Methods and apparatus for supporting customer-directed networking limits in distributed systems are disclosed. A client request is received via a programmatic interface, indicating a particular lower resource usage limit to be imposed on at least one category of network traffic at a particular instance of a network-accessible service. Resource usage metrics for one or more categories of network traffic at the particular instance are obtained. In response to a determination that resource usage at the particular instance has reached a threshold level, one or more responsive actions are initiated.