A journal service manages a journal that holds a number of journal entries. Journal entries are provided to the journal service by one or more producer services, and the journal service provides journal entries to one or more consumer services. Lead consumers retrieve journal entries from the journal service by specifying a named cursor which identifies a location within the journal from which the journal entries are retrieved. The journal service may select a lead producer and a lead consumer from a collection of candidate producers and consumers using a fitness score determined for each candidate producer and consumer. The fitness score may be based at least in part on the processing capability, predicted reliability, and cost of each candidate producer and consumer. The journal service may replace a lead consumer or producer with an alternate consumer or producer in response to a variety of events.