terraform-kvm

A Terraform module for Kernel Virtual Machines (KVM/libvirt) utilizing terraform-provider-libvirt.

Description

The module allows creating and provisioning virtual machine fleets using different mechanisms after implementing a manageable underlying infrastructure.

It is composed of two modules actually:

• kvm-common: creates a storage pool and defines a base volume. The module call was appended to provider.tf for the sake of simplicity.
• kvm: runs per VM (or VM group) and adds child volumes, prepares the cloud-init image/s, renders the required templates and creates the domain/s.

Compatibility

Tested under CentOS 7 and AlmaLinux 9.

Requirements

A host server

A preconfigured host server prepared for libvirt. During development I put together an Ansible playbook available from ansible-host-server and tested under CentOS 7.

Terraform

Terraform manual installation is quite straightforward

wget https://releases.hashicorp.com/terraform/1.5.7/terraform_1.5.7_linux_amd64.zip
unzip terraform_1.5.7_linux_amd64.zip
sudo mv terraform /usr/local/bin/terraform

Configuration

main.tf holds the specification for our deployment. The files under examples/ can be renamed and used to that purpose straight away.

Input variables

main

Name	Type	Description	Default
deploy_account	string	Deployment account username	deploy
host_server	string	Host server IP address	""

kvm

Name	Type	Description	Default
hostname	string		guest
domain	string	Search domain	local
memory	number	Memory in megabytes	512
vcpu	number	Number of virtual cores	1
size	number	Virtual disk size in bytes	16 GB
method	string	Address assign method, either static or dhcp	dhcp
address	string	IP address in CIDR notation	""
gateway	string	Default gateway	""
dns_1	string	Primary nameserver	""
dns_2	string	Secondary nameserver	""
deploy_account	string	Deployment account username	deploy
deploy_account_pwd	string	Deployment account password	""
bridge_interface	string	Host bridge interface name	"br0"

kvm-common

Name	Type	Description	Default
pool_path	string	Virtual disk path	/mnt/kvm/disks
image	string	Source qcow2 base image URL	AlmaLinux 9.3

Implementing

The infrastructure can be planned, applied and destroyed by means of

terraform init
terraform plan
terraform apply -auto-approve
terraform destroy -auto-approve

During creation Terraform will use cloud-init to create a privileged deployment account inside the VMs and provide the SSH key found in keys/id_rsa.pub, so as to prepare the guest systems to be accessed by further provisioning systems.

Examples

Single statically addressed VM

module "guest01" {
  source = "./kvm"
  depends_on = [module.common]
  hostname = "guest01"
  method = "static"
  address = "10.12.0.111/24"
  gateway = "10.12.0.1"
}

Multiple VMs with random hostnames

variable "instances" { default = 3 }

resource "random_string" "hostname" {
  length = 4
  special = false
  upper = false
  count = "${var.instances}"
}

module "guests" {
  source = "./kvm"
  depends_on = [module.common]
  hostname = "${random_string.hostname[count.index].result}"
  count = "${var.instances}"
}

Which created three VMs

[root@host deploy]# virsh list
 Id    Name                           State
----------------------------------------------------
 1     adym                           running
 2     yw6q                           running
 3     e4r3                           running

Alongside their volumes

/mnt/kvm/disks/base.qcow2
/mnt/kvm/disks/adym-commoninit.iso
/mnt/kvm/disks/adym.qcow2
/mnt/kvm/disks/e4r3-commoninit.iso
/mnt/kvm/disks/e4r3.qcow2
/mnt/kvm/disks/yw6q-commoninit.iso
/mnt/kvm/disks/yw6q.qcow2

Please, browse the examples/ folder for further scripts.

References

• dmacvicar/libvirt (Terraform Registry)
• cloud-init
• fabianlee/terraform-libvirt-ubuntu-examples
• MonolithProjects/terraform-libvirt-vm