Developing an Azure Functions trigger to process a change feed is an important skill for any professional planning to take the DP-420 Designing and Implementing Native Applications Using Microsoft Azure Cosmos DB exam. This kind of trigger proves quite useful for feeding changes in your Azure Cosmos DB into Azure Functions and having those changes processed in real-time.
Introduction to Azure Function with Cosmos DB Triggers
Azure Functions is a serverless computing service that allows users to run event-triggered code without having to provision or manage infrastructure explicitly. It integrates well with Cosmos DB through triggers that react to data changes in Azure Cosmos DB containers – whether those are inserts, replaces, deletes or raw changes made to the data.
Cosmos DB’s change feed is a persistent record of changes to a container in the order they occur. The change feed includes inserts and update operations made in each partition-key range within a container. This feature enables Azure Functions to react to changes, process them in the order they occur for each partition-key range, and update forms based on individual container changes.
Building an Azure Functions Trigger to Process a Change Feed
Step 1: Create an Azure Cosmos DB account, database, and container
Begin by setting up your Azure Cosmos DB. If you don’t have one already, you can create one using the Azure portal, Azure CLI, or ARM templates. Since Azure Functions uses SQL API to connect with Azure Cosmos DB, ensure that you create a SQL API account.
Step 2: Creating an Azure Function App
Next, create an Azure Function app in your preferred development environment. If you use the Azure portal, navigate to the “Functions” area, click “Create,” and fill in the necessary details.
Step 3: Setting up the Cosmos DB Trigger
Now it’s time to set up your Cosmos DB trigger on your Azure Function. You do this by creating a function in your Function App and choosing Azure Cosmos DB for your trigger. You’ll also need to specify the following parameters:
- Connection String Setting: This is the name of the app setting containing your Cosmos DB connection string.
- Database Name: The name of your Cosmos DB database.
- Collection Name: This is the name of the collection in your Cosmos DB from which the trigger pulls changes.
- Create Lease Collection If Not Exists: This indicates whether the trigger should create a lease collection if one doesn’t exist.
Step 4: Coding the Function
The last step is to code your Azure Function with a trigger to process the Cosmos DB change feed. Your function code would be something like this:
def main(documents: func.DocumentList):
if documents:
logging.info('- - - - - New Change Feed - - - - -')
for doc in documents:
logging.info('Document Id: %s', doc['id'])
Conclusion
Understanding how to develop an Azure Functions trigger to process a change feed is a critical part of designing and implementing native applications using Microsoft Azure Cosmos DB. This knowledge will not only help during the DP-420 exam but also make you quite proficient in creating efficient, real-time applications using Azure Cosmos DB and Azure Functions.
Practice Test
True or False: Azure Functions is a serverless compute service that allows you to run code for responding to changes in data or reacting to events.
• True
• False
Answer: True.
Explanation: Azure Functions is a serverless computation service that executes your code based on certain triggers such as HTTP requests, Azure Cosmos DB data changes, etc.
What is the Azure Function trigger for processing change feeds in Azure Cosmos DB?
• A. Event Hub trigger
• B. Queue trigger
• C. CosmosDB trigger
• D. Blob trigger
Answer: C. CosmosDB trigger
Explanation: Azure Functions provides a CosmosDB trigger that responds whenever there are changes in an Azure Cosmos DB container.
True or False: Azure Functions triggered by Azure Cosmos DB change feed can only be written in JavaScript.
• True
• False
Answer: False.
Explanation: Azure Functions supports various programming languages such as C#, Java, Python, JavaScript, etc.
What is the Change Feed in Azure Cosmos DB?
• A. A list of all items in the database.
• B. A list of all changes that have occurred in the database.
• C. A list of all the collections in the database.
• D. A list of all the deleted items in the database.
Answer: B. A list of all changes that have occurred in the database.
Explanation: Change Feed in Azure Cosmos DB is a mechanism that ensures ordered, durable, and reliable delivery of every update made to an item in any container in the database.
Which of the following services can Azure Cosmos DB Change Feed be integrated with to process the feed data?
• A. Azure Functions
• B. Azure Logic Apps
• C. Azure Stream Analytics
• D. All of the above
Answer: D. All of the above
Explanation: Azure Cosmos DB change feed can be integrated with Azure Functions, Azure Logic Apps, and Azure Stream Analytics to process the feed data.
True or False: It is not possible to use Azure Functions and Azure Cosmos DB together to build event-driven applications.
• True
• False
Answer: False.
Explanation: Azure Functions can be triggered by Azure Cosmos DB change feed, which enables the development of event-driven applications.
What kind of data does the Azure Cosmos DB Change Feed contain?
• A. All data in the database.
• B. Only new and updated data.
• C. Only deleted data.
• D. Both new and deleted data.
Answer: B. Only new and updated data.
Explanation: The Change Feed in Azure Cosmos DB contains a log of all the newly inserted or updated items in the DB.
True or False: Change feed support in Azure Cosmos DB works by listening to an Azure Cosmos DB container for any changes.
• True
• False
Answer: True.
Explanation: Change feed in Azure Cosmos DB works by listening to an Azure Cosmos DB container for any changes. It then outputs the sorted list of documents that were changed, in the order in which they were modified.
Does Azure Functions allow you to choose the number of instances of a function to run when a new batch of events comes in?
• A. Yes
• B. No
Answer: A. Yes
Explanation: Azure Functions provides a wide range of options to choose from when it comes to running a function, including dynamic scaling based on the number of events.
True or False: The change feed support in Azure Cosmos DB is not key to building efficient and scalable solutions.
• True
• False
Answer: False.
Explanation: Change Feed support in Azure Cosmos DB enables building efficient and scalable event-driven applications, hence it is a key component.
Interview Questions
What is Azure Function?
Azure Functions is a serverless compute service that lets you run event-triggered code without having to explicitly provision or manage infrastructure.
What is a Change Feed in Azure Cosmos DB?
Change Feed in Azure Cosmos DB allows clients to keep up with changes in data within a container. The change feed includes inserts and update operations made on documents within the container.
How does Azure Functions trigger work with Azure Cosmos DB’s change feed?
An Azure Functions trigger can be developed to read from Azure Cosmos DB’s Change Feed. As new records are added or changes are made to existing records, they can be read by the Azure Function to initiate the processing.
What is the benefit of using Azure Functions with Change Feed?
Azure Functions with Change Feed can be used to create a real-time, serverless, and event-driven architecture. This allows your applications to respond immediately to the changes in data in your Cosmos DB.
What do you need to specify to set up a Trigger function using Azure Functions?
To set up a Trigger function, you generally need to specify the type of triggers (in this case Cosmos DB Change feed), the connection string for the Cosmos DB account, and the name of the Cosmos DB container you want to monitor.
What is the Azure Function binding for Cosmos DB Change Feed?
The binding is CosmosDBTrigger.
In which programming languages can Azure Functions be written?
Azure Functions can be written in multiple languages such as C#, F#, Node.js, Python, PHP, batch, bash, Java, or any executable.
Can Azure Functions work with both SQL (Core) API and MongoDB API in Cosmos DB?
Yes, Azure Functions can work with both SQL (Core) API and MongoDB API in Cosmos DB, the Change Feed feature is available in both APIs.
Can you use Change Feed to track deletes in Cosmos DB?
While Change Feed can track additions and updates, it currently does not track deletion of documents.
Is the data returned by the Change Feed sorted in a particular order?
Yes, the data returned by the Change Feed is sorted by the order in which they were modified, in ascending order.
Does developing an Azure Functions trigger to process a change feed requires an Azure Functions premium plan?
No, it does not require a premium plan. You can accomplish this with the consumption plan.
Can a single Azure Function be triggered from multiple containers’ Change Feed in Cosmos DB?
No, Azure Functions is designed to work with a single container’s Change Feed. To process changes from multiple containers, you would need to develop multiple Azure Functions.
What lease container is needed in the CosmosDBTrigger to use the Change Feed functionality?
The lease container is used to store the checkpoint or state for your Azure Function trigger working with Change Feed. This allows the Azure Function to know where to continue reading changes after a failure or shutdown.
What happens if the Azure Function fails to process some changes from the Change Feed?
If an Azure Function fails to process some changes from the Change Feed, it retains its state in the lease container and can retry the processing from where it left.
Can the Change Feed in Azure Cosmos DB be paused?
The Change Feed itself cannot be paused, but you can control the processing of the Change Feed in your Azure Function by managing the status of the Function.
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