I work for MongoDB. The writer is referring to CosmosDB, the Microsoft clone of MongoDB. You can runa real MongoDB cluster on Azure with MongoDB Atlas. The pricing model for Atlas is per Node size + disk + memory + data transfer. It's generally easier to predict your costs using this model. Users tend to over-provision with this model so we recommend using auto-scaling. This will allow your cluster to scale up or down based on load (price will adjust as well).
