Extrapolating the instance name as part of the module about terraform-aws-ec2-instance

[omahonyb]

I am just wondering how to get that out as part of the user data:

#!/bin/bash
#Set hostname
hostnamectl set-hostname ${lookup(module.ec2_bastion.tags[count.index], "Name")}
#Setup Chrony to point at AWS
sed -i '/^server [1-3]/d' /etc/chrony.conf
sed -i 's/0.centos.pool.ntp.org iburst/169.254.169.123 prefer iburst minpoll 4 maxpoll 4/g' /etc/chrony.conf
systemctl restart chronyd
EOF

I get the error "Error: module "ec2_bastion": count variables are only valid within resources"

[antonbabenko]

Tags are outputs from this module and can be referenced as module.my_ec2.tags where my_ec2 is the module name. The output looks like this:

tags = [
  {
    "Env" = "Private"
    "Location" = "Secret"
    "Name" = "example-normal-1"
  },
  {
    "Env" = "Private"
    "Location" = "Secret"
    "Name" = "example-normal-2"
  },
]

There are other outputs as lists you can use to identify instance ids or IPs.

[bryantbiggs]

hi @omahonyb, you can do one of two routes:

1. Within your user_data script you can query the metadata endpoint API and get the hostname dynamically: curl http://169.254.169.254/latest/meta-data/hostname

2. You can inject the name into your user_data script during deployment. To do this, create a local file called something like userdata.sh with the following contents:

#!/bin/bash
# Set hostname
hostnamectl set-hostname ${hostname}
# Setup Chrony to point at AWS
sed -i '/^server [1-3]/d' /etc/chrony.conf
sed -i 's/0.centos.pool.ntp.org iburst/169.254.169.123 prefer iburst minpoll 4 maxpoll 4/g' /etc/chrony.conf
systemctl restart chronyd

Then in the code for your instance(s) you can add:

module "ec2" {
  source = "../../"

  instance_count = 1

  name          = "example-normal"
  ami           = data.aws_ami.amazon_linux.id
  instance_type = "c5.large"
  subnet_id     = tolist(data.aws_subnet_ids.all.ids)[0]

  vpc_security_group_ids      = [module.security_group.this_security_group_id]
  associate_public_ip_address = true
  placement_group             = aws_placement_group.web.id

  user_data_base64 = base64encode(templatefile("${path.module}/userdata.sh", {
    hostname = "example-normal"
  }))

Note - this approach has a flaw if the instance count is greater than 1 and the use_num_suffix value is true as the name is dynamically generated and will not be injected correctly to your user_data

[kclinden]

@bryantbiggs - Anyway to get that 2nd option to work with userdata and multiple instances? It is possible to access the count variable?

[antonbabenko]

Closing this issue. v3.0.0 (released today) has better support for handling instance names as part of the module.

[github-actions]

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