1. A method for facilitating an upgrade of a cluster of servers in the presence of one or more inaccessible nodes in the cluster, comprising: upgrading a version of a distributed software program on each of a plurality of nodes in the cluster; detecting that one or more nodes of the cluster are inaccessible; continuing to upgrade nodes in the cluster other than the one or more nodes that were detected to be inaccessible, wherein the upgrading involves installing and activating a newer version of the distributed software on the nodes being upgraded; and upgrading an acting version of the cluster.