Cosmos DB is the new NoSQL database released in Azure Cloud by Microsoft. Unlike relational databases, Cosmos DB is scalable as it is a hosted database service, so it enjoys a lot of popularity among high transaction .NET and .NET Core applications.
However, using Cosmos DB, you need to be wary of performance bottlenecks and cost overhead for accessing the database as Microsoft charges you for each transaction to Cosmos DB. While Cosmos DB is scalable in terms of transaction capacity, it is not as fast because the database service is living in a separate VNet or subscription than the applications. So even if your applications are running in Azure cloud, accessing the database across the VNet is a huge blow to the performance.