Category: IT Essentials

1. Create a Topic on SNS

To set up Amazon SNS notifications

1. Open the Amazon SNS console at https://eu-central-1.console.aws.amazon.com/sns/v3/home
2. Choose Topics > Create topic
3. Create a topic with Name: CheckHealthW3Server and Display name: Health WWW servers. Other things should be default.
4. After that go to view detail of CheckHealthW3Server to create a subscription.

2. Create a subscription

We can ignore this step if we didn’t create a lambda function before.

1. Click Create subscription
2. Topic ARN: Enter a ARN of the CheckHealthW3Server topic.
3. Protocol: select AWS Lambda
4. Endpoint: An AWS Lambda function that can receive notifications from Amazon SNS
5. That’s all for a subscription. We can create many subscriptions with other protocol.

3. Create a channel and config to get message from lambda function

1. Slack > Create channel: #sns-notifications
2. Create a apps to post messages from external sources into Slack. Visit the link: https://channel.slack.com/apps and search app name: Incoming WebHooks
3. At homepage the app choose Add configuration and choose Post to Channel is #sns-notifications
4. After that you can get value for Webhook URL like that: https://hooks.slack.com/services/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

4. Create a lambda function to be trigger by SNS service

1. AWS Lambda > Create function
2. We have three ways to create a function lambda. But we should use a blueprint because it helps us to assign this function to the topic we want automatically. At search field we use the keyword is sns-message and choose language is Nodejs.
3. Fill these information for this function:
   1. Function name: notificationToSlack
   2. Execution role: Create a new role with basic Lambda permissions
   3. SNS topic: search CheckHealthW3Server
   4. Tick to Enable trigger
   5. Lambda function code: In this code you have to config again the path for calling webhook slack.

var https = require('https');
var util = require('util');

exports.handler = function(event, context) {
    console.log(JSON.stringify(event, null, 2));
    console.log('From SNS:', event.Records[0].Sns.Message);

    var postData = {
        "text": "*" + event.Records[0].Sns.Subject + "*"
    };

    var message = event.Records[0].Sns.Message;
    var severity = "danger";

    postData.attachments = [
        {
            "color": severity, 
            "text": message
        }
    ];

    var options = {
        method: 'POST',
        hostname: 'hooks.slack.com',
        port: 443,
        path: '/services/T2KFETZAQ/BH9KNUKU4/QOfFx4h08TF3D1OVKnhCmRS1'
    };

    var req = https.request(options, function(res) {
      res.setEncoding('utf8');
      res.on('data', function (chunk) {
        context.done(null);
      });
    });
    
    req.on('error', function(e) {
      console.log('problem with request: ' + e.message);
    });    

    req.write(util.format("%j", postData));
    req.end();
};

5. Publish a message to test

At the detail of the CheckHealthW3Server page.

1. Click on Publish message
2. Enter: Subject and Message body to send to the endpoint
3. Open the #sns-notifications channel to see the result.