You should again read LAM documentation about configuring your farm. I went for the simplest solution. My LAM is installed under Solaris 2.3 in /opt/lam. There is a subdirectory there called /opt/lam/boot. In that directory there is a file bhost.def, and that file looks as follows
gustav@cisr:/opt/lam/boot 236 $ cat bhost.def # # Ohio Trollius # # Function: - bhost.def # - CISR LAM system # cisr mercury venus earth mars jupiter saturn uranus bacchus ceres diana minerva vesta gustav@cisr:/opt/lam/boot 237 $It simply lists the names of machines in our Solaris farm. That's all you need to do.
You can have a more elaborate set up with weights and topologies. This is also described in LAM documents.