choosing backend based on header value

[Alexandr Gomoliako]

> This is exactly what I thought. But then is there a way without
> explicitly specifying the nodes.?
> I understand the pitfalls, its just to be used for testing purposes.
> (like sending a request to a test server)

There is:

map $http_x_caching_node $x {
    default  backend_boxes;
    ~.  $http_x_caching_node;
}