CODEWITHSUNDEEP
amazon-web-servicesamazon-ec2amazon-elbterraform
Kostas Demiris
Kostas Demiris

Reputation: 3611

Cycle error in Terraform when combining ELB and Auto Scaling Group

I want to create an ASG with only 1 instance initially.

I want all the instances of this ASG to be behind an ELB.

So I set load_balancers = ["${aws_elb.Production-Web-ELB.name}"] in the resource "aws_autoscaling_group" "ProductionWeb-ScalingGroup" .

Now, when I write the code for the resource "aws_elb" "Production-Web-ELB", and I set instances = ["${aws_autoscaling_group.ProductionWeb-ScalingGroup.*.id}"], I get the error...

Error configuring: 1 error(s) occurred:

* Cycle: aws_autoscaling_group.ProductionWeb-ScalingGroup, aws_elb.Production-Web-ELB

I understand that this error means that the one resource references the other in a circle. To check it I comment out the load_balancers = ["${aws_elb.Production-Web-ELB.name}"] part and terraform plan without any error.

So my question is: Am I unable using Terraform to create an ASG with an attached ELB and every EC2 that will spawn inside it will be automatically behind the ELB ?

Is there something from the documentation that I missed?

Is there a workaround?

Upvotes: 1

Views: 676

Answers (1)

Anthony Neace
Anthony Neace

Reputation: 26023

You don't need to explicitly define the instances that will be associated with the ELB in terraform's ELB definition. By using the load_balancers argument, you're associating the ELB with the AutoScaling group, and AutoScaling will know to attach any instances that are created to that ELB when the AutoScaling group launches that instance.

Terraform isn't directly managing the state of the instances in this case -- AWS AutoScaling is, so their state likewise don't need to be defined in terraform beyond defining a launch configuration and associating it to the AutoScaling group.

To tell terraform to launch the AutoScaling group with a single instance, set your min_size argument to 1 and let your scaling policies handle the desired capacity from there. You could alternatively set desired_capacity to 1, but be wary of managing that state in terraform because it will set the desired_capacity to 1 every time you apply your plan.

Upvotes: 3

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