Abstract

This tech note documents the minimal Image Services 4.1.2 software level and the configuration checklist for running Image Services in a cluster environment.

Content

Step A: (Check the minimal Software Level:)

1. Image Services 4.1.2 FP4

2. SCR 350827

Step B: (fn_edit)

Run fn_edit and verify that the cluster name is configured in the Network Name column under the Network tab.

Step C: (Configure cluster address as secondary local address of servers)

IS no longer interrogates the network interface cards for all the local addresses that they support. The code for interrogating network cards was platform dependent, and did not handle IPv6 at all. In order to deal with IPv4 as well as IPv6 in an industry standard way, IS now uses the industry standard getaddrinfo() entry point to resolve network names (i.e., host names and cluster names) to network addresses as follows.

(1) In order to determine the local addresses of the current host, IS calls gethostname() to get the name of the current host. (2) Then IS calls getaddrinfo() passing the local host name to obtain all the local addresses of the current host.

Since IS no longer interrogates the network interface cards directly, it may be the case that IS no longer thinks that the address of the cluster is a secondary address of either cluster server. If that is the case, then the problem must be corrected by modifying the host files and/or the name server database to add the cluster address as a secondary local address of each of the two servers. (The cluster address must be a secondary address so that the legacy entry point gethostbyname() returns the same IPv4 address for the server after the modification as it did before the modification.)

On most systems, to resolve a name to its network addresses, getaddrinfo() first attempts to find the name in a name server database. If it succeeds in doing so, it uses the addresses in the name server database and does not look at the local hosts file. If there is no name server or the name database does not contain the name, getaddrinfo() uses the local host file.

On some platforms it is possible to configure the OS to change the search order to use the local host file first, then the name server. On Some platforms, it is impossible to affect the search order of getaddrinfo(). That can be confusing, because it is not what you are used to, so you might not understand why all the changes you make to the hosts files to get the system to come up have no effect.

The recommended search order is first name server, then local host file. That gives the network administrator as much control as he wants to exercise over name resolution.

Step C-a: (modifying the host file)

The existing hosts file should already have a line that looks similar to the following:

<Cluster IP_address> <Cluster name> <four_part_NCH_service_name>

Append the server's host name to the end of the above line as follows.

<Cluster IP_address> <Cluster name> <four_part_NCH_service_name> <hostname>

That makes the cluster address a secondary local address of the server, assuming the line with the server address occurred first in the host file. The line for the host address would look like:

<IP_address_of_host> <host name>


For example for IS domain “titan:yourco”:

The hosts file on server 1 (i.e., titan1) might look like the following:

9.42.31.99 titan1
9.42.31.3 TitanCluster titan-yourco-nch-server

After the change, it would look like the following:

9.42.31.99 titan1
9.42.31.3 TitanCluster titan-yourco-nch-server titian1

The hosts file on server 2 (i.e., titan2) might look like the following:

9.42.31.88 titan2
9.42.31.3 TitanCluster titan-yourco-nch-server

After the change, it would look like the following:

9.42.31.88 titan2
9.42.31.3 TitanCluster titian-yourco-nch-server titian2

Note that the two server addresses and the cluster address are all different from each other. Note also that the server names and the cluster name are all different from each other.


Step C-b: (Configure Name Server)

If a name server is used for name/address resolution, the entry in hosts file in Step C will be ignored (assuming the name server is searched first). In that case, the cluster address must be added to the DNS server as the secondary address for each of the two host servers.

For example, “nslookup ibm.com” resolves “ibm.com” to one primary address and two secondary addresses.

Name: ibm.com
Addresses: 129.42.18.103, 129.42.16.103, 129.42.17.103

Your name server should resolve the local fixed IP address as the primary address and the cluster IP address as secondary address for the host server.


Step D: (fn_build -a)

Run fn_build -a

Step E: (fn_setup)

Run fn_setup

Related information

Image Services HA Procedures and Guidelines