ELB cannot be attached to multiple subnets in the same AZ

[moesy]

Current Setup:

• VPC in us-east-1
• private & public subnet in each availability zone

When explicitly specifying a list of availability zones through the "availability_zone" variable and subsequently defining the private subnets in those associated zones deployment through the "vpc_subnets" variable fails with the message below:

1 error(s) occurred:

* aws_elb.es_client_lb: 1 error(s) occurred:

* aws_elb.es_client_lb: InvalidConfigurationRequest: ELB cannot be attached to multiple subnets in the same AZ.
	status code: 409, request id:

This is likely due to vpc subnets being pulled automatically from the VPC and availability_zone variable not being respected. Unless it is a design feature that needs to be documented.

workaround:

• Delete all public subnets form VPC
• Deploy ES using terraform scripts
• Reconfigure public subnets

[synhershko]

The availability_zones variable should have been removed because we now pull this data as data. Would using those available zones work in your case or do you need to specify a subset of AZs?

[moesy]

@synhershko, unfortunately, the way data pulls currently it does not differentiate between public and private subnets hence the error where multiple subnets from the same AZ are being used.

[pranas]

The availability_zones variable should have been removed because we now pull this data as data.

In my case I went the opposite way and removed pulling availability_zones and subnets as data. We had subnets in our VPC I didn't want to use here so I made another var for subnets. I think this approach covers more use cases, would you merge it in if I open PR?

[synhershko]

@pranas sure, how would that work though? pulling AZs via data only if no var value was specified?

[pranas]

You could do the same thing as you did with AZs here. However, I actually went the stupid simple way by just requiring putting subnets in variables. I even deleted the forementioned code and require AZs in variables as well to make things simpler.

[tomerleib]

I was able to overcome this issue with by separating it to two different sections filtered by tag, so the ELB will be created using the correct public subnets and the instances will be created in the private subnets:
data "aws_subnet_ids" "public" {
vpc_id = "${data.aws_vpc.selected.id}"
filter {
name = "tag:public"
values = [""]
}
}

data "aws_subnet_ids" "private" {
vpc_id = "${data.aws_vpc.selected.id}"
filter {
name = "tag:private"
values = [""]
}
}

[cwarny]

I'm facing this problem as well. What is the recommended workaround?

[cwarny]

@tomerleib I'm trying your workaround but could you elaborate as to how to modify the other files after implementing the change mentioned above?

[synhershko]

Fixed by f776fb5