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The metadata server provides information about a Compute Engine instance's scheduling options and settings, through the scheduling/ metadata directory listing and the maintenance-event metadata key. You can use these metadata keys to learn about a VM's scheduling options, and also to notify you of an upcoming maintenance event.

The metadata server receives maintenance event notices before a compute instance is live migrated or terminated. To learn more about maintenance events and instance behavior during the events, see Host maintenance overview.

For a specific set of VMs, your VM maintenance options are more flexible. To learn more, see Monitor and plan for a host maintenance event.

Before you begin

• For Windows Server VMs, use PowerShell 3.0 or later. We recommend that you use ctrl+v to paste the copied code blocks.
• If you haven't already, set up authentication. Authentication verifies your identity for access to Google Cloud services and APIs. To run code or samples from a local development environment, you can authenticate to Compute Engine by selecting one of the following options:

  To use the Python samples on this page in a local development environment, install and initialize the gcloud CLI, and then set up Application Default Credentials with your user credentials.

  1. Install the Google Cloud CLI.

  2. If you're using an external identity provider (IdP), you must first sign in to the gcloud CLI with your federated identity.

  3. If you're using a local shell, then create local authentication credentials for your user account:

     gcloud auth application-default login

     You don't need to do this if you're using Cloud Shell.

     If an authentication error is returned, and you are using an external identity provider (IdP), confirm that you have signed in to the gcloud CLI with your federated identity.

  For more information, see Set up authentication for a local development environment.

Get live migration notices

You can learn when live migration is about to happen for your instance by querying the maintenance-event metadata key periodically.

The maintenance-event metadata key is populated for maintenance events only if you have set your VM's scheduling option to migrate or if your VM has a GPU attached.

The value of this metadata key changes 60 seconds before a maintenance event starts, giving your application code a way to trigger any tasks you want to perform prior to a maintenance event, such as backing up data or updating logs.

Compute Engine gives the 60-second warning only if:

• You have set the VM's availability options to live migrate during a maintenance event.

• You have queried the maintenance-event metadata key at least once since the last maintenance event.

  • If you have never queried the maintenance-event metadata key or have not queried the metadata key since the last migration, Compute Engine assumes that the VM doesn't require advance warning of maintenance events. The maintenance event initiates immediately and skips the 60-second warning.

  • If you don't want to skip the 60-second warning, make sure your client code queries the maintenance-event metadata key at least once between migration events. You must query the maintenance-event metadata key directly for Compute Engine to determine that you are watching this metadata key. Querying a higher level metadata doesn't trigger the advance notice.

For VMs with attached GPUs, the value changes 60 minutes before the VMs are stopped to give you time to shutdown and restart again on another host. VMs with attached GPUs are not live migrated and are instead stopped and optionally restarted. To learn more, see Handling GPU host maintenance events.

Query the maintenance event metadata key

user@myinst:~$ curl http://metadata.google.internal/computeMetadata/v1/instance/maintenance-event -H "Metadata-Flavor: Google"

NONE

user@myinst:~$ curl http://metadata.google.internal/computeMetadata/v1/instance/maintenance-event?wait_for_change=true -H "Metadata-Flavor: Google"

PS C:\> 
$value = (Invoke-RestMethod `
         -Headers @{'Metadata-Flavor' = 'Google'} `
         -Uri "http://metadata.google.internal/computeMetadata/v1/instance/maintenance-event")
$value

NONE

PS C:\> 
$value = (Invoke-RestMethod `
         -Headers @{'Metadata-Flavor' = 'Google'} `
         -Uri "http://metadata.google.internal/computeMetadata/v1/instance/maintenance-event?wait_for_change=true")
$value

import time
from typing import Callable, NoReturn, Optional

import requests


METADATA_URL = "http://metadata.google.internal/computeMetadata/v1/"
METADATA_HEADERS = {"Metadata-Flavor": "Google"}


def wait_for_maintenance(callback: Callable[[Optional[str]], None]) -> NoReturn:
    """Start an infinite loop waiting for maintenance signal.

    Args:
        callback: Function to be called when a maintenance is scheduled.

    Returns:
        Never returns, unless there's an error.
    """
    url = METADATA_URL + "instance/maintenance-event"
    last_maintenance_event = None
    last_etag = "0"

    while True:
        r = requests.get(
            url,
            params={"last_etag": last_etag, "wait_for_change": True},
            headers=METADATA_HEADERS,
        )

        # During maintenance the service can return a 503, so these should
        # be retried.
        if r.status_code == 503:
            time.sleep(1)
            continue
        r.raise_for_status()

        last_etag = r.headers["etag"]

        if r.text == "NONE":
            maintenance_event = None
        else:
            maintenance_event = r.text

        if maintenance_event != last_maintenance_event:
            last_maintenance_event = maintenance_event
            callback(maintenance_event)


def maintenance_callback(event: Optional[str]) -> None:
    """Example callback function to handle the maintenance event.

    Args:
        event: details about scheduled maintenance.
    """
    if event:
        print(f"Undergoing host maintenance: {event}")
    else:
        print("Finished host maintenance")


def main():
    wait_for_maintenance(maintenance_callback)


if __name__ == "__main__":
    main()

Review the outputs

The initial and default value of the maintenance-event metadata key is NONE.

• For VMs with attached GPUs, bare metal instances, or other instances that don't support live migration, maintenance event the value changes from NONE to TERMINATE_ON_HOST_MAINTENANCE. This value is updated 60 minutes before the stopping event starts.

• For non-GPU VMs with a scheduling option of migrate, the maintenance-event value changes as follows:

  1. At the start of the migration event, the value changes from NONE to MIGRATE_ON_HOST_MAINTENANCE. This value is updated 60 seconds before the stopping event starts.
  2. Throughout the duration of the event and while your VM instance is being live migrated, the value remains as MIGRATE_ON_HOST_MAINTENANCE.
  3. After the maintenance event ends, the value returns to NONE.

• For sole-tenant VMs, during a host maintenance event, the maintenance-event metadata key value doesn't change and remains NONE from the start to the end of the event.

For machine series that support advanced maintenance capabilities, prior to a maintenance event you can query the metadata key upcoming-maintenance. If there is a notification available for your instance you should see values similar to the following:

{
   "maintenanceType":"SCHEDULED"
   "canReschedule": "true"
   "latestWindowStartTime": "2025-08-28T21:56:21Z"
   "maintenanceStatus": "PENDING"
   "windowEndTime": "2025-08-29T01:56:20Z"
   "windowStartTime": "2025-08-28T21:56:26Z"
}

To determine how long before a maintenance event the upcoming-maintenance metadata key is populated, see the "Maintenance experience" documentation for the machine series. For example, for Z3 machine types, see Maintenance experience for Z3 instances.

What's next

• Learn about setting instance availability policies.
• Learn how to simulate a host maintenance event.
• Learn more about live migration.
• Learn more about VM metadata.