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Issues using VM extensions in Python 3-enabled Linux Azure Virtual Machines systems

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Note

Microsoft encourages users to adopt Python 3.x in their systems unless your workload requires Python 2.x support. Examples of this requirement might include legacy administration scripts, or extensions such as Azure Disk Encryption and Azure Monitor.

Before installing Python 2.x in production, consider the question of long-term support of Python 2.x, particularly their ability to receive security updates. As products, including some of the extension mentioned, update with Python 3.8 support, you should discontinue use of Python 2.x.

Some Linux distributions have transitioned to Python 3.8 and removed the legacy /usr/bin/python entrypoint for Python altogether. This transition impacts the out-of-the-box, automated deployment of certain virtual machine (VM) extensions with these two conditions:

  • Extensions that are still transitioning to Python 3.x support
  • Extensions that use the legacy /usr/bin/python entrypoint

Linux distribution users who have transitioned to Python 3.x must ensure the legacy /usr/bin/python entrypoint exists before attempting to deploy those extensions to their VMs. Otherwise, the extension deployment might fail.

  • Endorsed Linux distributions that are affected include Ubuntu Server 20.04 LTS and Ubuntu Pro 20.04 LTS.

  • Affected VM Extensions include Azure Disk Encryption, Log Analytics, VM Access (used for Password Reset), and Guest Diagnostics (used for additional performance counters).

In-place upgrades, such as upgrading from Ubuntu 18.04 LTS to Ubuntu 20.04 LTS, should retain the /usr/bin/python symlink, and remain unaffected.

Resolution

Consider these general recommendations before deploying extensions in the known-affected scenarios described previously in the Summary:

  1. Before deploying the extension, reinstate the /usr/bin/python symlink by using the Linux distribution vendor-provided method.

    • For example, for Python 2.7, use: sudo apt update && sudo apt install python-is-python2

  2. This recommendation is for Azure customers and isn't supported in Azure Stack:

    • If you’ve already deployed an instance that exhibits this problem, use the Run command functionality in the VM blade to run the commands mentioned above. The Run command extension itself isn't affected by the transition to Python 3.8.

  3. If you're deploying a new instance, and need to set an extension at provisioning time, use cloud-init user data to install the packages mentioned above.

    For example, for Python 2.7:

    # create cloud-init config
cat > cloudinitConfig.json <<EOF
#cloud-config
package_update: true

runcmd:
- sudo apt update
- sudo apt install python-is-python2 
EOF

# create VM
az vm create \
    --resource-group <resourceGroupName> \
    --name <vmName> \
    --image <Ubuntu 20.04 Image URN> \
    --admin-username azadmin \
    --ssh-key-value "<sshPubKey>" \
    --custom-data ./cloudinitConfig.json

  4. If your organization’s policy administrators determine that extensions shouldn’t be deployed in VMs, you can disable extension support at provisioning time:

    • REST API

      To disable and enable extensions when you can deploy a VM with this property:

        "osProfile": {
    "allowExtensionOperations": false
  },

Next steps

Please refer to Other base system changes since 18.04 LTS - Python 3 by default for additional information.