cloudwatch-line-notify-stack.ts

import * as cdk from 'aws-cdk-lib';
import { NodejsFunction } from 'aws-cdk-lib/aws-lambda-nodejs';
import * as lambda from 'aws-cdk-lib/aws-lambda';
import * as logs from 'aws-cdk-lib/aws-logs';
import * as destinations from 'aws-cdk-lib/aws-logs-destinations';
import { Construct } from 'constructs';

export class CloudwatchLineNotifyStack extends cdk.Stack {
  public readonly watchFn: lambda.Function;

  constructor(scope: Construct, id: string, props?: cdk.StackProps) {
    super(scope, id, props);

    const watchFn = new NodejsFunction(this, 'watchLambda', {
      entry: 'lambda/index.ts',
      handler: 'handler',
      runtime: lambda.Runtime.NODEJS_18_X,
    });
    
    //link an AWS CloudWatch log group for receiving logs
    const logGroup = logs.LogGroup.fromLogGroupArn(this, '<>', 
      '<>');

      // fields @timestamp, @message, @logStream, @log
      // | filter  ___
      // | sort @timestamp desc
      // | limit 20

      // | filter  (message == "Successfully produced a new block")
      // | filter  (level == "Error")


    new logs.SubscriptionFilter(this, 'WatchSubscription', {
      logGroup,
      destination: new destinations.LambdaDestination(watchFn),
      filterPattern: logs.FilterPattern.any(
        logs.FilterPattern.stringValue("$.message","=","Successfully produced a new block")
        // logs.FilterPattern.stringValue("$.level","=","Error")
      ),
      filterName: 'ProducedNewBlock',
    }); 
     
  }
}

cloudwatch-line-notify.ts

#!/usr/bin/env node
import 'source-map-support/register';
import * as cdk from 'aws-cdk-lib';
import { CloudwatchLineNotifyStack } from '../lib/cloudwatch-line-notify-stack';

const app = new cdk.App();
new CloudwatchLineNotifyStack(app, 'CloudwatchLineNotifyStack', {

  env: {
     account: '<AWS_ACCOUNT>', 
     region: '<AWS_REGION>' 
  },

});

index.ts

import { Callback, 
  CloudWatchLogsDecodedData, 
  CloudWatchLogsEvent, 
  CloudWatchLogsHandler, 
  Context, Handler } from 'aws-lambda';
import { Notify } from 'line-api'
import * as zlib from "zlib";

const notify = new Notify({
	token: "<LINE_NOTIFY_TOKEN>"
})

export const handler: CloudWatchLogsHandler = (
    event: CloudWatchLogsEvent,
    _context: Context,
    callback: Callback
  ): void => {
    console.log('EVENT: \n' + JSON.stringify(event, null, 2));
    
    const decoded = Buffer.from(event.awslogs.data, "base64");
    zlib.gunzip(decoded, (e, result) => {
        if (e) {
          callback(e, null);
        } else {
          const json: CloudWatchLogsDecodedData = JSON.parse(
            result.toString("ascii")
          );
          
          json.logEvents.forEach(async (event) => {
            const jsonlog = JSON.parse(event.message);
            console.log("DETAIL: (json log)", JSON.stringify(jsonlog, null, 2));
            
            // "metadata": {
            //     "breadcrumb": {
            //         "validated_transition": {
            //             "data": {
            //                 "protocol_state": {
            //                     "body": {
            //                         "consensus_state": {
        
            const consensus_state = jsonlog.metadata.breadcrumb.validated_transition.data.protocol_state.body.consensus_state
            const msg = `${jsonlog.message} - Block height: ${consensus_state.blockchain_length} Epoch: ${consensus_state.epoch_count}`;
            try {
                const resp = await notify.send({
                    message:  msg,
                 });
                console.log(resp);

            } catch (error) {
                console.log(error);

            }

          });

          callback(null);
        }
    });


};