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. The capacity value is simply the number of dialog processes of the corresponding server. This applies for servers which contain AS ABAP. For AS Java servers (without AS ABAP) the capacity is the number of Java server processes.

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“ | … ]

            

Examples

version 1.0

WDFD00146299A_Y7A_77

DIAG  WDFD00146299A.wdf.sap.corp 3277  LB=3

RFC   WDFD00146299A.wdf.sap.corp 3377 

HTTP  WDFD00146299A.wdf.sap.corp 50077

SMTP  WDFD00146299A.wdf.sap.corp 8025 

 

us4293_Y7A_77

DIAG  us4293.wdf.sap.corp  3277  LB=16

DIAGS us4293.wdf.sap.corp  3277  p/secude:CN=Y7A, O=SAP-AG, C=DE

RFC   us4293.wdf.sap.corp  3377 

RFCS  us4293.wdf.sap.corp  4877  p/secude:CN=Y7A, O=SAP-AG, C=DE

HTTP  us4293.wdf.sap.corp  50077

SMTP  us4293.wdf.sap.corp  25077

 

us4297_Y7A_77

DIAG  us4297.wdf.sap.corp  3277  LB=12

DIAGS us4297.wdf.sap.corp  3277  p/secude:CN=Y7A, O=SAP-AG, C=DE

RFC   us4297.wdf.sap.corp  3377 

RFCS  us4297.wdf.sap.corp  4877  p/secude:CN=Y7A, O=SAP-AG, C=DE

HTTP  us4297.wdf.sap.corp  50077

HTTPS us4297.wdf.sap.corp  44377

SMTP  us4297.wdf.sap.corp  25077

J2EE  us4297.wdf.sap.corp  57700 LB=1

J2EES us4297.wdf.sap.corp  57701 LB=1

 

In this example there are two servers containing AS ABAP only, namely WDFD00146299A_Y7A_77 (capacity (number of dialog processes): 3) and  us4293_Y7A_77 (capacity: 16). One instance (us4297_Y7A_77) contains AS ABAP and AS Java. AS ABAP capacity is 12, AS Java capacity is 1, the overall capacity of the server is the maximum of the two values (default behavior which you can change in the web admin interface of the Web Dispatcher or by profile parameters.

 

More Information

Capacity of an Application Server

Using the Web Administration Interface