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Chapter 8: Planning for HACMP Clients


This chapter discusses planning considerations for HACMP clients. This is the last step before proceeding to installation of your HACMP software. This chapter contains the following sections:

  • Prerequisites
  • Overview
  • Clients Running Clinfo
  • Clients Not Running Clinfo
  • Network Components
  • Where You Go from Here.
  • Prerequisites

    By now, you should have completed the planning steps in the previous chapters:

  • Chapter 2: Initial Cluster Planning
  • Chapter 3: Planning Cluster Network Connectivity
  • Chapter 4: Planning Shared Disk and Tape Devices
  • Chapter 5: Planning Shared LVM Components
  • Chapter 6: Planning Resource Groups
  • Chapter 7: Planning for Cluster Events.
  • Overview

    HACMP clients are end-user devices that can access the nodes in an HACMP cluster. In this step of the planning process, you evaluate the cluster from the point of view of the clients.

    HACMP clients may contain hardware and software from a variety of vendors. To maintain connectivity to the HACMP cluster, consider the issues in the following sections.

    Client Application Systems

    All clients should run Clinfo if possible. If you have hardware other than IBM eServer pSeries nodes in the configuration, you may want to port Clinfo to those platforms. Clinfo source code is provided as part of HACMP.

    You need to think about what applications are running on these clients. Who are the users? Is it required or appropriate for users to receive a message when cluster events affect their system?

    NFS Servers

    For information about NFS-related issues, see the section Using NFS with HACMP in Chapter 5: Planning Shared LVM Components.

    Terminal Servers

    If you plan to use a terminal server on the local area network, consider the following when choosing the hardware:

  • Can you update the terminal server’s ARP cache? The terminal server must comply with the TCP/IP protocol, including Telnet.
  • Is the terminal server programmable, or does it need manual intervention when a cluster event happens?
  • Can you download a control file from the cluster node to the terminal server that updates or handles cluster events’ effects on clients?
  • If your terminal server does not meet these operating requirements, choose the hardware address swapping option when configuring the cluster environment.

    Clients Running Clinfo

    The Clinfo program calls the /usr/es/sbin/cluster/etc/clinfo.rc script whenever a network or node event occurs. By default, this action updates the system’s ARP cache to reflect changes to network addresses. You can customize this script if further action is desired.

    Reconnecting to the Cluster

    Clients running the Clinfo daemon will be able to reconnect to the cluster quickly after a cluster event. If you have hardware other than IBM eServer pSeries between the cluster and the clients, make sure that you can update the ARP cache of those network components after a cluster event occurs.

    If you configure the cluster to swap hardware addresses as well as IP addresses, you do not need to be concerned about updating the ARP cache. However, be aware that this option causes a longer delay for the users.

    If you are using IPAT via IP Aliases, make sure all your clients support TCP/IP gratuitous ARP.

    Customizing the clinfo.rc Script

    For clients running Clinfo, decide whether to customize the /usr/es/sbin/cluster/etc/clinfo.rc script to do more than update the ARP cache when a cluster event occurs. For more information, see the chapter on Installing HACMP on Client Nodes in the Installation Guide. Also see the Programming Client Applications guide for a sample clinfo.rc script.

    Clients Not Running Clinfo

    On clients not running Clinfo, you may have to update the local ARP cache indirectly by pinging the client from the cluster node. On the cluster nodes, add the name or address of a client host you want to notify to the PING_CLIENT_LIST variable in the clinfo.rc script. When a cluster event occurs, clinfo.rc runs the following command for each host specified in PING_CLIENT_LIST:

    ping -c1 $host 
    

    This assumes the client is connected directly to one of the cluster networks.

    Network Components

    If you configured the network so that clients attach to networks on the other side of a router, bridge, or gateway rather than to the cluster’s local networks, be sure that you can update the ARP cache of those network components after a cluster event occurs. If this is not possible, then make sure to use hardware address swapping when you configure the cluster environment.

    Where You Go from Here

    This chapter concludes the planning process. You can now begin to install the HACMP software. For detailed instructions, see the Installation Guide.


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