Connecting Azure Functions to Cosmos DB

Azure Functions

Cosmos DB works exceptionally well in a serverless architecture thanks to its change feed and binding for Azure Functions. In this lesson, we’ll see a realistic example of architecture and code for the following:

• Triggers

• Input binding

• Output binding

Triggers

A trigger starts an Azure Function. For example, a trigger can be an HTTP request or a timer. In our case, we want to listen to container changes, and to do so, we need to use CosmosDBTrigger. The function is called automatically when documents change in a container.

The trigger requires some parameters to work:

• databaseName: This is the name of the Cosmos DB database.

• containerName: This is the name of the container.

• connection: This is the name of the setting that contains the connection string.

The following are other optional parameters that can be useful:

• LeaseContainerName: The name of the container lease information is stored (optional, default: "leases")

• LeaseDatabaseName: The name of the database lease information is stored (optional, default: databaseName)

• CreateLeaseContainerIfNotExists: If true, it creates the lease collection automatically (optional, false).

• LeaseContainerPrefix: Consumer prefix in case we want to use the same lease container for multiple independent consumers

Note: We are referring to Microsoft.Azure.WebJobs.Extensions.CosmosDB v4, which uses Microsoft.Azure.Cosmos v3.

Let’s see a basic example: a trigger for our iotEvents container.