EC2. Load balancer. At least two subnets must be specified

18
votes

I'm trying to create and configure Load Balancer. The Availability Zones section has only one subnet and one zone for me.

I faced error:

At least two subnets must be specified.

Simple question - what should I do? thanks.

2
amazon-web-servicesamazon-ec2load-balancingelastic-load-balancer
Sounds like you need to create at least one more subnet in a different AZ for your region. Once created, it should be selectable when configuring your ELB. – dmulter
@dmulter yeap. I got it already. Add your answer. – Dmitry Grinko
@dmulter thanks, that worked. Key point was a different AZ for region. – Mykyta Chelombitko

2 Answers

12
votes

You'll first need to create two or more subnets in your VPC. It's typically good practice to create at least one subnet for each availability zone (AZ) in your region. Be sure to select public/private as is appropriate for your architecture.

There isn't a specific example in the AWS documentation, but be sure to first understand VPC concepts and the creation of subnets. See Scenarios and Examples for the closest example walkthroughs for creating subnets.

Selecting subnets when configuring an ELB should be straightforward now.

3
votes

You need two subnets in your VPC: good practice is to have one in two different availability zones, for instance a and b. The relevant section of TERRAFORM_CONFIG_NAME.tf would look something like this:

setting {
    namespace = "aws:ec2:vpc"
    name      = "Subnets"
    value     = "${lookup(var.vpc_subnets, format("%s_%s", var.location, var.availability_zone))}, ${lookup(var.vpc_subnets, format("%s_%s", var.location, var.secondary_availability_zone))}"
}

, variables.tf like this:

variable "vpc_subnets" {
  type = "map"
  default = {
    "frankfurt_a" = "subnet-12345671"
    "frankfurt_b" = "subnet-12345672"
    "frankfurt_c" = "subnet-12345673"
    "ireland_a" = "subnet-12345674"
    "ireland_b" = "subnet-12345675"
    "ireland_c" = "subnet-12345676"
  }
}

variable "availability_zone" {
  default = "a"
}

variable "secondary_availability_zone" {
  default = "b"
}


variable "regions" {
  type = "map"
  default = {
    "frankfurt" = "eu-central-1"
    "ireland" = "eu-west-1"
    "london" = "eu-west-2"
  }
}

variable "location" {
  default = "ireland"
}