<% unless options.skip_kamal? -%>
+
+# Deploy this application anywhere as a Docker container [https://kamal-deploy.org]
+gem "kamal", require: false
+<% end -%>
 <% unless skip_active_storage? -%>
 
 # Use Active Storage variants [https://guides.rubyonrails.org/active_storage_overview.html#transforming-images]

railties/lib/rails/generators/rails/app/templates/config/databases/sqlite3.yml.tt

@@ -21,6 +21,7 @@ test:
   database: storage/test.sqlite3
 
 
+<%- if options.skip_kamal? -%>
 # SQLite3 write its data on the local filesystem, as such it requires
 # persistent disks. If you are deploying to a managed service, you should
 # make sure it provides disk persistence, as many don't.
@@ -30,3 +31,10 @@ test:
 production:
   <<: *default
   # database: path/to/persistent/storage/production.sqlite3
+<%- else -%>
+# Store production database in the storage/ directory, which by default
+# is mounted as a persistent Docker volume in config/deploy.yml.
+production:
+  <<: *default
+  database: storage/production.sqlite3
+<%- end -%>

railties/lib/rails/generators/rails/app/templates/config/deploy.yml.tt

@@ -0,0 +1,85 @@
+# Name of your application. Used to uniquely configure containers.
+service: <%= app_name %>
+
+# Name of the container image.
+image: your-user/<%= app_name %>
+
+# Deploy to these servers.
+servers:
+  web:
+    - 192.168.0.1
+  # job:
+  #   hosts:
+  #     - 192.168.0.1
+  #   cmd: bin/solid_queue work
+
+# Credentials for your image host.
+registry:
+  # Specify the registry server, if you're not using Docker Hub
+  # server: registry.digitalocean.com / ghcr.io / ...
+  username: your-user
+
+  # Always use an access token rather than real password when possible.
+  password:
+    - KAMAL_REGISTRY_PASSWORD
+
+# Inject ENV variables into containers (secrets come from .env).
+# Remember to run `kamal env push` after making changes!
+env:
+  secret:
+    - RAILS_MASTER_KEY
+  # clear:
+  #   DB_HOST: 192.168.0.2
+
+# Use a persistent storage volume for sqlite database files and local Active Storage files.
+# Recommended to change this to a mounted volume path that is backed up off server.
+volumes:
+  - "<%= app_name %>_storage:/rails/storage"
+
+# Bridge fingerprinted assets, like JS and CSS, between versions to avoid
+# hitting 404 on in-flight requests. Combines all files from new and old
+# version inside the asset_path.
+asset_path: /rails/public/assets
+
+# Use a different ssh user than root
+# ssh:
+#   user: app
+
+# Configure builder setup (defaults to multi-arch images).
+# builder:
+#   # Build same-arch image locally (use for x86->x86)
+#   multiarch: false
+#
+#   # Build diff-arch image via remote server
+#   remote:
+#     arch: amd64
+#     host: ssh://[email protected]
+#
+#   args:
+#     RUBY_VERSION: <%= ENV["RBENV_VERSION"] || ENV["rvm_ruby_string"] || "#{RUBY_ENGINE}-#{RUBY_ENGINE_VERSION}" %>
+#   secrets:
+#     - GITHUB_TOKEN
+#     - RAILS_MASTER_KEY
+
+# Use accessory services (secrets come from .env).
+# accessories:
+#   db:
+#     image: mysql:8.0
+#     host: 192.168.0.2
+#     port: 3306
+#     env:
+#       clear:
+#         MYSQL_ROOT_HOST: '%'
+#       secret:
+#         - MYSQL_ROOT_PASSWORD
+#     files:
+#       - config/mysql/production.cnf:/etc/mysql/my.cnf
+#       - db/production.sql:/docker-entrypoint-initdb.d/setup.sql
+#     directories:
+#       - data:/var/lib/mysql
+#   redis:
+#     image: redis:7.0
+#     host: 192.168.0.2
+#     port: 6379
+#     directories:
+#       - data:/data

railties/lib/rails/generators/rails/app/templates/env.erb.tt

@@ -0,0 +1,5 @@
+<%%# This env template should lookup values from a password store or from ENV -%>
+# Generated by kamal envify from .env.erb
+KAMAL_REGISTRY_PASSWORD=<%%= ENV["KAMAL_REGISTRY_PASSWORD"] %>
+RAILS_MASTER_KEY=<%%= File.read("config/master.key") %>
+# GITHUB_TOKEN=<%%#= `gh config get -h github.com oauth_token`.strip %>

railties/lib/rails/generators/rails/plugin/plugin_generator.rb

@@ -115,6 +115,7 @@ def generate_test_dummy(force = false)
       opts[:skip_brakeman] = true
       opts[:skip_bundle] = true
       opts[:skip_ci] = true
+      opts[:skip_kamal] = true
       opts[:skip_git] = true
       opts[:skip_hotwire] = true
       opts[:skip_rubocop] = true

railties/test/generators/app_generator_test.rb

@@ -654,6 +654,20 @@ def test_ci_files_are_skipped_if_required
     assert_no_file ".github/dependabot.yml"
   end
 
+  def test_inclusion_of_kamal_files
+    run_generator_and_bundler [destination_root]
+
+    assert_file "config/deploy.yml"
+    assert_file ".env.erb"
+  end
+
+  def test_kamal_files_are_skipped_if_required
+    run_generator_and_bundler [destination_root, "--skip-kamal"]
+
+    assert_no_file "config/deploy.yml"
+    assert_no_file ".env.erb"
+  end
+
   def test_usage_read_from_file
     assert_called(File, :read, returns: "USAGE FROM FILE") do
       assert_equal "USAGE FROM FILE", Rails::Generators::AppGenerator.desc