Terraform and OpenStack: Boot an instance from CD-ROM
In the spirit of "this took me way too long", here's how to boot an instance with a CD-ROM on OpenStack, using Terraform.
Why would I need this?
In a perfect world, I have templates to bootstrap instances. Means, the instances are ready to go when booted. I customise them with cloud-init and let them do all kinds of cool (or necessary) stuff like configuring the network, setting hostnames, adding user accounts and then maybe joining them to a cluster.
But I don't live in a perfect world, still: I try to automate as much as I can. So I don't have to remember any of it.
Use-case
The use-case is the installation (or setup) of a SoPhos firewall. The vendor provides me with an image which can be booted and then an installer and setup wizard have to be completed to finish the installation process.
Using Terraform
Let's look at the code first - the following is used to create the instance:
resource "openstack_compute_instance_v2" "vpn_host" {
depends_on = [
data.openstack_images_image_v2.vpn_image
]
name = "vpn"
flavor_name = "dynamic-M1"
security_groups = [
"default",
]
# boot device
block_device {
source_type = "blank"
volume_size = "100"
boot_index = 0
destination_type = "volume"
delete_on_termination = false
}
# cd-rom
block_device {
uuid = data.openstack_images_image_v2.vpn_image.id
source_type = "image"
destination_type = "volume"
boot_index = 1
volume_size = 1
device_type = "cdrom"
}
network {
port = openstack_networking_port_v2.vpn_port.id
}
network {
uuid = data.openstack_networking_network_v2.public_network.id
}
}
I am omitting some code, but let's walk through this.
How to CD-ROM (block_device)
I am approaching this in reverse order — let me talk about the second block_device block first.
This is the bit that took me the longest because I didn't know how disk_bus or device_type play well together. Or which of the two is needed.
The moral of the story is, if the Terraform provider documentation is too vague, read OpenStack's documentation on device mapping instead. Or in your case, you are reading my blog post! :-)
To continue, the image of the SoPhos firewall is referenced by data.openstack_images_image_v2.vpn_image.id. Therefor, I have a data provider which pulls the image from OpenStack (or Glance):
data "openstack_images_image_v2" "vpn_image" {
name = "fancy readable name of the ISO here"
}
During terraform apply Terraform will try to resolve it. If successful its result will be used to create a (Cinder) volume from it. The "1 (GB)" size of the volume is what OpenStack suggested when I did this via the fancy web UI. Therefor, I used it in my Terraform setup.
The important part of the block_device block is device_type = "cdrom". Without it OpenStack will refuse to boot from the volume even though we provide a boot_index.
Small caveat: I had to add a depends_on as Terraform's dependency graph would not wait for the data provider to resolve during apply.
Boot device
Last but not least: I also need a bootable root partition to install to, and that's the first block_device block in my code snippet.
If all goes well, the provisioning is as follows:
- OpenStack starts the instance
- It discovers that the first disk is not bootable (yet)
- It proceeds with the CD-ROM (attached to
/dev/hdain my case).
After the installation is finished, subsequent reboots of the instance always use the first disk. This is similar to dropping a CD into a (real) server, installing it (from the CD) and leaving the CD (in the drive) at the data center (just in case). :-)
The rest
The rest is hopefully straight forward.
I defined two other networks (with another Terraform run) which are used via data providers.
One is used as a port (for fixed IP allocation/configuration, openstack_networking_port_v2.vpn_port.id) and the other provides the VPN instance with another accessible IP for dial-in and remote management from the public network (via data.openstack_networking_network_v2.public_network.id).
Fin
Thanks for reading.
