Sync ECS task account with EC2 instances in AutoscalingGroup (AWS)

lambda.js

exports.handler = async (event, context, callback) => {
  
    console.log('Starting the process');
    var AWS = require('aws-sdk');

    // set the service names
    var ecsClusterName = "clustername";
    var ecsServiceName = "servicename";
    var autoScalingGroupName = "autoscalinggroupname";

    // determine the current desired count
    var ecs = new AWS.ECS({'region': 'eu-west-1'});
    var params = {cluster: ecsClusterName, services: [ecsServiceName]};
    
    // run autoscale
    ecs.describeServices(params, function(err, data) {
        if(!err) {            
             var currentInstances = data.services[0].desiredCount;
             if(currentInstances > 0) {
                // describe the autoscaling group, and scale up / in if there is a different service count
                var as = new AWS.AutoScaling({'region': 'eu-west-1'});    
                var params = {AutoScalingGroupNames: [autoScalingGroupName]};    
                as.describeAutoScalingGroups(params, function(err, data) {
                  if(!err) {
                    var instances = data.AutoScalingGroups[0].Instances;
                    var instancesInService = 0;
                    for(var i in instances) {
                      if(instances[i].LifecycleState == 'InService') {
                        instancesInService++;
                      }
                    }       
                    if(instancesInService == currentInstances) {
                        console.log('Current state is OK');
                    } else {
                        // scale up / down
                        var params = {
                          cluster: ecsClusterName,
                          service: ecsServiceName,
                          desiredCount: instancesInService
                        };
                        ecs.updateService(params, function(err, data) {
                          if (!err) {
                            console.log('Updated desired count to ' + instancesInService);
                          } else {
                            console.log(err);
                          }
                        });
                    }
                    var response = {
                        statusCode: 200,
                        body: JSON.stringify([])
                    };
                    context.succeed(response);
                  } else {
                    context.fail(err);
                  }
                });      
              }            
        } else {
          context.fail(err);
        }    
    });
};