Retrieve auto scaling group instance ip's and provide it to ansible - mongodb

Question

Im currently developing terraform script and ansible roles in order to install mongodb with the replication. im using auto scaling group and i need to pass, ec2 instance private ip's to ansible as extra vars. is there any way to do that?
When it's come to rs.initiate() is there any way to add ec2 private ip to mongo cluster when terraform creating the instances.

Answer 1

Not really sure about how it's done in ASGs, probably a combination of user-data and EC2 metadata would be helpful.
But I do it as below in case we have a fixed number of nodes. Posting this answer as it can be helpful to someone in some way.
Using EC2 dynamic inventory scripts.
Ref - https://docs.ansible.com/ansible/2.5/user_guide/intro_dynamic_inventory.html
This is basically a python script i.e ec2.py which gets the instance private IP using tags etc. It comes with a config file named ec2.ini.
Tag your instance in TF script (you add a role tag) -
resource "aws_instance" "ec2" {
....
tags = "${merge(var.tags, map(
"description","mongodb-node",
"role", "mongodb-node",
"Environment", "${local.env}",))}"
}
output "ip" {
value = ["${aws_instance.ec2.private_ip}"]
}
Get the instance private IP in playbook -
- hosts: localhost
connection: local
tasks:
- debug: msg="MongoDB Node IP is - {{ hostvars[groups['tag_role_mongodb-node'][0]].inventory_hostname }}"
Now run the playbook using TF null_resource -
resource null_resource "ansible_run" {
triggers {
ansible_file = "${sha1(file("${path.module}/${var.ansible_play}"))}"
}
provisioner "local-exec" {
command = "ANSIBLE_HOST_KEY_CHECKING=False ansible-playbook -i ./ec2.py --private-key ${var.private_key} ${var.ansible_play}"
}
}
You got to make sure AWS related environment variables are present/exported for ansible to fetch AWS EC2 metadata. Also make sure ec2.py is executable.
If you want to get the private IP, change the following config in ec2.ini -
destination_variable = private_ip_address
vpc_destination_variable = private_ip_address