Metadata indicating that an action implementation node and a routing decision master node have been assigned to a virtual traffic hub programmatically associated with one or more isolated networks is stored. The routing decision master node determines a first action to be implemented for packets of a network flow using state information of the isolated networks, and provides a representation of a first action to the first action implementation node. Based on performing the first action at the action implementation node, contents of a data packet received from one isolated network are transmitted to another isolated network.