Maintenance in ULL Solution private zones

This page provides an overview of the zone maintenance process for private zones used by Google Cloud Ultra Low Latency (ULL) Solution.

Overview of the dual-zone design for ULL Solution

ULL Solution uses a dual-zone design to help ensure that regular maintenance and testing can be performed without interrupting market trading. To support this design, the private zones used for ULL Solution have unique availability and maintenance properties compared to public zones in Google Cloud. For details, see the following:

  • Two private zones in a given region: A given region used by ULL Solution has two private zones. For example, the us-south1 region has the private zones us-south1-d and us-south1-e.
  • Only one zone supports production workloads at a given time: See the following:
    • The production zone is the active environment for live trading. To help maintain a stable environment in this zone, Google doesn't perform maintenance or updates.
    • The maintenance zone is the inactive environment in which Google performs updates and repairs, and exchange operators and participants can also perform updates and testing. The maintenance process includes unique windows that determine when Google performs updates and repairs, as well as when customers should perform recommended actions.
  • Weekly zone transition: The role of each zone switches on a weekly schedule that you can view by using gcloud or the API. Once per week, the existing production zone switches to the maintenance zone, and the maintenance zone switches to the production zone.

Requirements for exchange operators and exchange participants

Exchange operators and exchange participants must ensure that they run production workloads in the production zone, and perform updates and testing in the maintenance zone according to the recommended actions for each maintenance window.

For more information, see the following sections:

Zone maintenance windows

For the zone that is designated as the maintenance zone for a given week, the following sequential maintenance windows occur. For the specific start and end times of each window, see View zone maintenance status. For more details about each window, see the following Maintenance window details section.

Day Applicable maintenance windows Recommended actions for exchange operators and participants
Days 1 and 2
  • Disruptive upgrade window
 Avoid using the infrastructure as operations might fail.
Days 3, 4, 5
  • Customer maintenance window
 Provision instances, update software applications, and update infrastructure configurations. Perform functional testing.
Days 6 and 7
  • Stable window
 Conduct performance validation and stress testing.
End of day 7
  • Zone transition window
 Migrate production workloads.

Maintenance window details

The following table describes each maintenance window.

Maintenance window Description
Disruptive upgrade window

This window lasts for the first 48 hours.

Google performs updates that are likely to cause disruptions to instances and services. Using the infrastructure in the zone isn't recommended. While APIs might be available, operations are unstable.
Customer maintenance window

This window begins after the completion of the disruptive upgrade window and lasts for 72 hours.

Exchange operators and exchange participants can provision instances, maintain and update the software running on instances, update infrastructure configurations, and perform functional testing.
Stable window

This window begins after the completion of the customer maintenance window and lasts for about 46 hours.

During this window, the zone is stable and exchange operators and exchange participants can conduct performance validation and stress testing to prepare for active trading in the zone.
Transition window

This window begins after the completion of the stable window and lasts for about 2 hours.

The state of each zone is changing. The existing production zone is switching to the maintenance zone. The existing maintenance zone is switching to the production zone. During this window, Google performs preliminary, non-disruptive tasks.

Maintenance experience for U4 instances

The maintenance experience for U4 instances depends on the machine type:

  • ULL Compute Engine instances (U4P and U4C): ULL instances have a unique maintenance experience compared to other instance types in Google Cloud. These instances are maintained according to the maintenance schedule for ULL Solution private zones. The duration of host maintenance aligns with the disruptive upgrade window of the zone.
  • Non-ULL Compute Engine instances (U4S): Non-ULL instances have a maintenance experience that is generally consistent with other instance types in Google Cloud as described in Transparent maintenance. However, live migration of non-ULL instances due to upgrades isn't supported in the production zone.

For general information about maintenance of Compute Engine instances, see About host events.

The following table describes the host maintenance properties for U4 machine types.

Machine type Typical scheduled maintenance event frequency Maintenance behavior Advanced notification On-demand maintenance
U4P and U4C 14 days Terminate 14 days No
U4S 28 days Live migrate 7 days Yes

View zone maintenance status

You can view the current and upcoming maintenance details for a zone, including specific start and end times of each maintenance window, by using either of the following options. This feature is available only in the alpha API. If you haven't already, enable your project to use the alpha API as described in Use the Compute Engine alpha API.

The information about maintenance is presented in the response in a section similar to the following example:

"upcomingMaintenances": [
      {
        "type": "PRIVATE_ZONE_MAINTENANCE",
        "subType": "DISRUPTIVE_UPGRADE",
        "targetResource": "projects/my-project/zones/us-south1-d",
        "windowStartTime": "2025-08-26T15:00:00Z",
        "windowEndTime": "2025-08-27T15:00:00Z"
      }
      // Additional maintenance windows ...
    ]

While Google Cloud also provides an instance-level maintenance status as described in Monitor and plan for a host maintenance event, only the zone-level output provides the full maintenance schedule and window details for ULL Solution private zones as described in the following Field descriptions section.

Field descriptions

The following sections describe the unique fields available for ULL Solution private zones when describing a zone. The following fields aren't available for public zones in Google Cloud.

resourceStatus.upcomingMaintenances[]

An array of objects, where each object represents a scheduled maintenance window. Includes all ongoing and future maintenance windows scheduled within the next 7 days.

Field Type Description
type enum The type of maintenance. See type enum.
subType enum The subtype of maintenance. See subType enum.
targetResource string The full resource name of the zone undergoing maintenance (such as projects/my-project/zones/us-south1-d).
windowStartTime string Start time of the maintenance window in RFC 3339 UTC "Zulu" format (such as 2025-08-26T15:00:00Z).
windowEndTime string End time of the maintenance window in RFC 3339 UTC "Zulu" format (such as 2025-08-27T15:00:00Z).

type

Value Description
MAINTENANCE_TYPE_UNSPECIFIED Default value.
PRIVATE_ZONE_MAINTENANCE Maintenance that applies to a ULL Solution private zone.

subtype

Value Description
MAINTENANCE_SUBTYPE_UNSPECIFIED Default value.
DISRUPTIVE_UPGRADE Corresponds to the disruptive upgrade window described in Zone maintenance window details.
CUSTOMER_MAINTENANCE Corresponds to the customer maintenance window described in Zone maintenance window details.
STABLE Corresponds to the stable window described in Zone maintenance window details.
TRANSITION Corresponds to the transition window described in Zone maintenance window details.

warnings[]

An array of warning objects providing additional information.

Field Type Description
code enum A warning code. See warning.code enum.
message string A description of the warning.
data array Metadata about the warning in key/value pairs (such as [{"key": "scope", "value": "zones/us-east1-d"}]).

warning.code

Value Description
WARNING_CODE_UNSPECIFIED Default value.
UPCOMING_MAINTENANCES_UNAVAILABLE Upcoming maintenance window information can't be retrieved. Try again later.

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