A server at a cluster of servers in a data center is described. The server comprises a memory which is part of a distributed memory of the cluster. The server has at least one processor executing transactions and lock-free reads on software objects stored in regions of the distributed memory, the software objects and details of the transactions being replicated in the distributed memory. The server has a network interface card arranged to receive a message indicating a new configuration of the cluster comprising addition, removal or potential failure of at least one of the other servers. The processor is configured to use a recovery process which enables the lock-free reads and committed ones of the transactions to retain the properties of atomicity, consistency, isolation and durability across configuration changes.