Exercise: Implementing Resilience in a TypeScript NestJS Application

In this exercise, you will learn how to implement resilience in SAP Cloud SDK application. We will use the Mock Server instead of the actual SAP S/4HANA Cloud.

1. Checkout the branch tsnestjs_v2.0_resilience in SAP Business Application Studio

   1. Open SAP Business Application Studio.

   2. Run the following commands in the terminal.

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      cd ~/projects/cloud-sdk-learning-journey
      git checkout -f tsnestjs_v2.0_resilience

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2. Build and run the project

   1. Run the application by executing the following commands in the terminal

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      cd cloudsdk_bp_ts
      npm i
      npm run start:dev

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3. Make sure that the Mock Server is up and running as described in the related previous exercise.

   1. In case the Mock server is installed but not started, you need to open a new terminal window and run the following commands:

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      cd ~/projects/cloud-s4-sdk-book
      npm run start

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4. Query the Business Partner API of SAP S/4HANA Cloud

   1. Open the requests.http file

   2. Click on Send Request in the requests.http file to submit the GET request for business partners

   3. Verify that the list of business partners are returned from the Mock Server. Note: If the Mock Server is not running, make sure to run the Mock Server on port 8081 by following the prerequisites at the top

      

   4. Stop the Mock Server by pressing Ctrl + C in the Mock Server project terminal

   5. Click on Send Request in the requests.http file to submit the GET request for business partners within 30 seconds.

   6. Verify that the list of business partners are returned from the cache, since the Mock Server is not running

      

   7. Click on Send Request in the requests.http file to submit the GET request for business partners after 30 seconds. The Business Partners are not returned anymore.

   8. Re-start the mock server and re-run the query to make sure it works again.

   9. Stop the running application using Ctrl + C in the corresponding terminal window.

5. Optional: code walk-through.

   1. Review code in the following source files:

      File name	Comments on code changes
      business-partner.service.ts	Code logic is as follows... Import resilience from the @sap-cloud-sdk/resilience module Use the middleware function to build a resilience middleware. In our example, we will use the following values timeout: 30 seconds circuitBreaker: true retry: true
      package.json	New SAP Cloud SDK modules have been installed for the project
      requests.http	Provides various HTTP requests that can be submitted to query the Business Partner API
      commands.txt	Provides various commands that can be run on the terminal

      Note

      Check out the SAP Cloud SDK documentation on Executing an OData GET request using SAP Cloud SDK for JavaScript. https://sap.github.io/cloud-sdk/docs/js/tutorials/getting-started/execute-an-odata-request

6. Optional: Manually modify the project in ~/projects/cloudsdk_bp_tsto use resilience.

   1. Open the projects/cloudsdk_bp_ts folder in the workspace, by choosing File → Open Folder....

   2. Create or update the following files in the table below

      File name	Type	Contents
      business-partner.service.ts Path: src/business-partner	Modified	Copy contents from here...

      

   3. Build and run the project in projects/cloudsdk_bp_ts:

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      cd ~/projects/cloudsdk_bp_ts
      npm i
      npm run start:dev

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   4. Stop the running application using Ctrl + C in the corresponding terminal window.