AZ-305 Design data storage solutions Practice Question

Answer analysis

Option-by-option breakdown

For each option: why learners choose it and why it is or isn't the right answer here.

• ✗

  Azure SQL Database

  Why it's wrong here

  Azure SQL Database is a relational database engine built on SQL Server technology, using T-SQL for queries and enforcing a fixed schema with tables, rows, and columns. It does not implement the MongoDB wire protocol, BSON document storage, or MongoDB query operators, so MongoDB client drivers and tools cannot connect to it. Attempting to use it as a MongoDB-compatible service would require a complete data model redesign and application rewrite, making it incorrect for hosting a MongoDB-compatible workload.

• ✓

  Azure Cosmos DB API for MongoDB

  Why this is correct

  Azure Cosmos DB API for MongoDB is a first-party Azure service that implements the MongoDB wire protocol, allowing existing MongoDB SDKs, drivers, and tools to connect directly. It provides MongoDB-compatible CRUD operations, indexing, aggregation pipelines, and sharding semantics while adding Azure-native capabilities such as global distribution, multi-region writes, automatic failover, and flexible consistency levels. Because it is natively integrated with Azure Portal, ARM templates, and Azure CLI, it is a correct and widely recommended choice for hosting MongoDB-compatible workloads on Azure.

• ✗

  Azure Database for PostgreSQL

  Why it's wrong here

  Azure Database for PostgreSQL is a fully managed relational database that uses SQL and the PostgreSQL wire protocol, storing data in tables with relational integrity and transactions. Although PostgreSQL offers JSON/JSONB data types, it does not understand MongoDB's BSON format, query language, or wire protocol, so MongoDB clients cannot communicate with it. Its query engine, indexing behavior, and partitioning model are fundamentally different from MongoDB, making it unsuitable for hosting a MongoDB-compatible service without substantial application changes.

• ✓

  Azure Database for MongoDB (MongoDB Atlas on Azure)

  Why this is correct

  Azure Database for MongoDB, also known as MongoDB Atlas on Azure, is a fully managed MongoDB-compatible database service operated by MongoDB, Inc. and delivered through the Azure Marketplace. It gives you the original MongoDB server engine (community or enterprise edition) with native MongoDB features such as document model, replicasets, sharded clusters, and Mongo shell compatibility, while integrating with Azure networking and single sign-on. As a true MongoDB service (not an emulation), it is a correct answer and often preferable when you want the exact MongoDB behavior and tooling without any API-level translation.

• ✗

  Azure Cache for Redis

  Why it's wrong here

  Azure Cache for Redis is an in-memory key-value data store based on the open-source Redis engine, optimized for caching, session state, message brokering, and transient data. Its data structures are limited to strings, hashes, lists, sets, and sorted sets, and it has no concept of BSON documents, database collections, or MongoDB aggregation pipelines. Since it doesn't expose the MongoDB wire protocol or document query capabilities, it is entirely unsuitable as a MongoDB-compatible host and is clearly incorrect for this scenario.

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