Create a function triggered by Azure Cosmos DB

Learn how to create a function triggered when data is added to or changed in Azure Cosmos DB. To learn more about Azure Cosmos DB, see Azure Cosmos DB: Serverless database computing using Azure Functions.

View message in the logs.


To complete this tutorial:

  • If you don't have an Azure subscription, create a free account before you begin.

Create an Azure Function app

  1. Select the New button found on the upper left-hand corner of the Azure portal, then select Compute > Function App.

    Create a function app in the Azure portal

  2. Use the function app settings as specified in the table below the image.

    Define new function app settings

    Setting Suggested value Description
    App name Globally unique name Name that identifies your new function app. Valid characters are a-z, 0-9, and -.
    Subscription Your subscription The subscription under which this new function app is created.
    Resource Group myResourceGroup Name for the new resource group in which to create your function app.
    OS Windows Serverless hosting is currently only available when running on Windows. For Linux hosting, see Create your first function running on Linux using the Azure CLI.
    Hosting plan Consumption plan Hosting plan that defines how resources are allocated to your function app. In the default Consumption Plan, resources are added dynamically as required by your functions. In this serverless hosting, you only pay for the time your functions run. When you run in an App Service plan, you must manage the scaling of your function app.
    Location West Europe Choose a region near you or near other services your functions access.
    Storage account Globally unique name Name of the new storage account used by your function app. Storage account names must be between 3 and 24 characters in length and may contain numbers and lowercase letters only. You can also use an existing account, which must meets the storage account requirements.
  3. Select Create to provision and deploy the function app.

  4. Select the Notification icon in the upper-right corner of the portal and watch for the Deployment succeeded message.

    Define new function app settings

  5. Select Go to resource to view your new function app.


Having trouble finding your function apps in the portal, try adding Function Apps to your favorites in the Azure portal.

Next, you create a function in the new function app.

Create Azure Cosmos DB trigger

  1. Expand your function app and click the + button next to Functions. If this is the first function in your function app, select Custom function. This displays the complete set of function templates.

    Functions quickstart page in the Azure portal

  2. In the search field, type cosmos and then choose your desired language for the Azure Cosmos DB trigger template.

    Choose the Azure Cosmos DB trigger

  3. Configure the new trigger with the settings as specified in the table below the image.

    Create the Azure Cosmos DB triggered function

    Setting Suggested value Description
    Name Default Use the default function name suggested by the template.
    Collection name Items Name of collection to be monitored.
    Create lease collection if it doesn't exist Checked The collection doesn't already exist, so create it.
    Database name Tasks Name of database with the collection to be monitored.
  4. Select New next to the Azure Cosmos DB account connection label, and choose an existing Cosmos DB account or + Create new.

    Configure Azure Cosmos DB connection

  5. When creating a new Cosmos DB account, use the New account settings as specified in the table.

    Setting Suggested value Description
    ID Name of database Unique ID for the Azure Cosmos DB database
    API SQL This topic uses the SQL API.
    Subscription Azure Subscription The subscription under which this new Cosmos DB account is created.
    Resource Group myResourceGroup Use the existing resource group that contains your function app.
    Location WestEurope Select a location near to either your function app or to other apps that use the stored documents.
  6. Click OK to create the database. It may take a few minutes to create the database. After the database is created, the database connection string is stored as a function app setting. The name of this app setting is inserted in Azure Cosmos DB account connection.

  7. Click Create to create your Azure Cosmos DB triggered function. After the function is created, the template-based function code is displayed.

    Cosmos DB function template in C#

    This function template writes the number of documents and the first document ID to the logs.

Next, you connect to your Azure Cosmos DB account and create the Tasks collection in the database.

Create the Items collection

  1. Open a second instance of the Azure portal in a new tab in the browser.

  2. On the left side of the portal, expand the icon bar, type cosmos in the search field, and select Azure Cosmos DB.

    Search for the Azure Cosmos DB service

  3. Choose your Azure Cosmos DB account, then select the Data Explorer.

  4. In Collections, choose taskDatabase and select New Collection.

    Create a collection

  5. In Add Collection, use the settings shown in the table below the image.

    Define the taskCollection

    Setting Suggested value Description
    Database ID Tasks The name for your new database. This must match the name defined in your function binding.
    Collection ID Items The name for the new collection. This must match the name defined in your function binding.
    Storage capacity Fixed (10 GB) Use the default value. This value is the storage capacity of the database.
    Throughput 400 RU Use the default value. If you want to reduce latency, you can scale up the throughput later.
    Partition key /category A partition key that distributes data evenly to each partition. Selecting the correct partition key is important in creating a performant collection.
  6. Click OK to create the Tasks collection. It may take a short time for the collection to get created.

After the collection specified in the function binding exists, you can test the function by adding documents to this new collection.

Test the function

  1. Expand the new taskCollection collection in Data Explorer, choose Documents, then select New Document.

    Create a document in taskCollection

  2. Replace the contents of the new document with the following content, then choose Save.

         "id": "task1",
         "category": "general",
         "description": "some task"
  3. Switch to the first browser tab that contains your function in the portal. Expand the function logs and verify that the new document has triggered the function. See that the task1 document ID value is written to the logs.

    View message in the logs.

  4. (Optional) Go back to your document, make a change, and click Update. Then, go back to the function logs and verify that the update has also triggered the function.

Clean up resources

Other quick starts in this collection build upon this quick start. If you plan to work with subsequent quick starts, tutorials, or with any of the services you have created in this quick start, do not clean up the resources.

Resources in Azure refers to function apps, functions, storage accounts, and so forth. They are grouped into resource groups, and you can delete everything in a group by deleting the group.

You created resources to complete these quickstarts. You may be billed for these resources, depending on your account status and service pricing. If you don't need the resources anymore, here's how to delete them:

  1. In the Azure portal, go to the Resource group page.

    To get to that page from the function app page, select the Overview tab and then select the link under Resource group.

    Select the resource group to delete from the function app page.

    To get to that page from the dashboard, select Resource groups, and then select the resource group that you used for this quickstart.

  2. In the Resource group page, review the list of included resources, and verify that they are the ones you want to delete.

  3. Select Delete resource group, and follow the instructions.

    Deletion may take a couple of minutes. When it's done, a notification appears for a few seconds. You can also select the bell icon at the top of the page to view the notification.

Next steps

You have created a function that runs when a document is added or modified in your Azure Cosmos DB.

Learn how to create functions with other kinds of triggers or how to integrate functions with other Azure services.

For more information about Azure Cosmos DB triggers, see Azure Cosmos DB bindings for Azure Functions.