SNS Slack Alerts

SNS Slack Alerts is brought to you by your friends at Last Call Media, this repository contains two NPM packages for dealing with publishing Slack alerts in Lambda. We believe that AWS infrastructure alerts should be routed through SNS for two reasons:

1. To keep Slack credentials from being exposed throughout your infrastructure.
2. To allow publishing from places other than NodeJS code (eg: Cloudwatch alarms).
3. To allow routing of alerts to additional SNS targets (eg: e-mail, or a central alert collection system).

There are two components to this architecture:

• Publisher - An NPM package allowing you to easily publish an SNS message that is well-formatted for Slack, and understandable on other mediums. The publisher is usable from any Node application (Lambda or traditional) that has IAM permissions to publish to an SNS topic.
• Consumer - An NPM package for use in a Lambda that receives the SNS notification and routes it to Slack.

The minimal setup for using this system would be two Lambdas - one running code that would generate an alert (the "publisher"), and one running code that would consume the alert (the consumer).

In this scenario, the "publisher" is any javascript that wants to publish Slack alerts, but we'll assume it's a Lambda:

/**
 * This is the "publisher."
 *
 * Really, this would be any code running on your infrastructure that needs to trigger alerts.
 */
const AlertFactory = require('@lastcall/sns-slack-alerts-publisher');
const {ALERT_TOPIC_ARN} = process.env;

const alerter = new AlertFactory(ALERT_TOPIC_ARN, 'My awesome service/dev');

exports.handler = async function(event, context) {
    try {
        somethingDangerous();
    }
    catch(err) {
        console.log(err.message);
        const message = alerter.create('Something bad happened', err.message);
        await message.publish();
    }
}

One thing to note is that this Lambda will need to have a role that gives it SNS:Publish permissions on the SNS topic.

Next, we'd have a Lambda wired up to accept the alert that gets published to the topic:

const {SNSSlackPublisher} = require('@lastcall/sns-slack-alerts-consumer');
const {SLACK_TOKEN, CHANNEL} = process.env;

// Slack message settings for topics that don't have a special setting:
const defaultMessage = {
    as_user: true,
    channel: CHANNEL
}
// Optional: Map of special topics to slack message bodies:
const topicMap = {
    // Override the message for this specific topic so it
    // appears to come from Yoda.
    'arn:aws:sns:us-east-1:000000000:special-alerts': {
        username: 'Yoda',
        icon_emoji: ':yoda:',
        as_user: false,
        channel: CHANNEL,
    }
}

const publisher = new SNSSlackPublisher(SLACK_TOKEN, defaultMessage, topicMap);

exports.handler = async function(data, context, callback) {
    const messages = data.Records.map(record => {
        return publisher.publish(record);
    })
    return Promise.all(messages)
}