HTTP Load Distribution Using SAP Message Server 

 

SAP recommends that you use the SAP Web Dispatcher as the entrance point for your Web queries. This is then used as the access point for your network and also executes load balancing for HTTP requests.

Uses

Usually, an SAP System consists of several application servers which share the network load.

Load distribution is handled by the message server (there is one message server in an SAP System). When a user logs on, the message server assigns him or her to the application server that currently has the smallest load. This procedure is also used for incoming HTTP requests.

If you are using HTTP load distribution on your system, you cannot use additional Virtual Hosts.

Prerequisites

To distribute load balancing with the SAP Message Server, the following prerequisites must be fulfilled.

·        Parameter ms/http(s)_port must be set (see below).

·        The ICF Services sap/public/icf_info/logon_groups and sap/public/icf_info/urlprefix must be activated (transaction SICF), see Server Groups in Internet Communication Framework.

Process

Every application server that is participating in load sharing tells the message server how many work processes it can provide and whether it accepts HTTPS connections. At the start of a connection, an Internet client first connects to a message server (which must also be HTTP-compatible). The message server tells the client via a redirect which application server it should connect to. Obviously, HTTPS requests are only sent to HTTPS-compatible application servers.

For this procedure to work, the message server has to open one or several additional ports. The following profile parameters are used for this:

·         ms/http_port

This parameter refers to an additional HTTP port that the message server opens to redirect HTTP requests. This parameter refers to an additional HTTP port that the message server opens to redirect HTTP requests.

Default setting: no additional port

Therefore, you must set this parameter if you want to activate HTTP load distribution.

·         ms/https_port

This parameter refers to a HTTPS port that the message server opens to redirect HTTPS requests. This parameter refers to an additional HTTP port that the message server opens to redirect HTTP requests.
Additional SSL parameters must be set for HTTPS, so that SSL can be used. Also, the message server must be run as a multi-threaded program, as every HTTPS request is processed in its own thread.

There are also other parameters with default values that do not need to be changed. These parameters are as follows:

·         ms/http_max_ports:
Maximum number of additional HTTP ports that the message server can open. Default 20.

·         ms/http_max_clients:
Maximum number of HTTP clients that can log on simultaneously to the message server. Default 1000.

·         ms/http_timeout:
Timeout for network operations. If there is no activity on the connection within this time period, the connection to the HTTP client is terminated. The timeout value is expressed in seconds. Default 20.

·         ms/http_bufferln:
Maximum readable length of the HTTP header. This value is expressed in bytes. Default 65636.

If SSL is being used, the SSL parameters must be set correctly (see SSL documentation).