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Creation host on Nectar

This document describes how to create a Nectar virtual machine instance to act as the creation host system for creating images.

Process

Step 1: Instantiate VM instance for the host system

Instantiate a virtual machine instance to use as the creation host. And configure the security groups to allow ssh acccess to the instance.

While the Nectar Melbourne Availability Zone is physically closest to the Glance image store, the instance can be launched in any Availability Zone.

The most critical factor is having enough disk space. If the VM instance does not have enough disk space, attaching Volume Storage to it can be an option (if your project has access to it). It needs to have enough space for the ISO files, the image file that will be created, the operating system and software.

The second most critical factor is performance. The virtual machine instance that will be run by QEMU will be configured to have 2 vCPUs and 4 GiB of RAM (though this can be changed by editing the script). Therefore, the creation host needs to be larger than that.

Step 2: Install necessary packages

The following packages are required:

  • QEMU hypervisor is needed to create the image; and

  • the OpenStackclient (in particular the glance component) is needed to upload the image.

Login to the creation host system and install those packages.

The steps to install them will be different for different Linux distributions, and there are different approaches that can be taken. For example, the OpenStack client tools can be installed from a repository, or installed as Python packages (either installed into the system or in a Python virtual environment). Some example installation steps are shown below.

CentOS 7:

[local]$ ssh [email protected]

[ec2-user@host] sudo yum update -y

[ec2-user@host] sudo yum install -y qemu-kvm

[ec2-user@host]$ sudo yum install -y python3
[ec2-user@host]$ sudo pip3 install --upgrade pip
[ec2-user@host]$ sudo pip3 install python-openstackclient

CentOS 8 Stream:

Note: currently the process does not work properly on CentOS 8 and CentOS 8 Stream. Everything works except the guest VM cannot connect to the Internet. So please use one of the other distributions until this problem is solved.

The same as for CentOS 7, except there might be an error saying: Cannot uninstall 'PyYAML'. It is a distutils installed project and thus we cannot accurately determine which files belong to it which would lead to only a partial uninstall.

If that error occurs, run the following to install PyYAML

[ec2-user@host]$ sudo pip3 install --ignore-installed PyYAML

And then run the pip install for python-openstackclient. Without the --ignore-installed option, pip attempts to uninstall the old version of the package before installing the new version. But that fails, as the error message says, because it does not know how to properly uninstall the old version. The option tells pip to install the new version over the old version, without first uninstalling it. There are probably other ways around this too, such as uninstalling PyYAML first or installing the OpenStack client in a Python virtual environment.

Ubuntu 20.04:

[local]$ ssh [email protected]

[ubuntu@host]$ sudo apt-get -y update

[ubuntu@host]$ sudo apt-get -y install -y qemu-kvm

[ubuntu@host]$ sudo apt-get -y install python3-pip
[ubuntu@host]$ sudo pip3 install --upgrade pip
# Log out and log back in to use the new version

[ubuntu@host]$ sudo pip3 install python-openstackclient

Step 3: Create a user account on the creation host

Any user account can be used to create the image, but in this example a separate "creator" account will be created for it.

[ec2-user@host]$ sudo adduser creator

On Ubuntu's version of adduser, include the --disabled-password option.

Identify a working directory to store the files. The volume it is on must have enough available space to store the ISO and image files (e.g. 20 GiB free).

[ec2-user@host]$ sudo mkdir /mnt/creator
[ec2-user@host]$ sudo chown creator:creator /mnt/creator

Finally set up access to the creator account. Normally, this can be done by adding your SSH public key to it.

[ec2-user@host]$ sudo mkdir /home/creator/.ssh
[ec2-user@host]$ sudo cp ~/.ssh/authorized_keys /home/creator/.ssh/authorized_keys
[ec2-user@host]$ sudo chown -R creator:creator /home/creator/.ssh

Log out of the creation host.

[ec2-user@host]$ exit

See also