System clone

  • Release version: Xanadu
  • Updated August 1, 2024
  • 3 minutes to read
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    Summary of System Clone

    The System Clone application enables ServiceNow customers to copy an entire database from one instance to another, typically from a production instance to a pre-production instance for testing purposes. Cloning uses data from the most recent nightly backup, ensuring data freshness up to 36 hours old. A new Clone Admin Console offers enhanced visibility and administration of cloning operations.

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    Clone Process

    When a clone request is initiated, the platform:

    • Generates a file preserving operational data on the target instance.
    • Copies the database schema and creates tables on the target instance based on the source.
    • Transfers data from the latest nightly backup of the source instance, excluding certain large tables like audit, log, and email tables by default.
    • Temporarily disables UI traffic and email functions on the target instance, displaying a "Clone in progress..." message to users.
    • Restores preserved operational data and runs post-clone cleanup scripts.
    • Queues an event to regenerate text indexes and then re-enables UI traffic.

    The target instance may be intermittently unavailable during cloning. Customers have up to 24 hours after completion to request a rollback to the pre-clone state via Customer Service and Support.

    Important Restrictions

    • Cloning is disallowed if the source instance has a clone depth level of 5 or higher.
    • Cloning from a source instance with the DART (Data Access for Responsible Training) purpose is prohibited.

    Version Compatibility and Upgrades

    The System Clone application supports cloning to a target instance running a different version. A central web service ensures the target instance is upgraded or downgraded to match the source version automatically, starting up to eight hours before the scheduled clone time. This version adjustment occurs during a brief downtime window.

    Backup and Legacy Engine

    The clone operation uses the latest nightly backup (max 36 hours old). If cloning from backup fails, the system falls back to a legacy clone engine with limitations, such as inability to preserve extended tables and complex relationships. In such cases, restoring the target instance from backup and rescheduling the clone is recommended.

    Cloning Over Production Instances

    If the system property glide.db.clone.allowclonetarget is set to TRUE, instances can be cloned regardless of their production status. However, modifying the source instance data during cloning can cause data mismatches or duplicate records.

    Deprecated Options

    The "Preserve users and related tables" option was removed in the Utah release and no longer affects cloning outcomes, even if it appears due to legacy customizations.

    Use the System Clone application to copy everything in a database from one instance to another.

    Cloning is typically used to copy a production instance to a pre-production instance to test changes. Cloning data comes from the most recent nightly backup.

    Note:
    A new, unified admin experience based on the existing clone engine is now available in the Clone Admin Console. The Clone Admin Console provides enhanced visibility for cloning data between instances, one of our most-used automations, as well as a number of other enhancements.
    Figure 1. Clone process

    Clone process overview
    In response to a clone request, the ServiceNow platform performs the following tasks:
    1. Generates a file to preserve operational data on the target server.
      Note:
      This file contains the data preserved by data preservers.
    2. Copies the database schema from the source instance to the target instance.
    3. Creates tables in the target instance database using the source instance table definitions.
    4. Copies data from the most recent nightly backup of the source instance to the target instance database.
      Note:
      Certain exclusions are automatic, large tables are normally excluded. These include audit, log, and email tables. MetricBase tables aren’t excluded by default.
    5. Briefly disables UI traffic and requests to the target instance server.
    6. Displays the message Clone in progress... to any user accessing the target instance.
    7. Restores operational data preserved from the target instance.
    8. Runs any post-clone cleanup scripts on the target instance.
    9. Briefly suspends all email functions on the target instance.
    10. Queues an event to regenerate text indexes.
    11. Enables UI traffic and requests to the target instance server.

    During a clone, the target instance may be intermittently unavailable. After clone completion, you have up to 24 hours to contact Customer Service and Support and request a rollback of the target instance to its pre-clone state. You’re notified when the rollback is complete.

    Note:
    If the source instance has a clone depth level of >=5 then the clone isn’t allowed.

    If the source instance purpose is DART (Data Access for Responsible Training) then the clone isn’t allowed and an error message will be displayed.

    Clone to an instance on a different version

    The System Clone application can target an instance running a different instance version from the source.

    A central web service controls the clone processing and automatically modifies the target instance version to match the source instance version. This matching process starts up to eight hours before the time specified in the Date and time field on the System Clone form. This web service also confirms that there’s enough disk space on the target instance for the clone to proceed.

    When cloning from a backup, the target instance doesn’t need additional time to upgrade or downgrade. The ServiceNow platform performs any version changes during a brief window where the target instance is unavailable, after it copies data from the source instance backup.

    Clone from a backup

    The clone uses data from the most recent, nightly backup of the source instance when cloning. Backups that are used for cloning are a maximum of 36 hours old. System Clone begins the initial preparation, including selecting the latest backup to use, only at the date and time processing is scheduled to start.

    If cloning from a source backup fails, the system uses the legacy clone engine instead. The legacy clone engine can’t preserve data from extended tables, relationships, hierarchies between tables, and dot-walked queries. You may want to restore the target instance from a backup and then reschedule the clone in such cases.

    After cloning from a backup, the target instance is unavailable for several minutes before the clone is marked as complete in the source instance. If the source and target instances are on different versions of the ServiceNow AI Platform, the target instance is modified to match the source instance version during this time.

    When starting a clone from a backup, the date and time the backup was taken, as well as periodic progress messages, appear in the Clone Log related list.

    Figure 2. System clone backup log
    Clone log backup record

    Clone over production instances

    As long as the system property glide.db.clone.allow_clone_target is TRUE, an instance can serve as a clone. Modifying data on the source instance during a clone can cause a data mismatch between records or duplicate record entries.

    Deprecated Clone Options

    The clone option check box Preserve users and related tables has been removed from Clone Options in the Utah release. In some cases, past customizations to the clone request page or related to clone, may cause this field to remain on your form.
    Important:
    Checking this deprecated field won’t have any effect on the user, role, or related tables during your clone.
    .