Share RUs with a Serverless Function
A popular pattern is to build a REST API using serverless Function with Http trigger, backed by Cosmos DB. Serverless is a very popular paradigm, and Cosmos is the best cloud database, so it's no wonder that customers are interested in this combination. However, the problem in this scenario is the cold start of the serverless Function, which negates the low-latency benefits of CosmosDB provisioning.
It would be great to allow sharing the RUs provisioned for Cosmos DB collection with serverless functions running against the same collection. Let the Function execution consume some extra RUs, depending on the complexity of the Function -- similar to how current Consumption billing works for Functions. But keep such Function "Always On" to avoid cold start, and allow the users to enjoy the benefits of sub-10ms latency in their REST API.
This is not something that we are currently looking at doing.
We currently have premium functions available that remove the cold start challenge and hopefully would meet your current needs.