What is the Azure Cosmos DB emulator?

The Azure Cosmos DB emulator provides a local environment that emulates the Azure Cosmos DB service designed for development purposes. Using the emulator, you can develop and test your application locally, without creating an Azure subscription or incurring any service costs. When you're satisfied with how your application is working with the emulator, you can transition to using an Azure Cosmos DB account with minimal friction.

Differences between the emulator and cloud service

The emulator provides an environment on your developer workspace that isn't capable of emulating every aspect of the Azure Cosmos DB service. Here are a few key differences in functionality between the emulator and the equivalent cloud service.

• The emulator's Data Explorer pane is only supported in the API for NoSQL and API for MongoDB.
• The emulator only supports provisioned throughput. The emulator doesn't support serverless throughput.
• The emulator uses a well-known key when it starts. You can't regenerate the key for the running emulator. To use a different key, you must start the emulator with the custom key specified.
• The emulator can't be replicated across geographical regions or multiple instances. Only a single running instance of the emulator is supported. The emulator can't be scaled out.
• The emulator ideally supports up to 10 fixed-size containers at 400 RU/s or 5 unlimited-size containers. Theoretically, you can create more containers, but you could experience performance degradation with the emulator.
• The emulator only supports the Session and Strong consistency levels. The emulator isn't a scalable service and doesn't actually implement the consistency levels. The emulator only flags the configured consistency level for testing purposes.
• The emulator constraints the unique identifier of items to a size of 254 characters.
• The emulator supports a maximum of five JOIN statements per query.

The emulator's features may lag behind the pace of new features for the cloud service. There could potentially be new features and changes in the cloud service that have a small delay before they're available in the emulator.

Authentication

Every request made against the emulator must be authenticated using a key over TLS/SSL. The emulator ships with a single account configured to use a well-known authentication key. By default, these credentials are the only credentials permitted for use with the emulator:

Import emulator certificate

In some cases, you may wish to manually import the TLS/SS certificate from the emulator's running container into your host machine. This step avoids bad practices like disabling TLS/SSL validation in the SDK. For more information, see import certificate.

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