Skip to content

Latest commit

 

History

History
160 lines (87 loc) · 3.68 KB

README.md

File metadata and controls

160 lines (87 loc) · 3.68 KB

Terraform : Project2:

==================

Objective:

I want to create multiple compute instances(identical configuration, except different cloudinit bootscripts - application provisioning ) and associate floating IPs.

Infrastructure Diagram

Technical learning:

  • count parameter

  • element

  • conditional execution

Part1 - Create Multiple compute Instances:

1. create a number of instances in vars.tf file

variable instances {
   type = "map"   
   
   default   {     
   backend = "2"   
   } 
 }

we created a map (python terminology - its dictionary, sting keys to string values) , this can be accessed as vars.instances["backend"]. This variable will return the value 2.

Reference : https://www.terraform.io/docs/configuration/variables.html#maps

2. In stack.tf, the openstack_compute_instance_v2 resource creation block,

specify the number of resources to be created as below,

  count = "${var.instances["backend"]}"

Here the count is 2. it means index 0 and 1.

Reference: https://www.terraform.io/docs/configuration/resources.html#count

3. Access the index of the instance count.

We populate the VM name from index count index.

 name = "myvm1_${count.index}"

we can get the index of the count using "count.index" attribute.

4. conditional execution:

Terraform supports the simple conditional execution to branch on the final value

The conditional syntax is the well-known ternary operation:

CONDITION ? TRUEVAL : FALSEVAL

our objective is simply, run separate cloudinit for 1st server and separate one for second server. we use count.index to identify as below,

user_data = "${count.index > 0 ? "${data.template_cloudinit_config.init_script_2.rendered}" : "${data.template_cloudinit_config.init_script_1.rendered}"}"

Reference: https://www.terraform.io/docs/configuration/interpolation.html#conditionals

Part2 - Associate the Floatingips

1. create a the 'n' number of floating ip resources (using count attribute)

resource "openstack_networking_floatingip_v2" "fip_1" {
  pool = "public"
  count = "${var.instances["backend"]}"
}

2. Associate the floating ip - using element() inbuilt funtion

In earlier exercises, we use direct association of VM id and floating ip id as below,

resource "openstack_compute_floatingip_associate_v2" "fip_1" {
  floating_ip = "${openstack_networking_floatingip_v2.fip_1.address}"
  instance_id = "${openstack_compute_instance_v2.vm1.id}"
}

But in this stack/example, we cannot access the floatingip resource id and instance id as string. Because we have used count parameters.

resource "openstack_networking_floatingip_v2" "fip_1" {
  pool = "public"
  count = "${var.instances["backend"]}"
}

Hence we created multiple resources(list) on same id, The ID contains the list of resources.

We can access this resources by

openstack_networking_floatingip_v2.fip_1.*.id

To access a single resource from the list of resources, element in-built function is used.

resource "openstack_compute_floatingip_associate_v2" "fip_1" {
  count = "${var.instances["backend"]}"
  floating_ip = "${element(openstack_networking_floatingip_v2.fip_1.*.address, count.index)}"
  instance_id = "${element(openstack_compute_instance_v2.vm1.*.id, count.index)}"
}

Reference:

https://www.terraform.io/docs/configuration/interpolation.html#element-list-index-

References:

  1. https://www.terraform.io/docs/configuration/resources.html#count
  2. https://www.terraform.io/docs/configuration/interpolation.html#conditionals
  3. https://www.terraform.io/docs/configuration/resources.html#using-variables-with-count