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How Azure DocumentDB Turns PostgreSQL into a MongoDB-Compatible Cloud Database
A layer-by-layer technical walkthrough of a MongoDB-compatible, PostgreSQL-based document database, from the open engine to the managed cloud service.
This article is a technical walkthrough of how Azure DocumentDB is built, from the open-source engine at its core to the managed service that runs it in the cloud. I trace the full stack in order: PostgreSQL as the foundation, the MongoDB-compatible document layer on top of it, the Kubernetes operator that lets the same database run anywhere, and the Azure managed features that handle storage, performance, high availability, and multi-cloud replication. Along the way, I use published cost and performance numbers to show where the design choices pay off.
By the end, you will have a clear model of each layer, how the layers fit together, and when reaching for the managed service makes more sense than running the open engine yourself.
A quick grounding first. Azure DocumentDB is the fully managed service that was previously called the vCore-based Azure Cosmos DB for MongoDB, and it reached general availability in November 2025.
