CentOS 7 Template VM

This guide describes how to create a template VM for vSphere running CentOS 7. The template VM is supposed to be compatible with Terraform, Kubermatic KubeOne, and Kubermatic machine-controller.

Requirements

You need to satisfy the following requirements before proceeding:

• Have access to the vSphere API via govc and vCenter
• Have the following tools installed on your local machine: govc, qemu-img, and virt-customize (comes with the libguestfs-tools package)

Preparing Local Environment

Before getting started, you should prepare your local environment by exporting GOVC_ environment variables with the information about your vSphere setup:

export GOVC_URL="https://<url>"
export GOVC_USERNAME="<username>"
export GOVC_PASSWORD="<password>"
export GOVC_INSECURE=false # set to true if you don't have a valid/trusted certificate
export GOVC_DATASTORE="<datastore-name>"

Downloading CentOS 7 VM

We’ll download CentOS 7 qcow2 image. qcow2 is a hard drive with preinstalled CentOS 7 that can be used for creating (vSphere) VMs. That being said, you don’t need to install CentOS manually, that’s already done for you.

The qcow2 image can be downloaded from the official CentOS website. Download the latest available qcow2 file. At the time of writing this document, the latest available file is called CentOS-7-x86_64-GenericCloud-2111.qcow2. It’s recommended to verify checksums, but we’ll omit that because of brevity.

Preparing and Uploading the CentOS qcow2 File

The downloaded CentOS installation comes in qcow2 format, however, we need VMDK format so that it can be used with vSphere. Additionally, we need to login to the VM to configure it. The installation comes with root and centos users, but neither has a password set, so it’s not possible to login to the VM using those users.

First, we’ll set the password for the root user using the virt-customize tool:

sudo virt-customize -a CentOS-7-x86_64-GenericCloud-2111.qcow2 --root-password 'password:<insert-your-password-here>'

Customizing the VM might take a minute or two. Once that’s done, we can convert the qcow2 file to vmdk using qemu-img:

qemu-img convert -O vmdk -o subformat=streamOptimized "./CentOS-7-x86_64-GenericCloud-2111.qcow2" "CentOS-7-x86_64-GenericCloud-2111.vmdk"

Converting the image to vmdk might take several minutes. Finally, once that is done, we can upload the vmdk file to vSphere using govc or using vCenter. We’ll use govc for purposes of this guide:

govc import.vmdk -dc=<datacenter-name> -pool=/<datacenter-name>/host/<cluster-name>/Resources -ds=<datastore-name> "./CentOS-7-x86_64-GenericCloud-2111.vmdk"

That might take a few minutes depending on your internet connection speed. In the next step, we’ll create a new vSphere VM using the uploaded vmdk file as the hard drive.

Creating a Template VM

Go to vCenter and create a new Virtual Machine. You can name and place the VM however you prefer. When asked about compatibility, choose the latest available compatibility level. For Guest OS, choose Linux and CentOS 7 (64bit).

When asked to customize the hardware, you should take the following steps:

• remove the existing hard drive
• click on Add New Device and choose Existing Hard Disk
  • Find the uploaded vmdk file and then click on the OK button
• choose Client Device for New CD/DVD Drive and ensure that Device Mode is set to Passthrough Mode for that CD/DVD drive

Proceed with creating the VM. Once the VM is created, power it on and proceed to the next step.

Preparing the VM

We’ll configure the VM to be used as a template VM by KubeOne and machine-controller. Before proceeding, power on the VM via vCenter and open the Web Console or connect to the VM via SSH.

Once the VM is booted, you’ll see a prompt to enter credentials in the Web Console. Login with username root and use the password that you’ve chosen earlier.

As a first step, make sure that the VM is up-to-date:

yum update

Next, ensure that you have the following packages installed:

yum install \
  cloud-init \
  open-vm-tools \
  curl \
  wget \
  sudo \
  vim \
  epel-release

Once the epel-release package is installed, you can install pip which will be used later:

yum install python2-pip

Ensure that a service for VMware Tools is enabled and started:

systemctl enable --now vmtoolsd

CentOS 7 comes with an old version of cloud-init which does not support VMware Tools as a datasource for cloud-config. We’ll download a vSphere datastore plugin from VMware that extends cloud-init in a way that it can be used with VMware Tools. The project is called cloud-init-guestinfo and it’s available on GitHub. The project is archived because it has been integrated into cloud-init, but as mentioned, CentOS 7 is using an older cloud-init version without this datasource plugin.

The easiest way to install the latest version of this datasource plugin is by using the install script:

curl -sSL https://raw.githubusercontent.com/vmware/cloud-init-vmware-guestinfo/master/install.sh | sh -

The script will use pip (which we installed earlier) to download needed dependencies and install the cloud-init datasource plugin.

Once the datasource plugin is installed, we need to adjust the plugin’s configuration to allow using it alongside with the integrated NoCloud datasource plugin. The NoCloud datasource plugin is required by Kubermatic machine-controller. Open the following configuration file in a text editor of your choice:

vi /etc/cloud/cloud.cfg.d/99-DataSourceVMwareGuestInfo.cfg

Replace datasource_list: [ "VMwareGuestInfo" ] with the following line:

datasource_list: [ "VMwareGuestInfo", "NoCloud" ]

If there are any additional adjustments that you want to make to the VM, you should do those adjustments now before proceeding.

As a final step, we’ll cleanup the VM so that it can be used as a template.

First, we’ll ensure that there’s no hardcoded MAC address in the network configuration. Run ip addr and note the name of your network interface, for example eth0. Locate and open a network configuration file for your network interface. Network configuration files are located in /etc/sysconfig/network-scripts and are named as ifcfg-<interface-name>. For example:

vi /etc/sysconfig/network-scripts/ifcfg-eth0

Locate the line starting with HWADDR=.... If there’s such line, remove it completely, then save the file and close the text editor. If there’s no such line, you don’t need to take any action and can just close the text editor.

Then, remove generated SSH host keys. They’ll be regenerated upon the next boot:

rm -f /etc/ssh/ssh_host_*

Proceed to remove logs from /var/log and installation logs from the /root directory:

find /var/log -type f -exec truncate --size=0 {} \;
rm -f /root/anaconda-ks.cfg /root/original-ks.cfg

We can also cleanup temporary directories:

rm -rf /tmp/* /var/tmp/*

To make sure VMs are provisioned from the template correctly, we also have to reset the seed and machine-id:

rm -f /var/lib/systemd/random-seed
echo -n > /etc/machine-id

Finally, to make sure that cloud-init works as expected, it’s recommended to clean the cloud-init data:

cloud-init clean
cloud-init clean -l

Finally, power off the VM:

poweroff

Conclusion

The VM configuration is now completely done and the VM can be used as a template VM for both Terraform and machine-controller.