How do root and alias map URLs to files in Nginx?

Question

IT Interview Practice · Accepted Answer

Use `root` to append the URL path to a directory. Use `alias` to replace a matching URL prefix with a directory.

## Send the same request to two alternatives

For a request to `/images/logo.png`, compare these alternative locations inside a server block; install only one at a time:

```nginx
location /images/ {
    root /srv/site;
}
```

This looks for `/srv/site/images/logo.png`: the full path `/images/logo.png` is appended to `/srv/site`.

```nginx
location /images/ {
    alias /srv/assets/;
}
```

This looks for `/srv/assets/logo.png`: `/images/` is replaced by `/srv/assets/`.

## Which should you choose?

Choose `root` when the URL mirrors your folder structure. Choose `alias` when the public URL and the real folder have different names. If the result is 404, calculate the final path and check that the worker can read it before changing unrelated settings.

Keep slash boundaries consistent. These examples use prefix locations; an alias in a regular-expression location needs its own path/capture handling.

[Official documentation](https://nginx.org/en/docs/http/ngx_http_core_module.html#alias).

Send the same request to two alternatives

Related questions

Which should you choose?