GuidesLanguage guides

Three rules for every language

The port, the start command and the build command obey the same rules in every language.

The build command runs after the install of the dependencies.

1 / 3

Listen on `0.0.0.0` and on `PORT`

Ferry sets PORT to the port that it routes to. The value is 10000, unless one of these is true:

You set --port.
You set a PORT variable.
Your image exposes one port only.

See The port of your app.

The start command

Ferry uses the first start command that exists:

The start command of the service (--start-cmd).
The entry of the Procfile for the type of the service.
The default of the language.

Type of service	Procfile entry
Web service, private service	`web:`
Background worker	`worker:`
Cron job	`cron:`, then `worker:`

The build command

A build command (--build-cmd) runs after the install of the dependencies. It can read your environment variables.

The files Ferry looks for

Ferry chooses the runtime from the first known file at the root of your source.

Node.js

Ferry builds a Node.js app from package.json, with npm, Yarn, pnpm or Bun.

On this page

Listen on 0.0.0.0 and on PORTThe start command The build command