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Create an Application for Producing Messages

Requires Customer/Partner License
Develop and deploy a basic Node.js-based messaging application for sending messages to an SAP Event Mesh Queue.
You will learn
  • How to create a basic messaging client application for sending messages to a queue
  • How to deploy this application to the SAP Business Technology Platform and test it
pradeeppanda-sapPRADEEP PANDAMarch 4, 2022
Created by
pradeeppanda-sap
November 12, 2019
Contributors
pradeeppanda-sap
  • Step 1
    1. Install Node.js and configure it locally.

    2. Add the dependency in applications package.json and run npm for it:

      npm install

    3. Create a directory that holds the files for your application - name it for example Producer. Into this directory we will create three files:

      • The manifest.yml is the deployment descriptor and contains all required information to deploy an application to a SAP Business Technology Platform Cloud Foundry instance.

      • The package.json specifies the version of a package that your app depends on.

      • The application file obviously holds the executable code.

    Now create these files following the descriptions below into the created directory.

  • Step 2

    Use the following code to create a manifest.yml file that binds your application to the messaging service.

    You need to add domain, messaging service and your queue name in the indicated spaces.

    YAML
    Copy
    applications:
      - name: producer
        host: producer-host
        buildpack: 'https://github.com/cloudfoundry/nodejs-buildpack'
        memory: 256M
        health-check-type: none
        path: .
        command: node producer.js
        services:
          - <REPLACE WITH YOUR MESSAGING SERVICE>
        env:
          SAP_JWT_TRUST_ACL: '[{"clientid":"*","identityzone":"*"}]'
          SAP_XBEM_BINDINGS: |
            {
              "inputs": {},
              "outputs": {
                "myOutA" : {
                  "service": "<REPLACE WITH YOUR MESSAGING SERVICE>",
                  "address": "topic:<REPLACE WITH YOUR TOPIC>",
                  "reliable": false
                },
                "myOutB" : {
                  "service": "<REPLACE WITH YOUR MESSAGING SERVICE>",
                  "address": "topic:<REPLACE WITH YOUR TOPIC>",
                  "reliable": false
                }
              }
            }
    
    
  • Step 3

    Create a package.json file to list the packages your project depends on and to specify versions of a package that your project can use. This makes your build reproducible, and therefore easier to share with other developers.

    JSON
    Copy
    {
            "name": "producer",
            "description": "Simple NodeJS Application producing messages",
            "version": "0.0.1",
            "engines": {
                    "node": ">=6.9.1"
            },
                  "dependencies": {
            "@sap/xb-msg": "^0.9.12",
            "@sap/xb-msg-amqp-v100": "^0.9.48",
            "@sap/xb-msg-env": "^0.9.7",
            "@sap/xsenv": "^3.1.0"
            },
            "scripts": {
                    "start": "node producer.js"
            }
    }
    
  • Step 4

    Use the following code to create a producer.js file. This file holds the actual application. Find descriptions of what it does as comments in the coding.

    On a higher level you do the following:

    1. Perform settings in respect to Node.js modules and to messaging.

    2. Get the messaging options from the environment.

    3. The messaging client is instantiated using the options.

    4. Client and stream handler methods are defined.

    As a result, the application sends messages to the defined topic and writes a quick info including a counter into the log file.

    JavaScript
    Copy
    "use strict";
    
    //------------------------------------------------------------------------------------------------------------------
    //  Basic setup in respect to modules, messaging settings and getting messaging options
    //------------------------------------------------------------------------------------------------------------------
    
    const msg = require('@sap/xb-msg');
    const env = require('@sap/xb-msg-env');
    const xsenv = require('@sap/xsenv');
    const service = '<REPLACE WITH YOUR MESSAGING SERVICE>';
    const taskList = {
        myOutA : { topic: '<REPLACE WITH YOUR TOPIC>' , timerMin: 1, timerMax: 11 },
        myOutB : { topic: '<REPLACE WITH YOUR TOPIC>' , timerMin: 5, timerMax:  8 }
    };
    var counter = 1;
    
    xsenv.loadEnv();
    
    //------------------------------------------------------------------------------------------------------------------
    // Start messaging client
    //------------------------------------------------------------------------------------------------------------------
    
    const client = new msg.Client(env.msgClientOptions(service, [], ['myOutA', 'myOutB']));
    
    
    function getRandomInt(min, max) {
        min = Math.ceil(min);
        max = Math.floor(max);
        return (Math.floor(Math.random() * (max - min + 1)) + min) * 1000;
    }
    
    function initTasks(tasks, client) {
        Object.getOwnPropertyNames(tasks).forEach((id) => {
            const task = tasks[id];
            const stream = client.ostream(id);
    
            const handler = () => {
                console.log('publishing message number ' + counter + ' to topic ' + task.topic);
    
                const message = {
                    payload: Buffer.from("Message Number " + counter)
    
                };
                if (!stream.write(message)) {
                    console.log('wait');
                    return;
                }
                setTimeout(handler, getRandomInt(task.timerMin, task.timerMax));
                counter++;
            };
    
            stream.on('drain', () => {
                setTimeout(handler, getRandomInt(task.timerMin, task.timerMax));
            });
    
            setTimeout(handler, getRandomInt(task.timerMin, task.timerMax));
        });
    }
    
    //------------------------------------------------------------------------------------------------------------------
    // Messaging client handler methods
    //------------------------------------------------------------------------------------------------------------------
    
    client
        .on('connected', () => {
            console.log('connected');
            initTasks(taskList, client);
        })
        .on('drain', () => {
            console.log('continue');
        })
        .on('error', (error) => {
            console.log(error);
        });
    
    client.connect();
    
  • Step 5
    1. Go to <filepath directory to manifest.yml> and enter npm install to download potentially missing Node.js modules.

    2. To deploy the producing application to your Cloud Foundry space enter cf push.

    Your application gets deployed to the cloud and is started.

  • Step 6

    Once the application is started up, you can test your message producer. There are several options for this:

    • If you already have the consumer app deployed and started you should be able to see the messages sent by the consumer app in the logs. Use cf logs producer or cf logs producer --recent to see the logs.

    • If you stop the consuming application or have not deployed it yet the count for the messages in the queue that can be found in the messaging cockpit goes up.

    • Alternatively you could use Postman to consume the messages.

    Which three files do you have to create for your Producer application?

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