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Thanks for your time in advance. I am pretty new to AWS and trying to setup a cloud facing application processing HTTP / HTTPS requests.

I have a domain-name (example.com) attached to the Elastic Load Balancer (ELB) and my requirement is just to have a ELB attached to a AutoScaling group (ASG) which would have a min-max of 2-5 EC2s. Preferably I would want to place my EC2s created by ASG to be placed in a private subnet.

I was following the solution provided here, but as I understand in step 5, it is for connecting the ELB to existing EC2 instances. But my requirement is to attach it to a ASG and hence cannot connect to specific EC2 instances.

I am focusing on just two AZ for now and created a public and private subnet each in both the AZ. After creating the ELB and attaching it to two public subnets, I proceeded for Launch-Configuration & ASG. I would request some clarification on the implication of the following selections while setting up the LC and ASG.

While creating a Launch Configuration for an ASG, in one of the steps (IP Address Type) I have three options, namely:

(1) Give Public IP to new instances if created in default VPC/SubNet

(2) Always Public IP for new instances

(3) No Public IP for new instances.

Which one of the above should be selected given my requirement?

Additional Questions

  1. When selecting the subnets while creating ASG, should I select both public and private subnets or only public SN or only Private SN ? My guess was Private subnet only as I wanted to place the EC2 in private SN.

  2. If the EC2s created by the ASG will be deployed in Private SN, what else should be present in the public subnet?

Thanks again for your time and guidance.

Update on 6/13

For the questions I had posted above, I went ahead with choices as below:

  1. While creating a Launch Configuration for an ASG, IP Address Type : No Public IP for new instances.

  2. When selecting the subnets while creating ASG : Only Private SN

  3. I placed a NAT Gateway in the public subnet and updated the routing table of Private Subnet to include a route for 0.0.0.0/0 to NAT

Things are working now !!

Sujith
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1 Answers1

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You can find the AWS document on attaching to an autoscaling group here. You attach the ELB to the ASG, or if its an application load balancer you attach the target group for your ALB to the ASG:

To attach a load balancer to a group

  • Open the Amazon EC2 console at https://console.aws.amazon.com/ec2/.

  • On the navigation pane, under Auto Scaling, choose Auto Scaling Groups.

  • Select your group.

  • On the Details tab, choose Edit.

Do one of the following:

  • [Classic Load Balancers] For Load Balancers, select your load balancer.

  • [Target groups] For Target Groups, select your target group.

  • Choose Save.

You do no need public IP addresses if your instances will be behind an ELB. You should also launch them in a private subnet. Your ELB will be in public subnets and relay communications to your instances in those private subnets. The ELB will also be assigned a DNS name you alias to a custom DNS name of your own.

From the docs above, you can also attach and detach using the CLI:

To attach a Classic Load Balancer

Use the following attach-load-balancers command to attach the specified load balancer to your Auto Scaling group:

aws autoscaling attach-load-balancers --auto-scaling-group-name my-asg --load-balancer-names my-lb

To attach to a target group

Use the following attach-load-balancer-target-groups command to attach the specified target group to your Auto Scaling group:

aws autoscaling attach-load-balancer-target-groups --auto-scaling-group-name my-asg --target-group-arns my-targetgroup-arn

To detach a Classic Load Balancer

Use the following detach-load-balancers command to detach a load balancer from your Auto Scaling group if you no longer need it:

aws autoscaling detach-load-balancers --auto-scaling-group-name my-asg --load-balancer-names my-lb

To detach a target group

Use the following detach-load-balancer-target-groups command to detach a target group from your Auto Scaling group if you no longer need it:

aws autoscaling detach-load-balancer-target-groups --auto-scaling-group-name my-asg --target-group-arns my-targetgroup-arn
Brandon Miller
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  • Hello @Brandon, Thanks for your response. Sorry if my question was not clear enough. I am good with the steps of attaching the ASG to ELB. My confusion was more related to selecting the IP Type while configuring LC and selecting subnets for the ASG. As mentioned in the update provided above, I went ahead and completed the setup. But the Private IP instances in Private subnet were not reachable even when ELB was in public SN. Then I added the NAT gateway in one of the public subnet and updated the routing table of Private Subnet to include a route for 0.0.0.0/0 to NAT. **SUCCESS** – Sujith Jun 13 '18 at 14:01