Send a message from SNS to Slack using Lambda

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.

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