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Author : Daniel Sol January 2019

Private Preview : Prepare an existing RHEL/CentOS/OracleLinux 7.6 Linux Azure VM image for use with cloud-init

This article shows you how to take an existing Azure virtual machine and prepare it to be redeployed and ready to use cloud-init. The resulting image can be used to deploy a new virtual machine or virtual machine scale sets - either of which could then be further customized by cloud-init at deployment time. These cloud-init scripts run on first boot once the resources have been provisioned by Azure. For more information about how cloud-init works natively in Azure and the supported Linux distros, see cloud-init overview

Prerequisites

This document assumes you already have a running Azure virtual machine running a supported version of the Linux operating system. You have already configured the machine to suit your needs, installed all the required modules, processed all the required updates and have tested it to ensure it meets your requirements.

Preparing RHEL 7.6 / CentOS 7.6

Create a base VM to build the image:

az vm create \
  --resource-group <rgName> \
  --name <vmName> \
  --admin-username <userName> \
  --image OpenLogic:CentOS:7.6:latest \
  --ssh-key-value /sshKeyPath/sshKey.pub

You need to SSH into your Linux VM and run the following commands in order to install cloud-init.

sudo yum makecache fast
yum install -y gdisk cloud-utils-growpart
yum install - y cloud-init

Update the cloud_init_modules section in /etc/cloud/cloud.cfg to include the following modules:

- disk_setup
- mounts

Here is a sample of what a general-purpose cloud_init_modules section looks like.

cloud_init_modules:
 - migrator
 - bootcmd
 - write-files
 - growpart
 - resizefs
 - disk_setup
 - mounts
 - set_hostname
 - update_hostname
 - update_etc_hosts
 - rsyslog
 - users-groups
 - ssh

A number of tasks relating to provisioning and handling ephemeral disks need to be updated in /etc/waagent.conf. Run the following commands to update the appropriate settings.

sed -i 's/Provisioning.Enabled=y/Provisioning.Enabled=n/g' /etc/waagent.conf
sed -i 's/Provisioning.UseCloudInit=n/Provisioning.UseCloudInit=y/g' /etc/waagent.conf
sed -i 's/ResourceDisk.Format=y/ResourceDisk.Format=n/g' /etc/waagent.conf
sed -i 's/ResourceDisk.EnableSwap=y/ResourceDisk.EnableSwap=n/g' /etc/waagent.conf
cloud-init clean

Find the Azure datasource sooner, by creating a new file /etc/cloud/cloud.cfg.d/91-azure_datasource.cfg using an editor of your choice with the following lines:

# This configuration file is used to connect to the Azure DS sooner
datasource_list: [ Azure ]

If your existing Azure image has a swap file configured and you want to change the swap file configuration for new images using cloud-init, you need to remove the existing swap file.

For Red Hat based images - follow the instructions in the following Red Hat document explaining how to remove the swap file.

For CentOS and Oracle Linux images with swapfile enabled, you can run the following command to turn off the swapfile:

sudo swapoff /mnt/resource/swapfile

Ensure the swapfile reference is removed from /etc/fstab - it should look something like the following output:

# /etc/fstab
# Accessible filesystems, by reference, are maintained under '/dev/disk'
# See man pages fstab(5), findfs(8), mount(8) and/or blkid(8) for more info
#
UUID=99cf66df-2fef-4aad-b226-382883643a1c / xfs defaults 0 0
UUID=7c473048-a4e7-4908-bad3-a9be22e9d37d /boot xfs defaults 0 0

To save space and remove the swap file you can run the following command:

rm /mnt/resource/swapfile -f

NOTE If you want to use a swap file, you must add code in your image to set this up (this doc will be updated soon with an example).

Extra step for cloud-init prepared image

Note

If your image was previously a cloud-init prepared and configured image, you need to do the following steps.

The following three commands are only used if the VM you are customizing to be a new specialized source image was previously provisioned by cloud-init. You do NOT need to run these if your image was configured using the Azure Linux Agent.

sudo cloud-init clean --logs
sudo waagent -deprovision+user -force

Finalizing Linux Agent setting

All Azure platform images have the Azure Linux Agent installed, regardless if it was configured by cloud-init or not. Run the following command to finish deprovisioning the user from the Linux machine.

sudo waagent -deprovision+user -force

For more information about the Azure Linux Agent deprovision commands, see the Azure Linux Agent for more details.

Exit the SSH session, then from your bash shell, run the following AzureCLI commands to deallocate, generalize and create a new Azure VM image. Replace myResourceGroup and sourceVmName with the appropriate information reflecting your sourceVM.

az vm deallocate --resource-group myResourceGroup --name sourceVmName
az vm generalize --resource-group myResourceGroup --name sourceVmName
az image create --resource-group myResourceGroup --name myCloudInitImage --source sourceVmName

Complete Script

yum makecache fast
echo install cloud-init dependencies 
yum install -y gdisk cloud-utils-growpart
echo install of cloud-init
yum install -y cloud-init

sed -i '/ - mounts/d' /etc/cloud/cloud.cfg
sed -i '/ - disk_setup/d' /etc/cloud/cloud.cfg
sed -i '/cloud_init_modules/a\\ - mounts' /etc/cloud/cloud.cfg
sed -i '/cloud_init_modules/a\\ - disk_setup' /etc/cloud/cloud.cfg
cloud-init clean

echo waagent provisioning config turned off
sed -i 's/Provisioning.Enabled=y/Provisioning.Enabled=n/g' /etc/waagent.conf
sed -i 's/Provisioning.UseCloudInit=n/Provisioning.UseCloudInit=y/g' /etc/waagent.conf
sed -i 's/ResourceDisk.Format=y/ResourceDisk.Format=n/g' /etc/waagent.conf
sed -i 's/ResourceDisk.EnableSwap=y/ResourceDisk.EnableSwap=n/g' /etc/waagent.conf
        
echo removing swapfile - oralinux uses a swapfile by default
swapoff /mnt/resource/swapfile
rm /mnt/resource/swapfile -f


echo Set DS properties - not setting this causes 2s delay
cat > /etc/cloud/cloud.cfg.d/91-azure_datasource.cfg <<EOF
# This configuration file is used to connect to the Azure DS sooner
datasource_list: [ Azure ]
EOF
        
echo waagent deprovisioning
/usr/sbin/waagent -force -deprovision+user && export HISTSIZE=0 && sync