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vercel/errors/now-static-build-failed-to-detect-a-server.md
2020-04-21 19:11:12 -04:00

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# `@now/static-build` Failed to detect a server running
#### Why This Warning Occurred
When running `now dev`, the `@now/static-build` builder proxies relevant HTTP
requests to the server that is created by the `now-dev` script in the
`package.json` file.
In order for `now dev` to know which port the server is running on, the builder
is provided a `$PORT` environment variable that the server _must_ bind to. The
error "Failed to detect a server running on port" is printed if the builder fails
to detect a server listening on that specific port within five minutes.
#### Possible Ways to Fix It
Please ensure that your `now-dev` script binds the spawned development server on
the provided `$PORT` that the builder expects the server to bind to.
For example, if you are using Gatsby, your `now-dev` script must use the `-p`
(port) option to bind to the `$PORT` specified from the builder:
> _In Windows environments, reference the `PORT` environment variable with `%PORT%`_
```
{
...
"scripts": {
...
"now-dev": "gatsby develop -p $PORT"
}
}
```
Consult your static builder program's `--help` or documentation to figure out what
the command line flag to bind to a specific port is (in many cases, it is one of:
`-p` / `-P` / `--port`).