In larger networks, especially networks that extend across a wide area network (WAN) it is often desirable to run User Name Mapping on multiple computers. In the case of a WAN, running User Name Mapping on computers on the local area networks (LANs) as other computers running Windows Services for UNIX can help ensure a high level of performance. Even if your network is not geographically dispersed, you might want to run User Name Mapping on more than one computer to improve performance and availability.
When you run User Name Mapping on multiple computers, you can create a pool of servers using Domain Name System (DNS) round robin. Doing this provides a number of benefits:
The first step in creating a User Name Mapping server pool is to install User Name Mapping on two or more servers. These servers must be configured and maintained identically to ensure that they provide consistent responses to mapping requests. The easiest way to do this is to use batch (.cmd) files that repeat the same mapadmin command for each server in the pool.
For example, you could install User Name Mapping on three servers named UNM1, UNM2, and UNM3. You would then create a batch file that would apply the same mapadmin command and arguments to all three servers:
REM POOLADMIN.CMD
REM Used to administer three User Name Mapping servers: UNM1, UNM2, and UNM3
REM Syntax: POOLADMIN mapadmin_argument[...]
mapadmin UNM1 %0 %1 %2 %3 %4 %5 %6 %7 %8 %9 -u UNM1\administrator -p admUNM1pwd
mapadmin UNM2 %0 %1 %2 %3 %4 %5 %6 %7 %8 %9 -u UNM2\administrator -p admUNM2pwd
mapadmin UNM3 %0 %1 %2 %3 %4 %5 %6 %7 %8 %9 -u UNM3\administrator -p admUNM3pwd
Use a file like this, or a similar technique, to configure and administer all the User Name Mapping servers in the pool, both before and after the pool has been created.
Once you have set up and configured the servers that will belong to the pool, the next step is to create the pool itself. You do this by configuring a DNS server to map a single name to the Internet Protocol (IP) addresses of all three User Name Mapping servers. For example, you could map the name UNMpool to the IP addresses for UNM1, UNM2, and UNM3. Whenever a client computer asks the DNS server to resolve the name UNMpool, the DNS server will return all three IP addresses, the first of which is the one most clients will use. Because the DNS server rotates (in a round-robin fashion) the order in which it returns the three IP addresses, this automatically provides for load balancing.
The final step in setting up a User Name Mapping pool is to configure computers on the network running Interix, Client for NFS, Server for NFS, and Remote Shell service to use the virtual server name of the pool (UNMpool in the example). Because the DNS server rotates the order of the IP addresses it returns when it resolves this name, each of these User Name Mapping clients will receive a different primary IP address than the one given to the previous client, thereby automatically providing load balancing among the three User Name Mapping servers. In addition, these Windows Services for UNIX components are designed to send mapping requests to each IP address it receives if requests to the previous IP address times out. This provides for automatic failover if one of the servers in the pool should fail.
As noted earlier, it is essential that all servers that belong to a pool are configured and maintained identically. If PCNFS passwd and group files are used to provide UNIX account information for mapping users, for example, identical passwd and group files must be copied to and maintained on all servers in the pool, and if you restore data from a backup file, the passwd and group files that are restored to the %sfudir%\PCNFS or %temp% directory must be copied to the appropriate location for all servers in the pool. (Note that when files are restored on the computer from which they were backed up, the passwd and group files are restored to %sfudir%\PCNFS, regardless of their original location, and User Name Mapping is configured to use the files at that location.) Similarly, if you use .maphosts files to control access to servers in the pool, you must maintain identical .maphosts files on all servers in the pool.