Capistrano::Cable

Capistrano::Cable helps to deploy standalone ActionCable server with Puma over systemd. It doesn't use a specific puma.rb for Puma configuration, it relies on given options.

Installation

Install the gem and add to the application's Gemfile by executing:

$ bundle add capistrano-cable

If bundler is not being used to manage dependencies, install the gem by executing:

$ gem install capistrano-cable

Usage

# Capfile

require 'capistrano/cable'
install_plugin Capistrano::Cable::Systemd

To prevent loading the hooks of the plugin, add false to the load_hooks param.

# Capfile

install_plugin Capistrano::Cable, load_hooks: false  # Default cable tasks without hooks

To make it work with rvm, rbenv and chruby, install the plugin after corresponding library inclusion.

# Capfile

require 'capistrano/rbenv'
require 'capistrano/cable'
install_plugin Capistrano::Cable

Config

Many options are available to customize the cable server configuration. Here are the main ones:

# config/deploy.rb or config/deploy/<stage>.rb
set :cable_role, :web
set :cable_bind, -> { "unix://#{shared_path.join("tmp", "sockets", "cable.sock")}" }
# set :cable_limit_nofile, 65536 # optional, to customize if `Errno::EMFILE: Too many open files` happens
set :cable_rackup_file, 'cable/config.ru'
set :cable_dir, -> { File.join(release_path, "cable") }
set :cable_pidfile, -> { File.join(shared_path, "tmp", "pids", "cable.pid") }
set :cable_env, -> { fetch(:rack_env, fetch(:rails_env, fetch(:stage))) }
set :cable_access_log, -> { File.join(shared_path, "log", "cable.access.log") }
set :cable_error_log, -> { File.join(shared_path, "log", "cable.error.log") }
set :cable_phased_restart, -> { true }
set :cable_enable_socket_service, true
set :cable_service_unit_env_files, -> { fetch(:service_unit_env_files, []) }
set :cable_service_unit_env_vars, -> { fetch(:service_unit_env_vars, []) }
set :cable_service_templates_path, fetch(:service_templates_path, "config/deploy/templates")

See Capistrao::Cable::Systemd#set_defaults for more details.

Where the server listens

cable_bind is the only option about listening. It takes a Puma bind string, or an array of them:

set :cable_bind, "unix:///home/myapp/public_html/shared/tmp/sockets/cable.sock"
set :cable_bind, "tcp://0.0.0.0:28090"
set :cable_bind, "ssl://0.0.0.0:28090?cert=/path/cert.pem&key=/path/key.pem"

By default the server listens on a unix socket in the shared directory, which keeps it unreachable from the outside and saves picking a free port on every host. The socket directory is created by cable:install; the web server in front then proxies to that socket path instead of a host and port, the way it proxies to any other unix socket.

A unix socket path has to be absolute: write unix:///path/to/cable.sock, with three slashes.

Socket activation

With cable_enable_socket_service (enabled by default), systemd owns the listening socket and hands it over to Puma. The socket stays open while the service restarts, so connections are queued in the backlog instead of being refused, and the server is started on the first request if it is not running yet.

The ListenStream of the socket unit is the address of each cable_bind: Puma matches the socket it receives against its own binds, so both are always written from the same option.

Migrating to 0.2.0

cable_port, cable_ssl_certificate and cable_ssl_certificate_key are gone, replaced by cable_bind. A deploy that still sets one of them stops on deploy:starting, before anything is uploaded, with a message telling what to write instead. cable:install refuses to run too, for setups that install the plugin without its hooks.

Nothing else to do on the Capistrano side: the systemd units are now installed at every deploy, before the server is restarted, so upgrading the gem and deploying is enough to move an app to its socket.

The one manual step is the web server, which has to proxy to the socket instead of the port. If both can't be changed in the same window, keep the port for now:

set :cable_bind, "tcp://0.0.0.0:28090"

and move to the default socket in a later deploy.

Development

After checking out the repo, run bin/setup to install dependencies. Then, run rake test to run the tests. You can also run bin/console for an interactive prompt that will allow you to experiment.

To install this gem onto your local machine, run bundle exec rake install. To release a new version, update the version number in version.rb, and then run bundle exec rake release, which will create a git tag for the version, push git commits and the created tag, and push the .gem file to rubygems.org.

Contributing

Bug reports and pull requests are welcome on GitHub at https://github.com/codeur/capistrano-cable. This project is intended to be a safe, welcoming space for collaboration, and contributors are expected to adhere to the code of conduct.

Largely inspired from capistrano-puma gem.

License

The gem is available as open source under the terms of the MIT License.

Code of Conduct

Everyone interacting in the Capistrano::Cable project's codebases, issue trackers, chat rooms and mailing lists is expected to follow the code of conduct.