Cloud-init support for virtual machines in Azure

This article explains the support that exists for cloud-init to configure a virtual machine (VM) or virtual machine scale sets (VMSS) at provisioning time in Azure. These cloud-init scripts run on first boot once the resources have been provisioned by Azure.

Cloud-init overview

Cloud-init is a widely used approach to customize a Linux VM as it boots for the first time. You can use cloud-init to install packages and write files, or to configure users and security. Because cloud-init is called during the initial boot process, there are no additional steps or required agents to apply your configuration. For more information on how to properly format your #cloud-config files, see the cloud-init documentation site. #cloud-config files are text files encoded in base64.

Cloud-init also works across distributions. For example, you don't use apt-get install or yum install to install a package. Instead you can define a list of packages to install. Cloud-init automatically uses the native package management tool for the distro you select.

We are actively working with our endorsed Linux distro partners in order to have cloud-init enabled images available in the Azure marketplace. These images will make your cloud-init deployments and configurations work seamlessly with VMs and VM Scale Sets (VMSS). The following table outlines the current cloud-init enabled images availability on the Azure platform:

Publisher Offer SKU Version cloud-init ready
Canonical UbuntuServer 16.04-LTS latest yes
Canonical UbuntuServer 14.04.5-LTS latest yes
CoreOS CoreOS Stable latest yes
OpenLogic CentOS 7-CI latest preview
RedHat RHEL 7-RAW-CI latest preview

Currently Azure Stack does not support the provisioning of RHEL 7.4 and CentOS 7.4 using cloud-init.

What is the difference between cloud-init and the Linux Agent (WALA)?

WALA is an Azure platform-specific agent used to provision and configure VMs, and handle Azure extensions. We are enhancing the task of configuring VMs to use cloud-init instead of the Linux Agent in order to allow existing cloud-init customers to use their current cloud-init scripts. If you have existing investments in cloud-init scripts for configuring Linux systems, there are no additional settings required to enable them.

If you do not include the Azure CLI --custom-data switch at provisioning time, WALA takes the minimal VM provisioning parameters required to provision the VM and complete the deployment with the defaults. If you reference the cloud-init --custom-data switch, whatever is contained in your custom data (individual settings or full script) overrides the WALA defaults.

WALA configurations of VMs are time-constrained to work within the maximum VM provisioning time. Cloud-init configurations applied to VMs do not have time constraints and will not cause a deployment to fail by timing out.

Deploying a cloud-init enabled Virtual Machine

Deploying a cloud-init enabled virtual machine is as simple as referencing a cloud-init enabled distribution during deployment. Linux distribution maintainers have to choose to enable and integrate cloud-init into their base Azure published images. Once you have confirmed the image you want to deploy is cloud-init enabled, you can use the Azure CLI to deploy the image.

The first step in deploying this image is to create a resource group with the az group create command. An Azure resource group is a logical container into which Azure resources are deployed and managed.

The following example creates a resource group named myResourceGroup in the eastus location.

az group create --name myResourceGroup --location eastus

The next step is to create a file in your current shell, named cloud-init.txt and paste the following configuration. For this example, create the file in the Cloud Shell not on your local machine. You can use any editor you wish. Enter sensible-editor cloud-init.txt to create the file and see a list of available editors. Choose #1 to use the nano editor. Make sure that the whole cloud-init file is copied correctly, especially the first line:

#cloud-config
package_upgrade: true
packages:
  - httpd

Press ctrl-X to exit the file, type y to save the file and press enter to confirm the file name on exit.

The final step is to create a VM with the az vm create command.

The following example creates a VM named centos74 and creates SSH keys if they do not already exist in a default key location. To use a specific set of keys, use the --ssh-key-value option. Use the --custom-data parameter to pass in your cloud-init config file. Provide the full path to the cloud-init.txt config if you saved the file outside of your present working directory. The following example creates a VM named centos74:

az vm create \
  --resource-group myResourceGroup \
  --name centos74 \
  --image OpenLogic:CentOS:7-CI:latest \
  --custom-data cloud-init.txt \
  --generate-ssh-keys 

When the VM has been created, the Azure CLI shows information specific to your deployment. Take note of the publicIpAddress. This address is used to access the VM. It takes some time for the VM to be created, the packages to install, and the app to start. There are background tasks that continue to run after the Azure CLI returns you to the prompt. You can SSH into the VM and use the steps outlined in the Troubleshooting section to view the cloud-init logs.

Troubleshooting cloud-init

Once the VM has been provisioned, cloud-init will run through all the modules and script defined in --custom-data in order to configure the VM. If you need to troubleshoot any errors or omissions from the configuration, you need to search for the module name (disk_setup or runcmd for example) in the cloud-init log - located in /var/log/cloud-init.log.

Note

Not every module failure results in a fatal cloud-init overall configuration failure. For example, using the runcmd module, if the script fails, cloud-init will still report provisioning succeeded because the runcmd module executed.

For more details of cloud-init logging, refer to the cloud-init documentation

Next steps

For cloud-init examples of configuration changes, see the following documents: