Communications Server

Network Administration Guide


Chapter 11. Planning for Load Balancing

This chapter gives an overview of planning for load balancing. It describes planning for dependent LU and LU 6.2 load balancing.


Dependent LU Load Balancing

Load balancing allows you to balance dependent host sessions across servers. Load balancing is supported for LUx API applications through SNA API clients, 3270 emulators, and TN3270 emulators.

When Communications Server responds to client requests, it sorts servers supporting the requested pool by load.

The load for dependent LUs represents a percentage of available resources from a particular server. The load percentage is calculated by dividing the number of active application connections by the total number of LUs (0 to 3) available.

You can influence the calculated load by specifying an LU0- to-3 load factor (host session load factor) to compensate for differences between two servers, such as available memory, processor speed, and CPU utilization. You can also use the LU0-to-3 load factor to balance the loads between Communications Servers and Novell NetWare for SAA servers.

Notes:

  1. The servers participating in load balancing are determined by LU pool membership and by scope membership. All Communications Servers with LUs in pools of the same name are subject to load balancing.

  2. Clients using TCP/IP protocol can participate in load balancing. However, TCP/IP clients can load balance only between IBM Communications Servers. Load balancing is determined by configured scopes.

In Communications Server, if LU pools on different servers have the same name, they function as one pool for load balancing. When assigning LUs to an LU pool, select from the host links on a server, and assign LUs from the selected host link to the LU pool. These LUs do not need to be of the same LU type. Also, the resulting pool can contain LUs from multiple links.


LU 6.2 Load Balancing

Load balancing allows you to balance independent LU 6.2 sessions by distributing them across multiple servers. Load balancing is supported for APPC API applications through SNA API clients and TN5250 emulators.

The load for LU6.2 represents a percentage of available resources from a particular server. The load percentage is calulated by dividing the total number of conversations over all local LUs on a particular server by the cumulative maximum session limit for all local LUs. The maximum session limit is the LU 6.2 session limit specified during configuration. If the maximum session limit is specified as zero (0), indicating there is no session limit, the default maximum local LU session limit of 512 per local LU is used when the load is calculated. The default maximum local LU session limit can also be specified during configuration.

You can influence the calculated load by specifying an LU6.2 load factor (APPC session load factor) to compensate for differences between two servers, such as available memory, processor speed, and CPU utilization. You can also use the LU6.2 load factor to balance the loads between Communications Servers and Novell NetWare for SAA servers.
Note:Clients using TCP/IP protocol can participate in LU 6.2 load balancing.


Planning for TCP/IP Scopes

Scope is a parameter used to control and manage access by TCP/IP clients to servers in a network. It is the same as the service location protocol (SLP) scope as referenced in RFC 2165. The SLP is used by Communications Server to implement TCP/IP-based load balancing.

The control scope provided is necessary for two reasons:

The meaning of the scope values are defined by the administrator of the network. These values can represent any entity. Commonly, they fall along either departmental, geographical, or organizational lines.

Once configured, clients are able to reach the SNA network through servers that are configured with the same scope or that have no associated scope (unscoped services or servers).
Note:If a server is configured as unscoped, it replies to SLP scoped and unscoped requests. If the SNA API client is configured to connect to unscoped servers, only unscoped servers will reply.

Scopes and Client Server Security

Communications Server enables Novell NetWare for SAA clients to use Windows NT domain security to authenticate the client connection to the server without reentering the userid and password. The client must be part of a Windows NT domain, either by participation in a Communications Server domain or logging in locally with a synchronized userid and password.

The authorized users for client server are maintained in the IBMCSAPI local group, which is located either directly on the Communications Server or on the domain controller where Communications Server participates. This user group is created during installation and can be administered using the Windows NT User Manager application.

Novell NetWare for SAA client users outside of the Windows NT domain must replicate the userid and password across all servers configured with the same scope.

Where Scope is Configured

Each server is assigned to a scope or scopes through SNA Node Configuration. Clients using these servers must be configured to connect to servers within a single specific scope or to unscoped servers. For more information on configuring clients, refer to Client/Server Communications Programming.

How Scope Relates to SLP

Communications Server scope relates directly to service location protocol (SLP) scope. Therefore, SLP directory agents may reside in the network that support the Communications Server configured scopes. If you plan to allow clients to locate Communications Server services based on scopes, consider how scope relates to the network as a whole. If there are unscoped services in a network where scopes are also used, the unscoped services are eligible to satisfy any scoped requests, which can potentially put a burden on those service agents and directory agents that support the unscoped services.
Note:If the SNA API client is configured to connect to unscoped servers, only unscoped servers will reply.

If directory agents are to be used in the site network (for upward scaling), they should be configured to handle the same scopes as are configured for the Communications Server. In addition, if unscoped services are to be used in networks with directory agents, at least one unscoped directory agent should be configured.

Communications Server includes an SLP service agent that is installed on every server where Communications Server is installed. No additional SLP support needs to be installed in the network in order for TCP/IP load balancing and Communications Server discovery to work properly.


Tracking the Current Load

You can track the current load for both LU 6.2 and dependent LUs using the Windows NT Performance Monitor. You can start the performance monitor from the Administrative Tools (Common) selection of the Programs menu.

From the performance monitor screen, select Add to Chart from the Edit pulldown. In the Object field, select IBM SNA Load Balancing. The two counters listed are:

LU0/LU3 Load
Use this counter to track the load for dependent LUs.

LU6.2 Load
Use this counter to track the load for LU 6.2 LUs.

The results of the load tracking can be saved for future reference.


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