Exercise: Implementing Resilience in a TypeScript NestJS Application

Objectives

After completing this lesson, you will be able to:

  • Implementing resilience in a TypeScript NestJS application

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.

Prerequisites

For the complete execution of current exercise, you must execute the following activities first, using SAP Business Application Studio:

  1. Execute the following exercises:
    • Creating your free trial account in SAP BTP
    • Setting up the mock server, so that you have the Mock server program available in the cloud-s4-sdk-book folder.
  2. Run the following commands in a terminal, in case you didn't do it already in previous exercises, to clone the Git repository for the course:
    Code snippet
    cd ~/projects
    git clone https://github.com/SAP-samples/cloud-sdk-learning-journey.git
    Expand
  3. Choose FileOpen Folder and open the /home/user/projects/cloud-sdk-learning-journey/ folder.

Steps

  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.

      Code snippet
      cd ~/projects/cloud-sdk-learning-journey
      git checkout -f tsnestjs_v2.0_resilience
      Expand
  2. Build and run the project

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

      Code snippet
      cd cloudsdk_bp_ts
      npm i
      npm run start:dev
      Expand
  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:

      Code snippet
      cd ~/projects/cloud-s4-sdk-book
      npm run start
      Expand
  4. Query the Business Partner API of SAP S/4HANA Cloud

    1. Open the requests.http file in the cloudsdk_bp_ts folder

    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

    6. The request does not fail immediately. But will wait for the timeout period of 30 seconds. Start the Mock Server before 30 seconds

    7. Notice that the request instead of failing is able to recover and get the business partners now that the Mock Server was started within the timeout period of 30 seconds

  5. Optional: code walk-through.

    1. Review code in the following source files:

      File nameComments on code changes
      business-partner.service.ts

      Code logic is as follows...

      1. Import resilience from the @sap-cloud-sdk/resilience module
      2. 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.jsonNew SAP Cloud SDK modules have been installed for the project
      requests.httpProvides various HTTP requests that can be submitted to query the Business Partner API
      commands.txtProvides 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

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