Create a function triggered by Azure Cosmos DB

Learn how to create a function in the Azure portal that is 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.

Prerequisites

To complete this tutorial:

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

Sign in to Azure

Sign in to the Azure portal with your Azure account.

Create an Azure Cosmos DB account

You must have an Azure Cosmos DB account that uses the SQL API before you create the trigger.

1. From the Azure portal menu or the Home page, select Create a resource.

2. Search for Azure Cosmos DB. Select Create > Azure Cosmos DB.

3. In the Create Azure Cosmos DB Account page, enter the basic settings for the new Azure Cosmos DB account.

   Setting	Value	Description
   Subscription	Subscription name	Select the Azure subscription that you want to use for this Azure Cosmos DB account.
   Resource Group	Resource group name	Select a resource group, or select Create new, then enter a unique name for the new resource group.
   Account Name	A unique name	Enter a name to identify your Azure Cosmos DB account. Because documents.azure.cn is appended to the name that you provide to create your URI, use a unique name. The name can contain only lowercase letters, numbers, and the hyphen (-) character. It must be 3-44 characters.
   API	NoSQL	The API determines the type of account to create. Azure Cosmos DB provides five APIs: NoSQL for document databases, Gremlin for graph databases, MongoDB for document databases, Azure Table, and Cassandra. To learn more about the API for NoSQL, see Welcome to Azure Cosmos DB.
   Location	The region closest to your users	Select a geographic location to host your Azure Cosmos DB account. Use the location that is closest to your users to give them the fastest access to the data.
   Capacity mode	Provisioned throughput or Serverless	Select Provisioned throughput to create an account in provisioned throughput mode. Select Serverless to create an account in serverless mode.
   Apply Azure Cosmos DB free tier discount	Apply or Do not apply	With Azure Cosmos DB free tier, you get the first 1000 RU/s and 25 GB of storage for free in an account. Learn more about free tier.
   Limit total account throughput	Selected or not	Limit the total amount of throughput that can be provisioned on this account. This limit prevents unexpected charges related to provisioned throughput. You can update or remove this limit after your account is created.

   You can have up to one free tier Azure Cosmos DB account per Azure subscription and must opt in when creating the account. If you don't see the option to apply the free tier discount, another account in the subscription has already been enabled with free tier.

   

   Note

   The following options are not available if you select Serverless as the Capacity mode:

   • Apply Free Tier Discount
   • Limit total account throughput

4. In the Global Distribution tab, configure the following details. You can leave the default values for this quickstart:

   Setting	Value	Description
   Geo-Redundancy	Disable	Enable or disable multiple-region distribution on your account by pairing your region with a pair region. You can add more regions to your account later.
   Multi-region Writes	Disable	Multi-region writes capability allows you to take advantage of the provisioned throughput for your databases and containers across China.
   Availability Zones	Disable	Availability Zones help you further improve availability and resiliency of your application.

   Note

   The following options are not available if you select Serverless as the Capacity mode in the previous Basics page:

   • Geo-redundancy
   • Multi-region Writes

5. Optionally, you can configure more details in the following tabs:

   • Networking. Configure access from a virtual network.
   • Backup Policy. Configure either periodic or continuous backup policy.
   • Encryption. Use either service-managed key or a customer-managed key.
   • Tags. Tags are name/value pairs that enable you to categorize resources and view consolidated billing by applying the same tag to multiple resources and resource groups.

6. Select Review + create.

7. Review the account settings, and then select Create. It takes a few minutes to create the account. Wait for the portal page to display Your deployment is complete.

   

8. Select Go to resource to go to the Azure Cosmos DB account page.

   

Create a function app in Azure

1. From the Azure portal menu or the Home page, select Create a resource.

2. In the New page, select Compute > Function App.

3. On the Basics page, use the function app settings as specified in the following table:

   Setting	Suggested value	Description
   Subscription	Your subscription	The subscription under which you'll create your new function app.
   Resource Group	myResourceGroup	Name for the new resource group in which you'll create your function app. You should create a new resource group because there are known limitations when creating new function apps in an existing resource group.
   Function App name	Globally unique name	Name that identifies your new function app. Valid characters are a-z (case insensitive), 0-9, and -.
   Publish	Code	Option to publish code files or a Docker container.
   Runtime stack	Preferred language	Choose a runtime that supports your favorite function programming language. In-portal editing is only available for JavaScript, PowerShell, TypeScript, and C# script. C# class library, Java, and Python functions must be developed locally.
   Version	Version number	Choose the version of your installed runtime.
   Region	Preferred region	Select a region that's near you or near other services that your functions can access.

4. Select Next : Hosting. On the Hosting page, enter the following settings:

   Setting	Suggested value	Description
   Storage account	Globally unique name	Create a storage account used by your function app. Storage account names must be between 3 and 24 characters in length and can contain numbers and lowercase letters only. You can also use an existing account, which must meet the storage account requirements.
   Operating system	Windows	An operating system is pre-selected for you based on your runtime stack selection, but you can change the setting if necessary. In-portal editing is only supported on Windows.
   Plan	Consumption (Serverless)	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 pay only for the time your functions run. When you run in an App Service plan, you must manage the scaling of your function app.

5. Select Next : Monitoring. On the Monitoring page, enter the following settings:

   Setting	Suggested value	Description
   Application Insights	Default	Creates an Application Insights resource of the same App name in the nearest supported region. By expanding this setting or selecting Create new, you can change the Application Insights name or select a different region in an Azure geography where you want to store your data.

6. Select Review + create to review the app configuration selections.

7. On the Review + create page, review your settings, and then select Create to provision and deploy the function app.

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

9. Select Go to resource to view your new function app. You can also select Pin to dashboard. Pinning makes it easier to return to this function app resource from your dashboard.

   

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

Create Azure Cosmos DB trigger

1. In your function app, select Overview, and then select + Create under Functions.

2. Under Select a template, scroll down and choose the Azure Cosmos DB trigger template.

3. In Template details, configure the new trigger with the settings as specified in this table, then select Create:

   Setting	Suggested value	Description
   New function	Accept the default name	The name of the function.
   Azure Cosmos DB account connection	Accept the default new name	Select New, the Database Account you created earlier, and then OK. This action creates an application setting for your account connection. This setting is used by the binding to connection to the database.
   Database name	Tasks	Name of the database that includes the collection to be monitored.
   Collection name	Items	Name of the collection to be monitored.
   Collection name for leases	leases	Name of the collection to store the leases.
   Create lease collection if it does not exist	Yes	Checks for existence of the lease collection and automatically creates it.

   Azure creates the Azure Cosmos DB triggered function based on the provided values.

4. To display the template-based function code, select Code + Test.

   

   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 Items container in the Tasks database.

Create the Items container

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.

   

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

4. Under SQL API, choose Tasks database and select New Container.

   

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

   

   Setting	Suggested value	Description
   Database ID	Tasks	The name for your new database. This must match the name defined in your function binding.
   Container ID	Items	The name for the new container. This must match the name defined in your function binding.
   Partition key	/category	A partition key that distributes data evenly to each partition. Selecting the correct partition key is important in creating a performant container.
   Throughput	400 RU	Use the default value. If you want to reduce latency, you can scale up the throughput later.

6. Click OK to create the Items container. It may take a short time for the container to get created.

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

Test the function

1. Expand the new Items container in Data Explorer, choose Items, then select New Item.

   

2. Replace the contents of the new item 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.

   

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 quickstarts in this collection build upon this quickstart. If you plan to work with subsequent quickstarts, tutorials, or with any of the services you've created in this quickstart, don't clean up the resources.

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

You've created resources to complete these quickstarts. You might 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.

   

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

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

3. Select Delete resource group and follow the instructions.

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

Now that you've created your first function, let's add an output binding to the function that writes a message to a Storage queue.