Create a Python Application with Cloud Foundry Python Buildpack

First, you need to connect to the SAP BTP, Cloud Foundry environment with your enterprise (productive) subaccount. Your Cloud Foundry URL depends on the region where the API endpoint belongs to. To find out which one is yours, see: Regions and API Endpoints Available for the CF Environment

In this tutorial, we use eu20.hana.ondemand.com as an example.

1. Open a command-line console.

2. Set the Cloud Foundry API endpoint for your subaccount. Execute (using your actual region URL):

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   cf api https://api.cf.eu20.hana.ondemand.com
   

3. Log in to SAP BTP, Cloud Foundry environment:
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   cf login
   

4. When prompted, enter your user credentials – the email and password you have used to register your trial or productive SAP BTP account.

   IMPORTANT: If the authentication fails, even though you’ve entered correct credentials, try logging in via single sign-on.

5. Choose the org name and space where you want to create your application.

   If you’re using a trial account, you don’t need to choose anything. You can use only one org name, and your default space is dev.

RESULT

Details about your personal SAP BTP subaccount are displayed (API endpoint, user, organization, space).

You’re going to create a simple Python application.

1. In your local file system, create a new directory (folder). For example: python-tutorial

2. From your Visual Studio Code, open the python-tutorial folder.

3. In this folder, create a file manifest.yml with the following content:

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   ---
   applications:
   - name: myapp
     random-route: true
     path: ./
     memory: 128M
     buildpack: python_buildpack
     command: python server.py
   

   The manifest.yml file represents the configuration describing your application and how it will be deployed to Cloud Foundry.

   IMPORTANT: Make sure you don’t have another application with the name myapp in your space. If you do, use a different name and adjust the whole tutorial according to it.

4. Specify the Python runtime version that your application will run on. To do that, create a runtime.txt file with the following content:

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   python-3.11.1
   

5. This application will be a web server utilizing the Flask web framework. To specify Flask as an application dependency, create a requirements.txt file with the following content:

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   Flask==2.0.1
   

6. Create a server.py file with the following application logic:

   Python

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   import os
   from flask import Flask
   app = Flask(__name__)
   port = int(os.environ.get('PORT', 3000))
   @app.route('/')
   def hello():
       return "Hello World!"
   if __name__ == '__main__':
       app.run(host='0.0.0.0', port=port)
   

   This is a simple server, which will return a Hello World! message when requested.

7. Deploy the application on Cloud Foundry. To do that, in the python-tutorial directory, execute:

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   cf push
   

   Make sure you always execute cf push in the directory where the manifest.yml file is located! In this case, that’s python-tutorial.

8. When the staging and deployment steps are completed, the myapp application should be successfully started and its details displayed in the command console.

9. Open a browser window and enter the generated URL of the myapp application (see routes).

   For example: https://myapp-grouchy-rabbit.cfapps.eu20.hana.ondemand.com

RESULT

Your Python application is successfully deployed and running on the SAP BTP, Cloud Foundry environment. A Hello World! message is displayed in the browser.

You have created a service instance for SAP HANA Cloud (see Prerequisites at the beginning). Now you’re going to make a connection to your SAP HANA database from SAP HANA Schemas & HDI Containers - a service that runs on the SAP BTP, Cloud Foundry environment - and consume this service in your application.

1. Create a hana service instance named pyhana with service plan hdi-shared. Execute:

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   cf create-service hana hdi-shared pyhana
   

2. Bind this service instance to the application. Add pyhana in the manifest.yml file so that its content looks like this:

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   ---
   applications:
   - name: myapp
     random-route: true
     path: ./
     memory: 128M
     buildpack: python_buildpack
     command: python server.py
     services:
     - pyhana
   

3. To consume the service inside the application, you need to read the service settings and credentials from the application. To do that, use the cfenv Python module. Add two more lines to the requirements.txt file so that its content looks like this:

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   Flask==2.0.1
   cfenv==0.5.3
   hdbcli==2.9.23
   

4. Modify the server.py file to include additional lines of code - for reading the service information from the environment, and for executing a query with the hdbcli driver. After being requested, the application will now return a SAP HANA-related result. Replace the current content with the following:

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   import os
   from flask import Flask
   from cfenv import AppEnv
   from hdbcli import dbapi
   
   app = Flask(__name__)
   env = AppEnv()
   
   hana_service = 'hana'
   hana = env.get_service(label=hana_service)
   
   port = int(os.environ.get('PORT', 3000))
   @app.route('/')
   def hello():
       if hana is None:
           return "Can't connect to HANA service '{}' – check service name?".format(hana_service)
       else:
           conn = dbapi.connect(address=hana.credentials['host'],
                                port=int(hana.credentials['port']),
                                user=hana.credentials['user'],
                                password=hana.credentials['password'],
                                encrypt='true',
                                sslTrustStore=hana.credentials['certificate'])
   
           cursor = conn.cursor()
           cursor.execute("select CURRENT_UTCTIMESTAMP from DUMMY")
           ro = cursor.fetchone()
           cursor.close()
           conn.close()
   
           return "Current time is: " + str(ro["CURRENT_UTCTIMESTAMP"])
   
   if __name__ == '__main__':
       app.run(host='0.0.0.0', port=port)
   

5. In the python-tutorial directory, execute:

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   cf push
   

6. Refresh the URL of the myapp application (previously loaded in a browser window).

RESULT

The current SAP HANA time is displayed, in UTC time zone.

Authentication in the SAP BTP, Cloud Foundry environment is provided by the Authorization and Trust Management (XSUAA) service. In this example, OAuth 2.0 is used as the authentication mechanism. The simplest way to add authentication is to use the Node.js @sap/approuter package. To do that, a separate Node.js micro-service will be created, acting as an entry point for the application.

1. In the python-tutorial folder, create an xs-security.json file for your application with the following content:

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   {
     "xsappname" : "myapp",
     "tenant-mode" : "dedicated"
   }
   

   IMPORTANT: For trial accounts, enter the following additional oauth2-configuration code in your xs-security.json file:

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   {
     "xsappname" : "myapp",
     "tenant-mode" : "dedicated",
     "oauth2-configuration": {
       "redirect-uris": [
           "https://*.cfapps.eu20.hana.ondemand.com/**"
         ]
       }
   }
   

2. Create an xsuaa service instance named pyuaa with plan application, by executing the following command:

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   cf create-service xsuaa application pyuaa -c xs-security.json
   

3. Add the pyuaa service in manifest.yml so the file looks like this:

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   ---
   applications:
   - name: myapp
     random-route: true
     path: ./
     memory: 128M
     buildpack: python_buildpack
     command: python server.py
     services:
     - pyhana
     - pyuaa
   

   The pyuaa service instance will be bound to the myapp application during deployment.

4. To create a microservice (the application router), go to the python-tutorial folder and create a subfolder named web.

   IMPORTANT: Make sure you don’t have another application with the name web in your space! If you do, use a different name and adjust the rest of the tutorial according to it.

5. Inside the web folder, create a subfolder resources. This folder will provide the business application’s static resources.

6. Inside the resources folder, create an index.html file with the following content:

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   <html>
   <head>
   	<title>Python Tutorial</title>
   </head>
   <body>
     <h1>Python Tutorial</h1>
     <a href="/myapp/">My Python Application</a>
   </body>
   </html>
   

   This will be the myapp application start page.

7. In the web directory, execute:

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   npm init
   

   Press Enter on every step. This process will walk you through creating a package.json file in the web folder.

8. Now you need to create a directory web/node_modules/@sap and install an approuter package in it. To do that, in the web directory execute:

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   npm install @sap/approuter --save
   

9. In the web folder, open the package.json file and replace the scripts section with the following:

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   "scripts": {
         "start": "node node_modules/@sap/approuter/approuter.js"
   },
   

10. Now you need to add the web application to your project and bind the XSUAA service instance (pyuaa) to it. To do that, insert the following content at the end of your manifest.yml file.

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    - name: web
      random-route: true
      path: web
      memory: 128M
      env:
        destinations: >
          [
            {
              "name":"myapp",
              "url":"https://myapp-grouchy-rabbit.cfapps.eu20.hana.ondemand.com",
              "forwardAuthToken": true
            }
          ]
      services:
      - pyuaa
    

    For the url value, enter your generated URL for the myapp application.

11. In the web folder, create an xs-app.json file with the following content:

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    {
      "routes": [
        {
          "source": "^/myapp/(.*)$",
          "target": "$1",
          "destination": "myapp"
        }
      ]
    }
    

    With this configuration, the incoming request is forwarded to the myapp application, configured as a destination. By default, every route requires OAuth authentication, so the requests to this path will require an authenticated user.

12. Go to the python-tutorial directory and execute:

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    cf push
    

    This command will update the myapp application and deploy the web application.

    What’s going on?

    At this point of the tutorial, the URL of the web application will be requested instead of the myapp URL. It will then forward the requests to the myapp application.

13. When the staging and deployment steps are completed, the web application should be successfully started and its details displayed in the command console.

14. Open a new browser tab or window, and enter the generated URL of the web application.

    For example: https://web-unexpected-cheetah.cfapps.eu20.hana.ondemand.com

15. Enter the credentials for your SAP BTP user.

RESULT

• A simple application page with title Python Tutorial is displayed. When you click the My Application link, the current SAP HANA time is displayed, in UTC time zone.

• If you directly access the myapp URL, it displays the same result - the current SAP HANA time in UTC time zone.

Authorization in the SAP BTP, Cloud Foundry environment is also provided by the XSUAA service. In the previous example, the @sap/approuter package was added to provide a central entry point for the business application and to enable authentication. Now to extend the example, authorization will be added.

1. Add the sap-xssec security library to the requirements.txt file, to place restrictions on the content you serve. The file should look like this:

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   Flask==2.0.1
   cfenv==0.5.3
   hdbcli==2.9.23
   sap-xssec==3.0.0
   

2. Modify the server.py file to use the SAP xssec library. Replace the current content with the following:

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   import os
   from flask import Flask
   from cfenv import AppEnv
   from flask import request
   from flask import abort
   
   from sap import xssec
   
   from hdbcli import dbapi
   
   app = Flask(__name__)
   env = AppEnv()
   
   port = int(os.environ.get('PORT', 3000))
   hana = env.get_service(label='hana')
   uaa_service = env.get_service(name='pyuaa').credentials
   
   @app.route('/')
   def hello():
        if 'authorization' not in request.headers:
            abort(403)
        access_token = request.headers.get('authorization')[7:]
        security_context = xssec.create_security_context(access_token, uaa_service)
        isAuthorized = security_context.check_scope('openid')
        if not isAuthorized:
            abort(403)
   
        conn = dbapi.connect(address=hana.credentials['host'],
                              port=int(hana.credentials['port']),
                              user=hana.credentials['user'],
                              password=hana.credentials['password'],
                              encrypt='true',
                              sslTrustStore=hana.credentials['certificate'])
   
        cursor = conn.cursor()
        cursor.execute("select CURRENT_UTCTIMESTAMP from DUMMY")
        ro = cursor.fetchone()
        cursor.close()
        conn.close()
   
        return "Current time is: " + str(ro["CURRENT_UTCTIMESTAMP"])
   
   if __name__ == '__main__':
     app.run(host='0.0.0.0', port=port)
   

3. Go to the python-tutorial folder and execute:

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   cf push
   

   This command will update both myapp and web.

4. Try to access myapp again (in a browser) in both ways – directly, and through the web application router.

RESULT

Accessing the myapp application results in the following:

• If you try to access it directly, a 403 Forbidden response is displayed due to lack of permissions (lack of authorization header). This is a correct and expected behavior.

• If you try to access it through the web application router, the current SAP HANA time is displayed (in UTC time zone) – provided that you have the openid scope assigned to your user. Since the OAuth 2.0 client is used, the openid scope is assigned to your user by default, the correct authorization header is declared, and thus you are allowed to access the myapp application.

> In order for the new result to take effect immediately, you might need to clear the cache of your browser. Or just open the web application URL in a private/incognito browser tab.