Azure Cosmos DB: Build a Flask app with the MongoDB API

Azure Cosmos DB is Microsoft’s globally distributed multi-model database service. You can quickly create and query document, key/value, and graph databases, all of which benefit from the global distribution and horizontal scale capabilities at the core of Azure Cosmos DB.

This quick start guide, uses the following Flask example and demonstrates how to build a simple To-Do Flask app with the Azure Cosmos DB Emulator and the Azure Cosmos DB MongoDB API instead of MongoDB.

Prerequisites

  • Download the Azure Cosmos DB Emulator. The emulator is currently only supported on Windows. The sample shows how to use the sample with a production key from Azure, which can be done on any platform.

  • If you don’t already have Visual Studio Code installed, you can quickly install VS Code for your platform (Windows, Mac, Linux).

  • Be sure to add Python Language support by installing one of the popular Python extensions.

    1. Select an extension.
    2. Install the extension by typing ext install into the Command Palette Ctrl+Shift+P.

      The examples in this document use Don Jayamanne's popular and full featured Python Extension.

Clone the sample application

Now let's clone a Flask-MongoDB API app from github, set the connection string, and run it. You see how easy it is to work with data programmatically.

  1. Open a command prompt, create a new folder named git-samples, then close the command prompt.

    md "C:\git-samples"
    
  2. Open a git terminal window, such as git bash, and use the cd command to change to the new folder to install the sample app.

    cd "C:\git-samples"
    
  3. Run the following command to clone the sample repository. This command creates a copy of the sample app on your computer.

    git clone https://github.com/Azure-Samples/CosmosDB-Flask-Mongo-Sample.git
    
  4. Run the following command to install the python modules.

    pip install -r .\requirements.txt
    
  5. Open the folder in Visual Studio Code.

Review the code

This step is optional. If you're interested in learning how the database resources are created in the code, you can review the following snippets. Otherwise, you can skip ahead to Run the web app.

The following snippets are all taken from the app.py file and uses the connection string for the local Azure Cosmos DB Emulator. The password needs to be split up as seen below to accommodate for the forward slashes that cannot be parsed otherwise.

  • Initialize the MongoDB client, retrieve the database, and authenticate.

    client = MongoClient("mongodb://127.0.0.1:10250/?ssl=true") #host uri
    db = client.test    #Select the database
    db.authenticate(name="localhost",password='C2y6yDjf5' + r'/R' + '+ob0N8A7Cgv30VRDJIWEHLM+4QDU5DE2nQ9nDuVTqobD4b8mGGyPMbIZnqyMsEcaGQy67XIw' + r'/Jw==')
    
  • Retrieve the collection or create it if it does not already exist.

    todos = db.todo #Select the collection
    
  • Create the app

    app = Flask(__name__)
    title = "TODO with Flask"
    heading = "ToDo Reminder"
    

Run the web app

  1. Make sure the Azure Cosmos DB Emulator is running.

  2. Open a terminal window and cd to the directory that the app is saved in.

  3. Then set the environment variable for the Flask app with set FLASK_APP=app.py or export FLASK_APP=app.py if you are using a Mac.

  4. Run the app with flask run and browse to http://127.0.0.1:5000/.

  5. Add and remove tasks and see them added and changed in the collection.

Create a database account

  1. In a new window, sign in to the Azure portal.
  2. In the left menu, click Create a resource, click Databases, and then under Azure Cosmos DB, click Create.

    Screen shot of the Azure portal, highlighting More Services, and Azure Cosmos DB

  3. In the New account blade, specify MongoDB as the API and fill out your desired configuration for the Azure Cosmos DB account.

    • ID must be a unique name you wish to use to identify your Azure Cosmos DB account. It may only contain lower case letters, numbers, the '-' character, and must be between 3 and 50 characters.
    • Subscription is your Azure subscription. It will be filled out for you.
    • Resource Group is the resource group name for your Azure Cosmos DB account. Select Create New, then enter a new resource-group name for your account. For simplicity, you can use the same name as your ID.
    • Location is the geographic location where your Azure Cosmos DB instance is located. Choose the location closest to your users.

      Then click Create.

      The new account page for Azure Cosmos DB

  4. The account creation takes a few minutes. Wait for the portal to display the Congratulations! Your Azure Cosmos DB account with MongoDB API is ready page.

    The Azure portal Notifications pane

Update your connection string

If you want to test the code against a live Azure Cosmos DB Account, go to the Azure portal to create an account and get your connection string information. Then copy it into the app.

  1. In the Azure portal, in your Azure Cosmos DB account, in the left navigation click Connection String, and then click Read-write Keys. You'll use the copy buttons on the right side of the screen to copy the Username, Password, and Host into the Dal.cs file in the next step.

  2. Open the app.py file in the root directory.

  3. Copy your username value from the portal (using the copy button) and make it the value of the name in your app.py file.

  4. Then copy your connection string value from the portal and make it the value of the MongoClient in your app.py file.

  5. Finally copy your password value from the portal and make it the value of the password in your app.py file.

You've now updated your app with all the info it needs to communicate with Azure Cosmos DB. You can run it the same way as before.

Deploy to Azure

To deploy this app, you can create a new web app in Azure and enable continuous deployment with a fork of this github repo. Follow this tutorial to set up continuous deployment with Github in Azure.

When deploying to Azure, you should remove your application keys and make sure the section below is not commented out:

    client = MongoClient(os.getenv("MONGOURL"))
    db = client.test    #Select the database
    db.authenticate(name=os.getenv("MONGO_USERNAME"),password=os.getenv("MONGO_PASSWORD"))

You then need to add your MONGOURL, MONGO_PASSWORD, and MONGO_USERNAME to the application settings. You can follow this tutorial to learn more about Application Settings in Azure Web Apps.

If you don't want to create a fork of this repo, you can also click the deploy to Azure button below. You should then go into Azure and set up the application settings with your Cosmos DB account info.

Note

If you plan to store your code in Github or other source control options, please be sure to remove your connection strings from the code. They can be set with application settings for the web app instead.

Review SLAs in the Azure portal

The throughput, storage, availability, latency, and consistency of the resources in your account are monitored in the Azure portal. Let's take a quick look at these metrics.

  1. Click Metrics in the navigation menu.

    Metrics in the Azure portal

  2. Click through each of the tabs so you're aware of the metrics Azure Cosmos DB provides.

    Each chart that's associated with the Azure Cosmos DB Service Level Agreements (SLAs) provides a line that shows if any of the SLAs have been violated. Azure Cosmos DB makes monitoring your SLAs transparent with this suite of metrics.

    Azure Cosmos DB metrics suite

Clean up resources

If you're not going to continue to use this app, delete all resources created by this quickstart with the following steps so you don't incur any charges:

  1. In the Azure portal, select Resource groups on the far left, and then select the resource group you created.

    If the left menu is collapsed, click Expand button to expand it.

    Metrics in the Azure portal

  2. In the new window select the resource group, and then click Delete resource group.

    Metrics in the Azure portal

  3. In the new window, type the name of the resource group to delete, and then click Delete.

Next steps

In this quickstart, you've learned how to create an Azure Cosmos DB account and run a Flask app using the API for MongoDB.You can now import additional data to your Cosmos DB account.