What is Azure Cosmos DB for MongoDB?


Azure Cosmos DB is a fully managed NoSQL and relational database for modern app development.

Azure Cosmos DB for MongoDB makes it easy to use Azure Cosmos DB as if it were a MongoDB database. You can use your existing MongoDB skills and continue to use your favorite MongoDB drivers, SDKs, and tools by pointing your application to the connection string for your account using the API for MongoDB.


Want to try the Azure Cosmos DB for MongoDB with no commitment? Create an Azure Cosmos DB account using Try Azure Cosmos DB for free.

Cosmos DB for MongoDB benefits

Cosmos DB for MongoDB has numerous benefits compared to other MongoDB service offerings such as MongoDB Atlas:

  • Instantaneous scalability: With the Autoscale feature, your database scales instantaneously with zero warmup period. Other MongoDB offerings such as MongoDB Atlas can take hours to scale up and up to days to scale down.

  • Automatic and transparent sharding: The API for MongoDB manages all of the infrastructure for you. This management includes sharding and optimizing the number of shards. Other MongoDB offerings such as MongoDB Atlas, require you to specify and manage sharding to horizontally scale. This automation gives you more time to focus on developing applications for your users.

  • Five 9's of availability: 99.999% availability is easily configurable to ensure your data is always there for you.

  • Active-active database: Unlike MongoDB Atlas, Cosmos DB for MongoDB supports active-active across multiple regions. Databases can span multiple regions, with no single point of failure for writes and reads for the same data. MongoDB Atlas global clusters only support active-passive deployments for writes for the same data.

  • Cost efficient, granular, unlimited scalability: Sharded collections can scale to any size, unlike other MongoDB service offerings. The Azure Cosmos DB platform can scale in increments as small as 1/100th of a VM due to its architecture. This means that you can scale your database to the exact size you need, without paying for unused resources.

  • Real time analytics (HTAP) at any scale: Run analytics workloads against your transactional MongoDB data in real time with no effect on your database. This analysis is fast and inexpensive, due to the cloud native analytical columnar store being utilized, with no ETL pipelines. Easily create Power BI dashboards, integrate with Azure Machine Learning and Azure Cognitive Services, and bring all of your data from your MongoDB workloads into a single data warehousing solution. Learn more about the Azure Synapse Link.

  • Serverless deployments: Cosmos DB for MongoDB offers a serverless capacity mode. With Serverless, you're only charged per operation, and don't pay for the database when you don't use it.

  • Free Tier: With Azure Cosmos DB free tier, you get the first 1000 RU/s and 25 GB of storage in your account for free forever, applied at the account level. Free tier accounts are automatically sandboxed so you never pay for usage.

  • Free 7 day Continuous Backups: Azure Cosmos DB for MongoDB offers free 7 day continuous backups for any amount of data. This means that you can restore your database to any point in time within the last 7 days.

  • Upgrades take seconds: All API versions are contained within one codebase, making version changes as simple as flipping a switch, with zero downtime.

  • Role Based Access Control: With Azure Cosmos DB for MongoDB, you can assign granular roles and permissions to users to control access to your data and audit user actions- all using native Azure tooling.

  • Flexible single-field indexes: Unlike single field indexes in MongoDB Atlas, single field indexes in Cosmos DB for MongoDB cover multi-field filter queries. There is no need to create compound indexes for each multi-field filter query. This increases developer productivity.

  • In-depth monitoring capabilities: Cosmos DB for MongoDB integrates natively with Azure Monitor to provide in-depth monitoring capabilities.

How Cosmos DB for MongoDB works

Cosmos DB for MongoDB implements the wire protocol for MongoDB. This implementation allows transparent compatibility with MongoDB client SDKs, drivers, and tools. Azure Cosmos DB doesn't host the MongoDB database engine. Any MongoDB client driver compatible with the API version you're using should be able to connect, with no special configuration.


This article describes a feature of Azure Cosmos DB that provides wire protocol compatibility with MongoDB databases. Microsoft does not run MongoDB databases to provide this service. Azure Cosmos DB is not affiliated with MongoDB, Inc.

MongoDB feature compatibility

Cosmos DB for MongoDB is compatible with the following MongoDB server versions:

Choosing a server version

All versions run on the same codebase, making upgrades a simple task that can be completed in seconds with zero downtime. Azure Cosmos DB simply flips a few feature flags to go from one version to another. The feature flags also enable continued support for older API versions such as 3.2 and 3.6. You can choose the server version that works best for you.

Not sure if your workload is ready? Reach out to us to leverage automated tooling to determine if you're ready to migrate to Cosmos DB for MongoDB.

What you need to know to get started

  • You aren't billed for virtual machines in a cluster. Pricing is based on throughput in request units (RUs) configured on a per database or per collection basis. The first 1000 RUs per second are free with Free Tier.

  • There are three ways to deploy the Cosmos DB for MongoDB:

    • Provisioned throughput: Set a RU/sec number and change it manually. This model best fits consistent workloads.

    • Autoscale: Set an upper bound on the throughput you need. Throughput instantly scales to match your needs. This model best fits workloads that change frequently and optimizes their costs.

    • Serverless: Only pay for the throughput you use, period. This model best fits dev/test workloads.

  • Sharded cluster performance is dependent on the shard key you choose when creating a collection. Choose a shard key carefully to ensure that your data is evenly distributed across shards.

Frequently asked questions

  1. Does Cosmos DB for MongoDB support my data residency requirements?

    Yes, data residency is governed at the database account level which is associated with one or more regions. Customers typically create a database account for each residency requirement. For example, if you have a requirement to store data in the US and EU, you would create two database accounts, one in the US and one in the EU.

  2. Does Cosmos DB for MongoDB support documents larger than 2 MB?

    Yes, documents as large as 16 MB are fully supported.

  3. Does Cosmos DB for MongoDB support multi-field sort?

    Yes, multi-field sort is supported. A compound index is required for the fields in the sort to ensure the operation is efficient and scalable.

  4. Does Cosmos DB for MongoDB scale linearly?

    In many cases, Cosmos DB's costs scale better than linear. For example, if you read a 1KB document, this equates to 1 Request Unit (RU). But if you read a 10KB document, this still equates to roughly 1RU. The Cosmos DB capacity calculator can help you estimate your throughput needs.

  5. How can I encrypt data and manage access at the field level?

    Cosmos DB for MongoDB supports Field Level Encryption.

  6. How do I pay for Request Units (RUs)?

    Cosmos DB for MongoDB offers three capacity modes: provisioned throughput, autoscale, and serverless. None require an upfront commitment. Autoscale instantaneously scales to meet your needs, and serverless only charges for the throughput you use.

  7. Which features are supported in Cosmos DB for MongoDB?

    Cosmos DB for MongoDB supports a rich set of MongoDB features backed by Cosmos DB's limitless scale architecture. These features include: Aggregation pipelines, Change streams, Indexes, Geospatial queries, and more. See the feature support matrix for more details. Not sure if your workload is ready? Reach out to us to leverage automated tooling to determine if you're ready to migrate to Cosmos DB for MongoDB.

  8. Does Cosmos DB for MongoDB run on-premises?

    Cosmos DB for MongoDB is a cloud-native multi-tenant service and is not available on-premises. Cosmos DB offers an emulator for local development and testing.

Next steps