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: receiving an instruction to upgrade an older version of a distributed software program installed on each of a plurality of nodes forming the cluster; installing and activating a newer version of the distributed software program on a subset of the plurality of nodes, the subset having fewer nodes than the entire cluster, and the subset of the plurality of nodes continuing to operate according to an older acting version of the distributed software program; receiving an instruction to forcibly upgrade the cluster; and upgrading the cluster so that the subset of nodes cease to operate according to the older acting version of the distributed software program and begin to operate according to a newer acting version of the distributed software program, wherein each node remains a member of the cluster during the upgrade, and wherein the newer version of the distributed software program can operate according to the older acting version corresponding to the older version of the distributed software program, and can also operate according to the newer acting version of the distributed software program.