Abstract: Some examples described herein relate to cluster formation. In an example, on a cluster management system, a cluster formation image may be provided for forming a cluster of nodes. The cluster formation image may comprise a compressed version of an operating system, and a plan script comprising custom attributes for customizing the operating system and instructions for forming the cluster. In response to a selection of the cluster formation image, the cluster formation image may be provided from the cluster management system to each of the nodes. The operating system may be installed on each of the nodes, and the operating system on each of the nodes may be customized based on the custom attributes in the plan script. The nodes may be formed into a cluster based on the instructions in the plan script.