This GitBook plugin can redirect gitbook page.

Add to your book.json plugin list:

{
    "plugins" : [ "redirect-sub@https://github.com/nats-io/gitbook-plugin-redirect-sub.git" ],
    "pluginsConfig": {
        "redirect_sub" : {
            "root" : "your-redirect-url-root",
            "bookname" : "your-book-name"
        }
    }
}

For example, when you write below config in book.json,

"redirect_sub" : {
    "root" : "https://books.example.com",
}

and you access to https://example.gitbook.io/xxx/yyy.html , you will be redirected to https://books.example.com/xxx/yyy.html.

This plugin reuses many codes of gitbook-plugin-redirect Plugin. Many thanks to ketan.