A method, system and article of manufacture for upgrade of a software module executed in a distributed software computer system using shadow installations of software modules for minimum downtime. A first software module is executed on a first host and a second software module is executed on a second host, the two software modules in communication with each other. Target release of the first software module and a local release of the second software module are installed and deployed on the first host during the execution of the first software module. The first software module is switched to the target release in communication with the local release of the second software module. The communication with the second software module is reestablished after the upgrade.