Application Server List 

In order to perform load balancing, the SAP Web Dispatcher periodically fetches a list of all active application servers of an SAP system. This list includes the host names as well as a static value indicating the capacity of each server. Currently the capacity value is simply the number of dialog processes of the corresponding server.

Servers will be dynamically added and removed from the list whenever the SAP Message Server detects a new server starting up or a running server shutting down (or crashing), respectively. However, since the list will normally only be updated after a certain time interval (e.g. several minutes), it is recommended that a load-balancing device remove crashed servers from the list immediately.

The application server list is fetched via HTTP from the SAP Message Server, which is the one central component of each SAP System that routes internal messages among application servers and is thus informed about the current status of each server.

The URL to retrieve the list is determined by the SAP configuration parameter wdisp/server_info_location that by default is /msgserver/text/logon.

The network host name and HTTP port of the SAP Message Server is configured via SAP configuration parameters rdisp/mshost and ms/http_port, respectively.

For simplicity and performance, a plain text format is used in the HTTP message body to describe the server list as a set of server description records (separated by empty lines) as follows ( CRLFdenotes the Control/LineFeed as end-of-line indicator):

<server-list> =                                                   

      "version"<major> "."<minor> CRLF                             

      <sap-server-name> CRLF                                        

      <protocol-type> <host> <port> <description> CRLF            

      ...                                                          

      <protocol-type> <host> <port> <description> CRLF              

      CRLF                                                         

      <sap-server-name> CRLF                                       

      <protocol-type> <host> <port> <description> CRLF             

      ...                                                          

      <protocol-type> <host> <port> <description> CRLF

 

<description> = <process type> “=”<n>

<process type> = [ “DIA“ | … ]

            

Example

version 1.0

P58864_BIN_53

DIAG P58864   3253  DIA=3

RFC  P58864   3353 

HTTP P58864   2727 

 

P58056_BIN_53

DIAG P58056   3253  DIA=2

RFC  P58056   3353 

 

ls3022_BIN_14

DIAG ls3022   3214  DIA=2

DIAGS   ls3022   3214  p:CN=BIN, O=SAP-AG, C=DE

RFC  ls3022   3314 

RFCS ls3022   4814  p:CN=BIN, O=SAP-AG, C=DE

HTTP ls3022   2525 

HTTPS   ls3022   2626 

In this example there are two servers supporting the HTTP protocol, namely P58864_BIN_53 (capacity: 3 dialog processes) and  ls3022_BIN_14 (capacity: 2 dialog processes), respectively.[GQM1]