Client Failover

We saw earlier that NFS supports server redundancy by providing a failover feature, and mentioned that it is also supported with Autofs. All we need to do to add this support is to list the alternative servers in the map.

We'll do this for the manual pages. The map is shown below after we have made the modifications:

lithium# cat /etc/auto_man
/usr/share/man -ro neon,carbon,nitrogen:/usr/share/man
lithium#

In this case, we now have three servers that are able to supply the data we require. The order in which each server will be used depends on a number of factors, such as network location, response time, and the level of the NFS protocol that is supported. The fact that response time is considered helps with load balancing, to some extent, as the most heavily loaded server will respond later and so is less likely to be chosen.

Preferred Servers and Weighting

If we want to define which server becomes our preferred one, we can add some weighting to it, although this will only be considered after the above factors have been taken into account. Our preferred order is neon, followed by carbon, followed by nitrogen. Adding some weighting, we get the following map:

lithium# cat /etc/auto_man
/usr/share/man -ro neon,carbon(1),nitrogen(2):/usr/share/man
lithium#

This shows that, the higher the weighting, the less chance the server will be selected.