puma--puma/docs/plugins.md

## Plugins

Puma 3.0 added support for plugins that can augment configuration and service
operations.

2 canonical plugins to look to aid in development of further plugins:

* [tmp\_restart](https://github.com/puma/puma/blob/master/lib/puma/plugin/tmp_restart.rb):
  Restarts the server if the file `tmp/restart.txt` is touched
* [heroku](https://github.com/puma/puma-heroku/blob/master/lib/puma/plugin/heroku.rb):
  Packages up the default configuration used by puma on Heroku (being sunset with the release of Puma 5.0)

Plugins are activated in a puma configuration file (such as `config/puma.rb'`)
by adding `plugin "name"`, such as `plugin "heroku"`.

Plugins are activated based simply on path requirements so, activating the
`heroku` plugin will simply be doing `require "puma/plugin/heroku"`. This
allows gems to provide multiple plugins (as well as unrelated gems to provide
puma plugins).

The `tmp_restart` plugin is bundled with puma, so it can always be used.

To use the `heroku` plugin, add `puma-heroku` to your Gemfile or install it.

### API

## Server-wide hooks

Plugins can use a couple of hooks at server level: `start` and `config`.

`start` runs when the server has started and allows the plugin to start other
functionality to augment puma.

`config` runs when the server is being configured and is passed a `Puma::DSL`
object that can be used to add additional configuration.

Any public methods in [`Puma::Plugin`](../lib/puma/plugin.rb) are the public API that any plugin may
use.