Simplistic lambda function for autoscaling the number of tasks in an ECS service

autoscale-ecs-tasks-lambda.js

var aws = require('aws-sdk');
 
exports.handler = function(event, context) {
  var ecsRegion = 'us-east-1';
  
  // Safegaurd against out of control service scaling
  var maxCount = {
    deathstar: 6
  };
  
  var message = JSON.parse(event.Records[0].Sns.Message);
  var serviceName;
  var clusterName;
 
  for (var dimension in message.Trigger.Dimensions) {
    if (message.Trigger.Dimensions[dimension].name == 'ServiceName') {
      serviceName = message.Trigger.Dimensions[dimension].value;
    }
    if (message.Trigger.Dimensions[dimension].name == 'ClusterName'){
      clusterName = message.Trigger.Dimensions[dimension].value;
    }
  } 
  
  console.log('The service that triggered this alarm was: ' + serviceName);
  console.log('The cluster that triggered this alarm was: ' + clusterName);
  
  var ecs = new aws.ECS({region: ecsRegion});
  ecs.describeServices({services:[serviceName], cluster: clusterName}, function(err, data) {
    console.log('Finished describing service to fetch current task count');
    if (err) {
      console.log(err, err.stack);
    } else {
      var desiredCount = data.services[0].desiredCount;
      if (desiredCount < maxCount[serviceName]) {
        desiredCount++;
    
        var params = {
          service: serviceName,
          desiredCount: desiredCount,
          cluster: clusterName
        };
    
        ecs.updateService(params, function(err, data) {
          console.log('Finished updating service task count');
          if (err) {
            console.log(err, err.stack);
          } else {
            console.log(data);
            context.succeed();
          }
        });
      } else {
        console.log('Service count for ' + serviceName + ' is already max on ' + clusterName);
        context.fail();
      }
    }
  });
};