Autoscaling and application load balancer - How to make them collaborate?

Question

I created a launch template, an autoscaling group and a target group all is running in 3 subnets, dualstack ipv4/ipv6 and load balancer is dual-stack-without-public-ip I can access my instance using http://[Ipv6] (the ipv6 of the instance, launched from autoscaling group), so, single instances are up and running and serving website well I am stuck at this point: I want load balancer to collaborate with autoscaling group to ... well .. to do load balancing ! ``` LoadBalancer: Type: AWS::ElasticLoadBalancingV2::LoadBalancer Properties: Name: LoadBalancer Scheme: internet-facing IpAddressType: dualstack-without-public-ipv4 Subnets: - !Ref PublicIpv6SubnetA - !Ref PublicIpv6SubnetB - !Ref PublicIpv6SubnetC SecurityGroups: - !Ref WebServerSecurityGroup # Usa il security group esistente LoadBalancerAttributes: - Key: idle_timeout.timeout_seconds Value: 60 Tags: - Key: Name Value: !Sub "${AWS::StackName}-Load-Balancer" InstanceLaunchTemplate: Type: AWS::EC2::LaunchTemplate Properties: LaunchTemplateName: InstanceLaunchTemplate LaunchTemplateData: ImageId: !Ref LatestAmiId InstanceType: t3.micro SecurityGroupIds: - !Ref WebServerSecurityGroup UserData: Fn::Base64: | #!/bin/bash yum install httpd -y service httpd start echo "

Hello from ipv6-only web server!

" > /var/www/html/index.html TagSpecifications: - ResourceType: "launch-template" Tags: - Key: Name Value: !Sub "${AWS::StackName}-Launch-Template" InstanceTargetGroup: Type: AWS::ElasticLoadBalancingV2::TargetGroup Properties: Name: TargetGroup Port: 80 # La porta su cui il target group ascolta il traffico Protocol: HTTP # Il protocollo utilizzato dal target group (HTTP, HTTPS, TCP, etc.) VpcId: !Ref VPC # ID della VPC in cui verrà creato il target group TargetType: instance HealthCheckEnabled: true # Abilita i controlli di integrità HealthCheckProtocol: HTTP # Protocollo utilizzato per i controlli di integrità HealthCheckPort: 80 # Porta su cui eseguire i controlli di integrità HealthCheckPath: / # Percorso per i controlli di integrità Matcher: # Configurazione del criterio di corrispondenza dei controlli di integrità HttpCode: 200 TargetGroupAttributes: # Attributi aggiuntivi del target group (opzionale) - Key: deregistration_delay.timeout_seconds Value: "30" # Timeout in secondi prima che una destinazione viene considerata non disponibile dopo una deregistrazione Tags: # Tags per identificare e organizzare il target group (opzionale) - Key: Name Value: !Sub "${AWS::StackName}-Target-Group" AutoScalingGroup: Type: AWS::AutoScaling::AutoScalingGroup Properties: AutoScalingGroupName: AutoScalingGroup LaunchTemplate: LaunchTemplateName: InstanceLaunchTemplate Version: !GetAtt InstanceLaunchTemplate.LatestVersionNumber MinSize: 1 # Numero minimo di istanze MaxSize: 3 # Numero massimo di istanze DesiredCapacity: 1 # Capacità iniziale VPCZoneIdentifier: - !Ref PublicIpv6SubnetA - !Ref PublicIpv6SubnetB - !Ref PublicIpv6SubnetC TargetGroupARNs: - !Ref InstanceTargetGroup # Riferimento al Target Group appena creato Tags: - Key: Name Value: !Sub "${AWS::StackName}-Auto-Scaling-Group" PropagateAtLaunch: true ``` What should I do to 'attach' the load balancer to my autoscale group? I think i am missing a piece of theory. How can AWS load balancing using my target group, where instances are created by AutoScalingGroup?

Answer

Hello.

"TargetGroupARNs" is specified in the AutoScaling settings, so when EC2 scales out, it will be linked to the specified target group.  
Also, it may not be included because it is not the full text of the CloudFormation template, but please create a listener using "AWS::ElasticLoadBalancingV2::Listener" to link the target group to the ALB.  
https://docs.aws.amazon.com/ja_jp/AWSCloudFormation/latest/UserGuide/aws-resource-elasticloadbalancingv2-listener.html

For example, to add a listener for port 80, you need to add the following template.  
```
  AlbListener:
    Type: AWS::ElasticLoadBalancingV2::Listener
    Properties:
      DefaultActions:
        - TargetGroupArn: !Ref InstanceTargetGroup
          Type: forward
      LoadBalancerArn: !Ref LoadBalancer
      Port: 80
      Protocol: HTTP
```

Answer

Hello,

You have almost completed the implementation to allow your Load Balancer to forward traffic across EC2 instances in the Auto Scaling group. However, you need to configure the Listeners in the Application Load Balancer (ALB). Listeners are essential as they enable the ALB to listen for incoming traffic and forward it to the target group. To read more about Listeners, https://docs.aws.amazon.com/elasticloadbalancing/latest/application/load-balancer-listeners.html

```
LoadBalancerListener:
    Type: AWS::ElasticLoadBalancingV2::Listener
    Properties:
      DefaultActions:
        - Type: forward
          TargetGroupArn: !Ref InstanceTargetGroup
      LoadBalancerArn: !Ref LoadBalancer
      Port: 80
      Protocol: HTTP
```

Answer

The key missing element is the Listener configuration for your Load Balancer.

For example:
```
  LoadBalancerListener:
    Type: AWS::ElasticLoadBalancingV2::Listener
    Properties:
      DefaultActions:
        - Type: forward
          TargetGroupArn: !Ref InstanceTargetGroup
      LoadBalancerArn: !Ref LoadBalancer
      Port: 80
      Protocol: HTTP
```

Autoscaling and application load balancer - How to make them collaborate?

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