.. _config_http_filters_on_demand: On-demand VHDS and S/RDS Updates ================================ The on demand filter can be used to support either on demand VHDS or S/RDS update if configured in the filter chain. The on-demand update filter can be used to request a :ref:`virtual host ` data if it's not already present in the :ref:`Route Configuration `. The contents of the *Host* or *:authority* header is used to create the on-demand request. For an on-demand request to be created, :ref:`VHDS ` must be enabled and either *Host* or *:authority* header be present. The on-demand update filter can also be used to request a *Route Configuration* data if RouteConfiguration is specified to be loaded on demand in the :ref:`Scoped RouteConfiguration `. The contents of the HTTP header is used to find the scope and create the on-demand request. On-demand VHDS and on-demand S/RDS can not be used at the same time at this point. Configuration ------------- * :ref:`v3 API reference ` * This filter should be configured with the name *envoy.filters.http.on_demand*. * The filter should be placed before *envoy.filters.http.router* filter in the HttpConnectionManager's filter chain.