1. A computer-implemented method comprising: providing, by one or more programmed computing systems of a configurable network service, a first virtual computer network having multiple computing nodes by overlaying the first virtual computer network on a distinct substrate network that interconnects the multiple computing nodes; maintaining, by the one or more programmed computing systems, a second computing node of the multiple computing nodes as a replicated copy of a first computing node of the multiple computing nodes, the maintaining including dynamically updating the second computing node to reflect changes in state of the first computing node as the first computing node performs operations for the first virtual computer network; maintaining, by the one or more programmed computing systems, mapping information related to a first network location in the substrate network of the first computing node and to a second network location in the substrate network of the second computing node, the maintained mapping information including an association of the second computing node with the first computing node; and determining, by the one or more programmed computing systems, to use the second computing node in place of the first computing node; and at a time after the determining to use the second computing node in place of the first computing node, managing, by the one or more programmed computing systems, one or more communications directed to the first computing node by redirecting the one or more communications to the second computing node in place of the first computing node.