Configuring aufs for a Cluster

Benefits of using aufs

aufs is software that allows for union mounting filesystems in Linux. Union mounting combines two or more separate filesystems at a single mount point. Usually one of the filesystems is mounted read-write, while the other is mounted read-only. Changes made in the union are saved to the read-write filesystem, while the read-only filesystem remains unchanged. This allows the union to be modified freely, even while most of the underlying filesystem is read-only. This technique is used in live-cd distributions to save modifications to RAM.

This can be a very powerful tool in a cluster environment, because cluster nodes can mount a large read-only filesystem over NFS, while storing any local runtime modifications in RAM or on the local hard disk. There is no fear of nodes modifying the root NFS, nodes can be updated instantly by simply updating the root NFS, and software on the nodes run as expected because the filesystem can be treated as read-write.

Installing aufs on the Node Chroot

In order to use aufs, nodes need to boot a kernel with aufs support, and the userland utilities need to be installed in the node chroot.