Server Groups in the Internet Communication Framework 

In the ICF (Internet Communication Framework, Transaction SICF) within the SAP NetWeaver Application Server, all virtual host names  that can be handled by the SAP NW AS (see also Virtual Hosts) are configured. Every virtual host name has a unique prefix with which the URL begins.

You can find some services in the HTTP service tree (Transaction SICF) that provide information about URL prefixes and logon groups. You can find these services in the tree under sap/public/icf_info.

• If you use HTTP Load Balancing Using the SAP Message Server, /urlprefix outputs the list of URL prefixes that are handled in the AS ABAP. This is how the message server finds out which URLs must be forwarded where.
• /icr_urlprefix returns the same information, but for the SAP Web dispatcher, if this is used for load balancing.

Since there can be no redirects when the SAP Web dispatcher is used, SAP recommends this method.

•  /logon_groups specifies a list of URL prefixes for which a logon group is defined (in Transaction SICF). The requests are only forwarded to the server that is defined in this logon group. This is how a load distribution mechanism is implemented, based on URLs.
• /icr_groups outputs all servers (host names) and logon groups that you have maintained in this system (Transaction SMLG).

The SAP Web dispatcher fetches this list from an application server. It can use this list to:

·        Decide whether it is an ABAP or a J2EE request

·        Carry out load balancing for the servers in question.

The procedure for this is described in detail in Server Selection and Load Balancing Using the SAP Web Dispatcher.

Relevant Profile Parameters

The following parameters are described in Profile Parameters of the SAP Web Dispatcher.

·        is/HTTP/default_root_hdldetermines which root directory is to be used – either the root directory of the ICF (ABAP) or of the J2EE server. Permitted values are abap and j2ee.

·        wdisp/max_server_groups specifies the maximum number of logon group entries that can be  managed in the message server. The default is 128.

·        wdisp/max_server_group_name_lenspecifies the maximum length of a logon group entry; the default is 20.

·        wdisp/max_url_map_entries is the maximum length of the prefix entries that can be managed in the SAP Web dispatcher; the default is 300.

·        wdisp/max_url_map_path_lenspecifies the maximum path length of the URL mapping table of the SAP Web dispatcher. The default is 256.

·        wdisp/url_map_location The path in the HTTP service tree (Transaction SICF), under which the URL mapping information for the SAP Web dispatcher is stored. The default is /sap/public/icf_info/icr/urlprefix.