Azure Serverless Computing Cookbook - Second Edition

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When you integrate Azure Functions to track Cosmos DB changes, it will automatically create a new collection named leases, as shown in the following screenshot. Be aware that this is an additional cost as the cost in Cosmos DB is based on the request units (RUs) that are allocated for each collection:

It's important to note that the Cosmos DB trigger won't be triggered (at the time of writing) for any deletes in the collection. It is only triggered for create and updates to documents in a collection. If it is important for you to track deletes, then you need to do soft deletes, which means setting an attribute such as isDeleted ...